Review of Literature on Effects of Slurry

Use on Crop production

FINAL REPORT

Submitted by:
Jit B. Gurung, Ph.D.
Freelance Consultant
Post Box #2314, Kathmandu, Nepal
Telephone: 00977-1-520597
Fax/Tel.: 00977-1-535963

To:

The Biogas Support Program

Post Box 1966 Kathmandu, Nepal

June 1997

1
 TABLE OF CONTENTS
Page
Table of contents I-IV
Abbreviations V
Preface VI
Summary, conclusions and recommendations Vll-X
Chapter 1: Objectives, rationales and methodology 1 -4
1.1. Introduction 1
1.2. Rationales of the study I -3
1.3. Objectives 3
1.3.1. Overall objective 3
1.3.2. Specific objectives 3
1.4. Scope 3
1.5. Methodology 3
1.5.1. Interview 3
1.5.2. Literature search 3-4
Chapter 2: Nutrient constitution of bioslurry 5-18
2.1. Organic matter and plant nutrients 5
2.2. Nutrient supply 5-6
2.3. Improvements in the soil chemical,
physical, and biological properties 6
2.4. The nitrogen cycle vis-a-vis organic
matter 6
2.5. Nutrient composition of biogas
slurry in different forms 7-8
2.5.1. Overview of past research in
anaerobic digestion 7
2.5.2. Early research on the nutrient
value of slurry 7-8
2.5.3. Contemporary research on
nutrient value of slurry 8-1 5
2.5.4. Nitrification studies and the issues of
nitrogen conservation in digested slurry 15-17
2.5.5. Other nutrients 17
2.5.6. Bioslurry and the physical, biological
qualities of soil 18
Chapter 3: Effects of biogas slurry on crop production 19-51
3.1. Background to the study of manurial value of
biogas slurry 19
3.2. Contemporary research 19-51
3.2.1. Slurry research in Nepal 21 -24
3.2.2. Slurry research in other countries 24-43
3.2.2.1. Slurry utilization in seed treatment insect/pest
control and foliar
dressing 44-51
Chapter 4: Sanitation and public health aspects of slurry utilization in
crop production 52-67
4.1. Preliminaries 52
4.2. Excreta born organisms and diseases 52-54
4.3. Research in pathogen/parasite elimination
and survivability 54-65
4.4. Sanitary regulation 65
4.5. Biogas slurry utilization and health and sanitary
improvements 65

I
 4.6. Biogas slurry utilization and health and
sanitation in Nepal 66-67
Chapter 5: Slurry treatment 68-77
5.1. Biodigested fresh liquid slurry 68
5.2. Treatment of slurry 69-76
5.2.1. Liquid biogas slurry storage 69
• Application of liquid slurry 69-70
5.2.2. Dehydration 70
5.2.3. Filtration 70-71
5.3.2. Centrifugation 71
5.2.2. Composting of biogas slurry 72-76
5.2.5.1. Composting methods 72-76
5.2.5.1. a. Open window method 73-76
5.2.5.2. b. General composting 74
5.2.5.3. c. Pit composting 74-76
5.2.5.2. Pathogen/parasite reduction by composting 76-77
Bibliography 78-87
General references 88-93
Prologue 94-95
List of tables:
Table 1 : Effects of slurry on agricultural production 2
Table 2 : Advantage of slurry over dung 2
Table 3 : Total solid content (dry matter) of fermentation
materials commonly found in rural areas (approximation) 9
Table 4 : Carbon: nitrogen ratio of feedstock commonly
adopted (approximation 9
Table 5 : NPK values of fresh cow dung slurry 10
Table 6 : Composition of spent slurry from nightsoil biogas plant 10
Table 7 : NPK content of sun -dried bioslurry 10
Table 8 NPK content of bioslurry and FYM 10
Table 9 : Quality and composition of human faeces and urine 11
Table 10 : Characteristics of nightsoil 11
Table 11 : Manurial value of slurry and other characteristics
of human excreta fed to biogas digesters 11
Table 12 : Average composition of nightsoil and urine 11
Table 13 : Composition of spent slurry from nightsoil
biogas plant 12
Table 14 : Effect of digester manure on physical and
chemical properties of Soil 12
Table 15 : Comparison of loss of nitrogen between
digester manure and farmyard manure 12
Table 16 : Approximate range of nutrient contents of
digester manure 12
Table 1 7 : Average constitution of fresh dung, dung slurry,
digested slurry 12
Table 18a: Constitutions of different forms of organic manure 13
Table 18b : Average constitutions of fresh chicken dropping, and fresh
cattle buffalo, and pig dung from samples collected from
different parts of Nepal 14
Table 18c : Average constitutions of fresh slurry from biogas
plants with and without toilet attachment 14
Table 18d: Nitrification of digested slurry 15
Table 19a: Nitrification of digested slurry 15
Table 19b: Mean yield/pot of grain, straw of wheat and marua
(Eleusine coracona) and Total Dry Matter of sannhemp 20
Table 20 : Plot fertilizer experiment, Maya Farms, Philippines 20
II
Table 21 : Mean yield of rice (grain) and berseem (dry fodder) 21
Table 22 : Effect of biogas slurry (dry and fresh on wheat yield) 21
Table 23 : Comparison of the effects of biogas
slurry and other manures on wheat yield 22
Table 24 : Effects of biogas slurry on paddy, tomato,
cauliflower, French bean, wheat, and maize 22
Table 25 : Effect of biogas slurry on wheat yield under
irrigated and rainfed conditions 23
Table 26 : Effect of azotobactor inoculation of biogas
slurry and other compost manures on wheat yield (kg/ha) 23-24
Table 27 : Comparison of the effect of effluent and FYM
on the yield of rice, maize, wheat, and cotton 25
Table 28 : Comparative yields of cucumber for varying
quantities of effluent vis-a- vis chemical fertilizer 25
Table 29 : Comparative effects of different doses of slurry
and slurry-chemical fertilizer combinations on tomato production 25
Table 30 : Effect of biogas slurry with and without mineral fertilizer
on mungbean yield 26
Table 31 : Effect of biogas slurry with and without mineral
fertilizer on sunflower yield 26
Table 32 : Average yield of vegetables with mineral fertilizer and
effluent application 27
Table 33 : Changes in soil NPK levels after slurry application 27
Table 34 : Effects of various fertilizer combinations on the
yields of cabbage, mustard, and potato 28
Table 35 : Effect of slurry on the yield of different crops in India
(Khariff, 1988) 28
Table 36 : Effect of biogas slurry on crop yield in the Indian States
(Rabi, 1988-89) 29
Table 37 : Effect of different types of manures and
fertillisers on the growth of tomatoes 29
Table 38 : Effect of different types of manures and fertillisers
on growth of chillies 30
Table 39 : Summary of results of slurry demonstrations
conducted by concerned state departments/agencies
in India (1984-85 to 1990-91) 30-31
Table 40 : Summary of results of demonstrations on the effect
of biogas slurry on crop production (GSFC, India, 1989-90) 31
Table 41 : Summary of the evaluation of manurial value of biodigested slurry
for various cereals and other crops in different agro-climatic zones
in India 32-33
Table 42 : Effect of biogas slurry on rice grain and straw yield in South India 34
Table 43 : Effect of biogas slurry in crop yield in China 35
Table 44 : Comparative effects of digester effluent and open
air pool manure on crop yield 36
Table 45 : Effect of digester sludge on crop yield in China 36
Table 46 : Effect of digester effluent + (NH4)HCO3
on the yield of rice and maize in China 36
Table 47 : Details of the study pertaining to comparative
effect of different fertilizers on pea, okra, soybean, and maize in
Himalchal Pradesh, India 37
Table 48 : Effect of biogas slurry on pod/cob size, plant height
and yield of pea, okra, soybean and maize 38
Table 49 : Comparative effects of chemical fertilizer
and biogas slurry + chemical fertilizer on various crops,
North Karnataka. India 39
III
Table 50 : Direct and residual effect of bio-digested slurry on
rice and blackgram 40
Table 51 : Effect of plain and enriched slurry on rice-blackgram cropping
system 40
Table 52 : Effect of biogas slurry and chemical fertilizer on
different vegetable crops 41
Table 53 : Effect of biogas manure on crop yield in Egypt 43
Table 54 : Yield of string bean treated with different organic
manures and chemical fertilizers 43
Table 55 : Effect of seed coating biogas slurry on rice yield 45
Table 56 : Seed coating In sorghum Tamil Nadu, India 45
Table 57 : Efficiency comparison of seed coating with digester
slurry and fresh water (rice) 46
Table 58 : Comparison of results of different seed soaking methods (wheat) 47
Table 59 : Excreta-borne organisms and diseases 53
Table 60 : Percent reduction of helminth ova in laboratory night soil digester 55
Table 61a : Survival time of pathogens In some excreta disposal system 56-57
Table 62b : Temperature, residence time and die-off rate of parasites and
pathogens 57
Table 62 : Comparison of pathogen survival in unheated
digestion and composting 57-58
Table 63 : Organisms isolated from farm manures and non-digested nightsoil 58-59
Table 64 : Settling time of some of the common pathogenic ova 62
Table 65 : Survival periods of schistosome ova 62
Table 66 : Fatality rates of hookworm ova 63
Table 67 : Fatality rates of ascaris ova (summer and autumn 63
Table 68 : Pathogen survivability under different temperatures 68
Table 69 : Relation between feedstock concentration and the
survival time of schistosome ova 64
Table 70 : Comparison of FYM and biogas slurry pit composting 74
Table 71 : Constraints faced by farmers in slurry compost making 75
Table 72 : Quality of compost against FYM 75
Table 73 : Farmers, perceptions on the quality of slurry compost 75
Table 74 : General composition of slurry compost based on
cattle dung based slurry 76
Table 75 : Effect of biogas phospo-humate on major crops 76
Table 76 : Pathogen elimination and survivability in unheated
anaerobic digestion and composting 77

IV
 Abbreviations

APROSC Agricultural Projects Services Centre

APRBRTC Asian-Pacific Regional Biogas Research-Training Center, Chendu, China
AFPRO Action for Food Production
ATC Agricultural Technology Center
AAU Assam Agricultural University
BSP Biogas Support Programme
CIE Central Institute of Agricultural Engineering (India)
C:N Carbon Nitrogen Ratio
C:P Carbon Phosphorous Ratio
CMS Consolidated Management Services
CD Critical Difference
DevPart Development Partners-Nepal (P) Ltd.
DOST Department of Science and Technology (India)
ENFO Environmental Sanitation Information Center (Bangkok, Thailand)
FYM Farmyard Manure
FORRAD Foundation for Rural Recovery and Development
g Gram
GSFCI Gujrat State Fertilizer Co-operative (India)
GGC Gobar Gas Company
HRT Hydraulic Retention Time
HPAU Himalchal Pradesh Agricultural University (India)
ha Hectare
ICIMOD International Center for Integrated Mountain Development
IARI Indian Agricultural Research Institute
IFFCO India Farmers' Fertilizer Co-operative
Irs Indian Rupees
kg Kilogram
LARC Lumle Agricultural Research Center
Ib Pound
MGT Mean Germination Time
MRL Mean Root Length
MSL Mean Shoot Length
MNES Ministry of Non-Conventional Energy Sources (India)
NPK Nitrogen, Phosphorous, Potassium
NARC National Agricultural Research Centre
O.M. Organic Matter
PARC Pakhribas Agricultural Center
PAU Punjab Agricultural University (India)
RAJAU Rajasthan Agricultural University (India)
SEP Slurry Extension Programme
SNV Netherlands Development Organization
SSP Single Superphosphate
SDS Sun-dried slurry
TERI Tata Energy Research Institute (New Delhi, India}
TS Total Solids
TNAU Tamil Nadu Agricultural University (India)
t Ton
UAS University of Agricultural Sciences (Karnataka, India)
W/W Weight by Weight
WECS Water and Energy Commission Secretariat

V
 PREFACE

This study is a review of literature pertaining to the use of slurry, a by-product {some prefer to call it 'primary
product' in view of its perceived importance as a high value fertilizer) of biogas plant, in crop production.
Virtually no research work is currently under way on this important aspect of biogas technology in Nepal. Few
preliminary works were initiated during the late 1970s after the incorporation of biogas promotion programme in
the Agriculture Year (1974-75). However these works stopped abruptly after few trials in Khumaltar. After a two
decade long hiatus, the interest on the issue has been aroused once again by SNV Nepal's Biogas Support
Programme. It was understood right in the beginning of this study that materials on this aspect are scanty in
Nepal. Nonetheless, some efforts were made to search materials in the major institutions and
documentation/information centres both in Kathmandu and in other areas of Nepal. No substantive review
materials were available. Since India is an important 'biogas country', and since both the biophysical and socio-
cultural environments, at least at the macro level, are similar to that of Nepal, a trip to Delhi was planned and it
was fruitful from the point of view of the task at hand.

While in Delhi Dr. K.N Khandelwal, adviser to the Ministry of Non-Conventional Energy Sources and head of its
Rural Energy division, gave me important advises about where to visit and whom to contact in Delhi; Mr Anil
Dhussa of the same ministry also extended his cooperation. The discussion with Mr. ]. B. Singh of FORRAD
(Foundation for Rural Recovery and Development) was very useful. Together these individuals can be
considered as the doyens of Indian slurry research activities. I am grateful to them all. The people at the Tata
Energy Research Institute library were very cooperative. 1 must thank them for this and their excellent library.
Special appreciation is also extended to Mr. Balbir Singh of the TERI library for responding to my queries and
for being ready to help me whenever I needed him during my work in that library. The cooperation extended by
all other individuals in Delhi is also gratefully acknowledged.

In Nepal, the guidance provided by Mr. Wim J. van Nes, Programme Manager of the SNV/ Biogas Support
Programme is gratefully acknowledged. The materials provided by him were immensely important for
understanding the state of biogas technology in Nepal. Mr. Bhimsen Gurung, the Slurry Extension Specialist
with the BSP, was always at hand to share whatever relevant material he could garner during the course of his
work. I must thank him for that.

In addition the cooperation extended by the following individuals is acknowledged:

Mrs. Renu Sherpa, BSP, ]hamsikhel, Lalitpur

Mr. L.K. Amatya, Lumle Agricultural Research Centre, Kaski, Pokhara.
Mr. K.B. Kadayat, Lumle Agricultural Research Center
Mr. Ananta Ghimire, Pakhribas Agricultural Research Center, Dhankuta.
Mr. Gam Bahadur Gurung, Pakhribas Agricultural Research Center, Dhankuta.
Mr. D.P Sherchan, Pakhribas Agricultural Research Center
Mr. Dawa Sherpa, PARC Documentation Center.
Ms. Indira Shrestha, PARC Documentation Center
Mr. Khadka Jung Gurung, Consultant

Jit B. Gurung, Ph. D. May, 1997

VI
 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Summary & Conclusions

1. A review of the brief history of anaerobic digestion showed that the energy part (methane generation)
received more attention since the early decades of this century when research into biodigestion had
gradually begun to take shape. Fertilizer aspect received occasional attention a couple of decades latter.
Emphasis on the. energy aspect still dominates in many parts of the world today (with the notable
exception of China). However, the environmentalism of the more recent years have somehow turned
to be conducive for the appreciation of slurry manure as well as biogas technology as a whole.

2. This review was centred mainly on the effects of bioslurry utilization in crop production. Major research
works, specially those carried out in India and Nepal, on the effects of different forms of slurry on
crop yields were reviewed. Brief attentions to the works carried out in the area of nutrient
research (especially, nitrogen), the health and sanitation aspects of bioslurry utilization in agriculture
and slurry were also given.

3. There seems to have built a general consensus on the ability of biogas slurry to improve the physical and
biological quality of soil besides providing both macro and micro-nutrients to crops. These
improvements in physical and biological qualities include: improvement in soil structure, improvement
in water holding capacity, cation exchange capacity, lesser soil erosion and provision of nutrients to soil
micro-flora including nitrogen fixing and phosphorous solublizing organisms. In addition bioslurry is
free of weed seeds. Anaerobic digestion kills more seeds than any manure processing system (It is
not the methane that kilts the seeds; it just inhibits germination. Most importantly, it is the free
ammonia that kills the seeds). On the other hand, FYM, if left to itself, (open pool manure) looses
nutrients, most importantly, nitrogen, and thus possess relatively lower manurial value than biogas
slurry. Fresh dung also contains viable weed seeds that compete with the crops and requires farmers
to put extra labours for weeding. From the points of view of nutrient recycling, sustained agricultural
production, and forest and environmental preservation, the use of forest wood, agricultural and
animal wastes as fuel (which constituted 72%, 16% and 9% of the total energy consumption of
Nepal in 1992/93), is not a desirable practice. Biogas technology provides alternatives to both fuel
and fertilizer.

4. The review reveals that analysing the composition, and thus determining manurial values, of fresh
slurry, sun dried slurry, and slurry compost is an exceedingly complicated endeavor, effected, as it is,
by numerous varieties of circumstances ranging from sampling procedures to animal species to
feedstocks fed both to the animals and biogas plants. The literature reveals an almost idiosyncratic
constitutions of these different forms of biogas slurry. Furthermore, research reports often do not
clearly elaborate the research protocols and procedures about how different figures are arrived
at. Because of these, a comprehensive picture of the composition of different forms of biogas
slurry is lacking. Even with these limitations, following extension educational messages could be
give to the farmers:

• Storage, handling, treatment and application procedures are very important for nutrient
conservation and increased crop yield. In no way manures in all these forms should be
recklessly exposed to the vagaries of nature.
• Biogas digester does not ' use up' plant nutrients
• As there may not be congruence between the time of availability of fresh slurry and the time
of field application, liquid slurry should be properly stored or composted. If liquid application is
not practical, composting is the best alternative. Here comes the importance of having 2-3
compost pits near the biogas plant.
• No form of biogas slurry can be profitably left spread on the field. Fields should be
ploughed immediately, or if the manure is used as top-dresser, should be covered by soil
immediately, Nutrients.
• Biogas plants with toilet attachments can significantly improve health and sanitation of community
VII
 and community members.
• Use of fuel-wood, agricultural and animal wastes for fuel will gradually deplete soil nutrients and
thus contributing to the emergence of unsustainable agricultural systems. Although FYM can be
directly returned to the soil or composted to complete the nutrient cycle, its utilization in biogas
generation has two pronged advantages i.e. energy and better manure (if handled and treated
properly).

In addition, the review reveals a number of findings on the comparative effects of slurry and other
organic manures and chemical fertilizers on yields of a number of crops. These may be of potential
benefits to farmers if they are suitably translated to the local situations.

5. Some of the major findings1 pertaining to the comparative effects of slurry and other organic manures
and chemical fertilizers on crop yield are summarized below for their potential use by Slurry Extension
Officers. However these findings are presented to serve 'sensitizing' purposes only, for both the
manurial value of slurry and their potential applications for different crops are dictated by numerous
factors including animal and biogas plant feed stocks, treatment and handling procedures, agro-climates
and geophysical environments.

Effects on crop yields

• A combination of biogas slurry @ 12.5 t/ha and 100% NPK had pronounced effect on rice
yield.

• Seed coating with a combination of digested slurry at 50% (W/W) of seed + inorganic nutrient at
2% + biofertilizer at 2% enhanced growth and yield attributes of rice.

• Application of biogas slurry @ 10 t/ha to the first rice crop favourably influenced the following
blackgram crop. Slurry increased rhizobium nodules and increased the blackgram yield by around

78%.

• Gypsum enriched slurry when applied in combination with 75% recommended NPK gave
maximum grain yield in rice-blackgram cropping system. Estimations showed that 25 kg N/ha was
saved.

• Biogas slurry applications on wheat, sunflower, sunflower, hybrid cotton, and groundnut gave an
average yield increase of 24% over the control.

• Application of biogas slurry @ of 10 t/ha in potato, tomato, brinjal, groundnut, jowar, maize, and
okra gave better yields than FYM. (Reports, however, are usually not clear about the physical form
of the slurry used)

• Seed coating with 50% (W/W of seed), organic nutrient at 2% and biofertilizer at 2% also
increased the growth and yield of soybean, blackgram, greengram, and jowar.

• Yield increases due to bioslurry application, have also reported for many other crops including peas,
mustard, watermelon, cabbage, banana, chillies, bajra, turmeric, sugarcane, deccan hemp,
mulberry, tobacco, castor, and onion.

• A combination of liquid biogas slurry and chemical fertilizer enhanced carbon nitrogen
transformation with substantive effect on crop yield. The yields in many instances are reported to
be higher than that given by the combination of ordinary FYM and chemical fertilizer. In China
although the average yield increment reported is not as high as in India (somewhere around 10 to
18 percent), experiments in bioslurry-chemical fertilizer utilization showed yield increment by as

1
It should, however, be considered that these results are based predominantly on slurry research done in India and slurries used
were mostly derived from cattle and buffaloes. Some of the findings on slurries derived from human excreta are given in the
main text.

VIII
 high as. 37.8% in maize as compared to 16.8% and 9.4% respectively for effluent and chemical
fertilizer alone. A comparatively lower, nonetheless increased yield, has also been recorded for rice
with such combinations.

• Vegetable crops produced with bioslurry have better quality as compared to those produced with
chemical fertilizer. Studies have not pinpointed the differences between bioslurry and FYM in this
regard.

6. Nitrification research carried out so far indicate that properly handled bioslurry as a manure is superior
to ordinary farmyard manure. Mineralization rate of nitrogen is higher in biogas slurry than in ordinary,
undigested manure, which alone provides a sound empirical basis for slurry extension programmes. This
is the majority view and is technically right However, dissenting views begin to arrive in the picture
(elaborated in detail in the main text) when discussion of the preservation of nutrients from the digester
to the field takes place. This quote from Van Brakel is pertinent here: 'During the early 1950s, when
interest in anaerobic digestion in Germany was greatest, it was argued that the loss of cellulose and
nitrogen during conventional manure processing was about equal to the amount of these chemicals sold
in Germany in 1950. With nitrogen losses during conventional manure processing of 18% or higher,
anaerobic processing of manure would seem very attractive, because in principle, nitrogen losses during
this process can be zero. Moreover, it may be expected that manure processed anaerobically contains a
large amount of nitrogen that is readily assimilated by plants. Various laboratory experiments support
the contention that these advantages hold. However, there is a difference between what is possible in
principle and how things turn out in practice' (Van Brakel, 1980:104). Thus, the way slurry is
handled after it comes out of the digester for Van Brakel, is a matter of utmost importance. His
conclusion is that superior manurial value of slurry cannot be taken for granted just because it is
anaerobically digested; attention must be given to nutrient conservation from the moment it comes out
of the digester to the moment it is applied in the field. However critics of slurry promotion like Van
Brakel and Tam et al.(1983) are pessimistic about preventing nitrogen fosses from the small scale
operations in rural areas and see no advantages in slurry promotion. This is exactly where the role of
education, in the form of slurry extension, is important, for slurry extension agents can closely work
with the farmers to jointly identify the major causes of nutrient losses and advise and facilitate the
mitigation of these causes.

7. In the field condition, the effects of fresh slurry (cattle and buffalo) vis-a-vis- sun-dried slurry, was at
times, ambiguous. Toxicity, mainly due to hydrogen sulphide and excess ammonia accumulation, is
often presumed to be the reasons in many cases.

8. Significant number pathogens/parasitic species are eliminated by the anaerobic digestion process.
However, both temperature and HRT is an unsettled issue among the researches. It has been accepted
by all the researchers that the level of temperature is the determinant of not only the elimination rate of
pathogens, it is also an important determinant of which group of methanogenic bacteria will function in
the digester. Reports from various experiments have shown that pathogens are killed faster and the
slurry well digested in the thermophilic range of temperature(48-60°C). But the production of this
range1 of temperature requires external source of energy. Mesophilic methanogenic bacterial digestion
(3OJ4O°C) is considered ideal for household biogas plants, but again maintenance of a common
temperature range is important--a temperature fluctuation by a mere 2-3° C affects the methane forming
bacteria. The idea of fixing appropriate temperature for the elimination of different parasites and parasitic
ova has not reached consensus in the literature. The design aspect also enters into the debates and
controversies. Nonetheless, it is accepted that the remaining number of pathogens and parasites/parasitic
ova can be substantially reduced if bioslurry is used for composting.

9. On the whole, fresh slurry is better in terms of manurial value than ordinary farmyard manure, ordinary
compost and other forms of slurry (sun-dried, slurry compost). Field results are however highly
dictated by soil, moisture conditions, slurry storage modes, and application procedures. Nutrient
conservation during liquid storage, composting and drying is very important to utilize the true potential of
fresh slurry. Transportation of liquid slurry, however, is a major constraint in the South Asian context.

IX
10. Slurry derived from human excreta is far more superior in terms of manurial value, but wide scale
adoption of this technology has not taken place in Nepal and India. In comparison, China is doing far
better in this aspect. Sociocultural traditions rather than scientific facts seemed to be dominant in this
aspect. Slurry utilization in agriculture affected public health and sanitation in very positive and
substantive ways { the case of China). Some indications of these are also available from India and
Nepal. Utilization of human waste in biogas generation can be expected to significantly improve health,
and sanitation in the rural areas of Nepal. In India, it has been reported that 80% of the human'
diseases are due to the inability to manage human and animal waste properly. The annual loss in
medical expenses and lost labour is estimated be around IRs 4.5 billion. The Nepali situation cannot
differ much as far as pathogen contamination through unmanaged human and animal waste is
concerned.

11. Slurry research in Nepal has ceased to exist since the late seventies. Information on slurry utilization
suitable to Nepal's agro-ecology and climate is conspicuously lacking. Many research reports reviewed
were uninterpretable. This indicates the relatively lower level of scientific sophistication and statistical
rigorousness in slurry utilization research.

12. Finally, it seems that contemporary engagement with biogas technology with its two-pronged benefits-
fuel and fertilizer-- is a reflection of the emerging concepts of sustainable development, ecology and
environment. The ideas of ecological agriculture as reflected in the concepts of organic farming, natural
farming, permaculture, and sustainable agriculture can be considerably enhanced with the adoption of
biogas technology.

X
Recommendations
1. Available literature indicates that chemical fertilizers suppress soil microbial activities while biogas
slurry provides them energy. While it is difficult to find reports saying FYM be a suppressor of soil
microbial activity (organic manures as a whole is generally considered more soil microbe friendly
than chemical fertilizers), comparative studies of soil microbe friendliness of slurry and FYM is
lacking. Such a study will benefit the Slurry Extension Program in devising its extension messages.

2. Studies have generally revealed that fresh slurry, properly stored slurry and composted slurry
when combined with chemical fertilizer generally gives better crop yields than FYM + chemical
fertilizer. Fresh slurry or properly stored slurry alone has also given better yields than FYM alone. If
complete substitution of chemical fertilizer is not possible at high chemical fertilizer input areas at this
stage, use of bio-slurry, at least in combination with chemical fertilizers, should be encouraged. In the
mean time, as a comprehensive, comparative picture of composition of different forms of slurry
and FYM is still lacking in the varied situations of Nepal, samples of these organic manures should be
analysed to get the same and to backstop the Slurry Extension Programme with dependable technical
information.

3. No ready extension messages are available regarding the relative appropriateness of organic materials
for slurry composting. Scattered information on the composition of organic materials that are
available in and around farms in Nepal should be collected and reviewed for their potential
inclusion in slurry extension messages. Those plants and organic materials, the composition of which
is not available in the literature, should be analysed.

4. Biogas slurry utilization should be seen (because it is so) as an integrative mechanism between energy,
environment and agriculture. Even a partial substitution of chemical fertilizer (in the high chemical
fertilizer input areas) by bioslurry will improve soil health, reduce pest infestation, and increase crop
yield. In addition, the quality of some of the vegetables will be substantially better. These
recommendations are made on the basis of studies done abroad with the assumption that at least
no harm will be caused to the farmers due to the lack of data from Nepal

5. Experimental results vary substantially from place to place (soil, climate, form of bioslurry, feedstock
fed to the plants, crop species and varieties, irrigation etc.) thus trials and demonstrations should be
location specific.

6. Research in slurry utilization seems to have taken two modes. One mode is in line with the present
thinking with the Farmer Participatory Action Research (Gurung, 1997) which is based on a
epistemological premise that is different from the conventional, centralized institution based positivistic
and empiricist orientation that demand high level of statistical regour. Proponents of the latter tend to
believe that research should be for research's sake (excessive zeal for sophisticated designs). On
the other hand, the proponents of the former mode believe that such a practice of science has
lesser potential to help the farmers (Singh, 1977, personal communication). The proponents of
what might be called the scientistic mode question the scientific validity of the conclusions reached
by the former mode. Extreme position from either side is not going to be helpful. A middle of the
road approach i.e. Farmer participation with due regards for validity, is a desirable strategy for
slurry research programme in Nepal.

7. Research on slurry utilisation is usually a lesser priority area in many countries with Biogas Programmes.
European and North American Commercial and chemical farming naturally put lesser degree
of emphasis on slurry utilisation for crop production. During the mid-Eighties Demuynck
(1984:147) reported that only Denmark, Switzerland and Germany among the European countries
were studying the fertiliser value of digested slurry, in Nepal, institutional responsibility is not
entrusted to any existing research facilities. The works initiated during the late seventies stopped
abruptly. Current thinking on sustainable development in general, and sustainable agriculture in
particular demands substantive and aggressive steps towards ecological agriculture. Research
should take up from the currently existing knowledge to a systematic, farmer-based participatory

XI
 slurry utilisation action research, taking into consideration agro-ecological and climatic specificities
of Nepal.

8. Even the country's premier agricultural research institutions tike Pakhribas and Lumle have not yet done
any work on slurry utilisation. Given their competence and facilities (the lab in Pakribas for example)
they could be fruitfully integrated into the slurry participatory action research agenda.

9. Pathogens/parasitic ova survivability in digested slurry derived from human excreta is one issue, socio-
cultural traditions inhibiting the productive utilization of this resource is an altogether different issue
(China and India can be compared here). Research and extension efforts can be judged successful if
some of the cultural constraints (taboos) associated with human faeces are effectively deconstructed and
the nutrient rich product of the human biological system attained prestige as an important resource in
the resource poor agricultural countries like Nepal.

10. Anaerobic digestion can significantly reduce pathogens and parasitic ova both in animal dung and
human excreta; composting of slurry can kill the remaining pathogens/parasitic ova in the slurry.
Anaerobic digestion can play an important role in the improvement of sanitation and public health.
Vigorous educational campaigns are important here, and Slurry Extension Programme can play an
important role in this.

11. The Slurry Extension Programme of the Biogas Support Programme intends to investigate into the
possible involvement of the Department of Agriculture in slurry extension. This is an important idea the
materialization of which should be pursued as soon as possible because this department has the most
comprehensive country-wide extension network among the government agencies. The extension
activities of the Department of Livestock Development and Animal Health could also be fruitfully
coordinated with the Slurry Extension Programme. Such a mechanism would facilitate the use of
existing livestock and agricultural commodity groups (farmers' groups) for dissemination of messages
pertaining to slurry management and utilization in agriculture.

12. Nepal still has to initiate research activities in slurry utilization in agriculture. Nepal needs a series of
participatory trials on the effects of slurry application on crop yields in its various agro-ecological and
climatic zones. In the context of the BSP, it may carry out these activities in collaboration with
competent individuals from non-governmental organizations, or alternatively, the Slurry Extension
Programme of the BSP could train the SEOs for simple participatory trials and demonstrations. Such
participatory trials, in the long, will be able to generate sufficient data to be incorporated in the slurry
extension work. The current forms (Awareness Creation, Baseline Information, Farmers Visit, Result
Evaluation,) used by BSP's SEP will mostly catch perceptions, opinions, and practices (as recalled) ; and
over the years, the information captured by these forms will definitely provide important images of
different aspects of slurry utilization. The information generated by farmer participatory trials and the
information captured by the forms currently used by the SEP, when synthesized, can be expected to
greatly enhance the SEP.

XII
 CHAPTER 1

OBJECTIVES, RATIONALES AND METHODOLOGY

1.1. Introduction

In Nepal, the traditional sources of energy include fuel-wood, agricultural residues and animal wastes. It
has been estimated that these sources of energy met 91 percent of Nepal's total energy consumption for
the year 1993 (WECS, 1994). Fuel wood accounted for around 68 % of the total energy consumption;
the rest, around one fourth of the total consumption, was supplied by agricultural and animal wastes. In
the situation of the dwindling forest area, which cannot meet the fuel-wood demand, and in the
situation of the limited affordability of other sources of energy, felling of more trees arid burning of
agricultural and animal wastes become the immediate ways to solve energy problems. The consequences
for the environment and soil nutrient cycling is obvious. It has now been generally accepted that in many
parts of the country, the fertility of soil is declining due to continuous cultivation without replenishing
soil nutrient removal by crops with quality fertilizers in required quantity. Nepal does not produce
chemical fertilizers and most farmers cannot afford to buy the imported fertilizer. Even for those who can
afford to buy fertilizer, the undependability of availability has usually been a problem. Under these
circumstances, putting emphasis on locally available low cost organic manure becomes an important option.
In this context, the accelerated pace of biogas adoption in Nepal in the past few years offers possibilities
for both fuel and locally produced organic fertilizer. In addition to energy generation, other major
aspects of bio-gas technology is the bi-product known as bioslurry. Ideally, the efficient use of
bioslurry as fertilizer should be an important dimension of the diffusion and adoption of this technology.
With increasing number of bio-gas plants, slurry utilization for raising agricultural production and
productivity has also begun to be a concern, since not using or misusing bioslurry is to deprive the
organically poor soil from this potentially fertility enhancing resource. In addition, replacement of fuels
from agricultural wastes, animal wastes and wood by fuel from biogas plants helps protect forests and
supply soils with nutrients.

1.2. Rationales of the study

Many consider digested biogas slurry as important as biogas itself, it contains important plant nutrients and
its use is consistent with the ideas inherent in sustainable agriculture and sustainable development, the ideas
to which contemporary development thinkers and practitioners are putting much emphasis. Both the
energy and the fertilizer provided by biogas plants form integral parts of an ecological cycle, and
ecology is what sustainable development is importantly concerned with.

Nepal imports more than Rs 250 million of chemical fertilizer every year. It has been estimated that
proper use of slurry produced by the potential number of biogas plants would save 54 percent in the
purchase of N, 85 percent in P2O5 and a whopping 1,761 percent in K2O from the projected demand of
these nutrients for the year 1996/97 (CMS, 1996:4-3). Despite the usual scientific claims that
anaerobically digested slurry enhances soil fertility, and despite the estimations of potential replacements of
mineral fertilizer, there does not exist too much reliable information on the influence of slurry on crop
production.

A survey on GGC bio-gas plants (1990-91) (Gajurel et al., 1994:11-12) reported that 34 percent of
the users were ambivalent about the 'fertilising value' of the bioslurry. East Consult (1994:22) in one of its
studies reported that 52% of the respondents felt that "crop yields may decrease as all the nutrients
in the dung were burnt off"; only 15 percent of the survey respondents felt that crop yield increased after
the use of bioslurry. Another study conducted by Castro et al. (1994:21-22) reported that farmers in

1
general insisted that the increase in crop yields because of the use of slurry has not been proved'.
The farmers also reportedly felt that fertility effects of the slurry would not last as long as that
of the raw dung. Another bio-gas survey for the year 1994-95 (East Consult, 1996 :24)
reported that only 20 percent of bio-gas users among its respondents were using bioslurry.
The shorter time periods between the construction of biogas plants and the conduction of some
of these surveys should, however, be noted. DevPart (1996:36) reported that 93 percent of its
respondents were reportedly using biogas slurry. Also DevPart's inquiry into the effects of
slurry in agricultural production among biogas users (ibid.) reported that 19% of the user
respondents experienced some increase in agricultural production. Some respondents (24%)
even reportedly witnessed a decrease in production after the use of bioslurry. The replacement
of inorganic fertilizer among these respondents was also reportedly not very encouraging as
only 21% reported that they have lowered the quantity of inorganic fertilizer use after they
stated using bioslurry. Table 1. below presents responses on the effect of bioslurry on
agricultural production among respondents with and without toilet connection and among those
without toilets.

Table 1: Perceptions on effects of slurry on agricultural production

Effect Toilet not connected Toilet connected Toilet not Row total
constructed *

Increased significantly 1 5 1 7
Increased somewhat 7 8 4 19
Remained same 8 9 2 19
Decreased 8 12 4 24
Cannot say 11 18 2 31
Column total 35 52 13 100
Source: DevPart- Nepal, 1996:36 * Biogas adopters who do not have toilets
DevPart (ibid.) also made an attempt to assess the users' perception on the effectiveness of slurry
over the farm-yard manure. Table 2 below presents data on such perceptions among
respondents with and without toilet connection and among those respondents who did not
have toilets constructed

Table 2: Advantage of slurry over dung

General perception Toilet not Toilet connected Toilet not Row total
connected constructed*
Better than dun? 1I 14 4 29
Same as dung 6 10 3 19
Less fertile than dung 16 21 4 41
Cannot say 2 7 2 II
Column total 35 52 13 100
Source: DevPart- Nepal, 1996: 36 * Biogas plant adopters who do not have toilets

Table 2 above shows that 41 % of the respondents think that bioslurry is less fertile than dung. In
comparison only 29% thinks that bioslurry is better than dung.

The DevPart study also reports that the general perception of the biogas adopters is not effected
by the toilet connection. In addition DevPart (1996:36) reports: 'In absence of reliable data on
the actual increase or decrease in agricultural production because of the installation of biogas
plants', it is difficult to quantify the benefits in monetary form. There is no reason to believe
that production has increased significantly because of the installation of biogas plants. The major
reason for this could be improper handling of the slurry and the lack of composting practice'.
Furthermore, a big majority of the user respondents (86%) also reported that the quantity of

2
available manure decreased significantly, affecting manure-supply on the fields.(ibid.).

These reports indicate that bio-gas adopters in Nepal have neglected the proper use of bioslurry as
fertiliser. Thus it seems that in the past little ' attention has been focused by the promoters as well as
extension workers to promote scientific data in this subject' (CMS, 1996:4-5).

The rationales of this study are thus dear. There is a need to look into research works pertaining to the
manurial values of digested slurry and their subsequent effects on crop production. This is important for
biogas extension programmes because bio-gas owners ' seem to be misled about its effect on agricultural
productivity' (Adhikary, 1996: 15). The SNV Biogas Support Programme (BSP), a premier biogas
promotion programme in Nepal, recognizes this aspect of biogas promotion, in fact ' to increase
agricultural production by promoting an optimal utilization of digested dung as organic fertilizer'
(Cited in Britt, 1994:6) is one of the long term objectives of the BSP. After a review of studies conducted
for the BSP Britt (ibid) has identified the following specific research areas to determine: 1) whether
slurry is indeed a potent fertilizer; 2) how slurry can be used given the predominant mixed farming systems
in the Terai and Middle Hills of Nepal; 3} different ways of composting to ease transport to fields; and,
4) the most efficient and economical use of the slurry as a fertilizer. Research on the use of composted
slurry has also been incorporated in the proposal for BSP Phase III (SNV, 1996:38).

1.3. Objectives

1.3.1. Overall Objective

To review currently existing literature on the effect of digested slurry on crop production with a view to
prepare a comprehensive volume for use by slurry extension workers and biogas policy makers.

1.3.2. Specific Objectives

• To review literature pertaining to the effect of different forms (fresh, sun dried, composted)
of anaerobically digested slurry on crop production.
• To review heath and sanitation aspects of bioslurry utilization in crop production.
• To review literature on slurry treatment for use in crop production.

4. Scope

This review was confined to the effects of digested slurry on crop production in the existing agroeco
logical conditions and the prevailing socio-cultural milieus in Nepal and adjacent areas with similar
agroeco logical and socio-cultural environments. It did not deal with its effects on livestock
production, fisheries, poultry production, and piggery.

5. Methodology

5.2.1. Interviews

Persons involved in slurry extension and research in Nepal and India were interviewed.

5.2.2. Literature search

Literature search was done by visiting following institutions:

• APPROSC library
• Department of Agriculture library

3
• Division of Soil Science and Agricultural Chemistry, NARC, Khumaltar
• Department of Livestock Development
Library of the National Agriculture Research Council
• Library of the Institute of Agriculture and Animal Sciences, Rampur
• Lumle Agricultural Research Center and its library
• Pakhribas Agricultural Research Centre land its library
• BSP
• ICIMOD library and documentation center
• Library of Tata Energy Research Institute, New Delhi

4
 CHAPTER 2

NUTRIENT CONSTITUTION OF BIOSLURRY

2.1. Organic matter and plant nutrients

As the present context is the availability of plant nutrients from organic sources it is useful to briefly
discuss about the organic matter and how plants derive nutrients from it.

Though it is present in small quantities, organic matter has a major influence on the physical and
chemical properties of soils. As it breaks down, it releases nutrients in a form which can be taken up
by plants and crops. Organic matter also helps bind soil particles together, and improves its
waterholding capacity. And more importantly, it is responsible for the physical and ecological
stability of the soil.

When plant materials or animal manure is added to the soil, it does not stay in its original form for
long. It is immediately attacked by a host of different soil organisms and undergoes a complex series
of biochemical steps leading ultimately to its complete breakdown. The bulk of the material
undergoes an oxidation or burning' process in which the carbon and hydrogen which make up about
half of the dry weight of organic matter combine with oxygen to produce carbon dioxide and water.
Energy is released in the process, and this is what is used by bacteria and other soil microorganisms
for their survival and growth.

As the basic structure of the plant material is broken down (the breakdown may start from a series of
intermediary steps like the digestive system of living creatures and anaerobic fermentation process
or it may start from the soil itself if these materials are returned to the soil as such), nutrients such as
nitrogen, phosphorous, potash, sulphur, etc., are released from their original organic form. Part of
these may become soluble, and therefore be immediately available to growing plants. Most are,
however, taken up by microorganisms and stored in their tissues as they grow and multiply. These
are only released when original plant matter has been used up and the organisms themselves start to
die off and decompose. A variety of complex organic products accumulate in the soil as the process
of decomposition continues. These include lignins and other materials that are resistant to
decomposition as well as polymers derived from microbial products. This more or less stable
fraction is called humus. It is usually dark in colour and persists in soil for many years, degrading
very slowly but being replenished each year by the new additions of organic materials.

The breakdown of organic matter depends on a variety of soil and site conditions. Nutrient and pH
status, moisture content and temperature, and the availability of oxygen for soil microorganisms
affect the rate of breakdown of organic materials.

2.2. Nutrient supply

In traditional agricultural systems where very little or no chemical fertilisers are applied, breakdown
of organic materials supplies the dominant portion of nitrogen and sulphur needed by plants and as
much as half of the phosphorous (Bernard, 1985). Organic matter considerably enhances, the cation
exchange capacity of the soil - that is, its ability to bind positively charged ions such as magnesium,
calcium, potassium and ammonium. Without this binding effect, these nutrients would be rapidly
leached away when it rained. Cation exchange ability of the organic matter is particularly important
in acid soils, and those with low clay content since such soils have low binding ability. Organic
matter also forms complexes with micro nutrients such as iron, manganese, boron and copper and
through binding prevent them from being lost through leaching. Phosphorous availability is
increased with the presence of organic matter. This occurs when organic matter forms complexes

5
with amorphous ion in the soil thus preventing them from binding and immobilizing phosphate ions.
The pH range of the soil is an important condition for many chemical reactions and microbial
activities in soil. Organic matter helps buffer the soil pH by keeping it towards the neutral range.
This increases the availability of phosphorous, molybdate, borate, and a number of other nutrients.

2.3. Improvement in soil chemical, physical and biological properties

Organic matter helps to bind soil particles together into aggregates. This improves the physical
properties of the solid making it easier for roots to penetrate. Tillage becomes easier and soil
becomes well-drained. The binding effect also reduces wind and water erosion. With organic matter,
the water retention capacity of soil is also considerably increased.

2.4. The nitrogen cycle vis-a-vis organic matter

This brief description of the organic matter was provided to put the discussion and review on
nitrogen into proper perspective, because organic matter in soil is the reservoir of nitrogen, and
nitrogen is the most important of the nutrients that affect crop yields. Other nutrients like
phosphorous and potash are also important when growth rates are fast, but even for this the presence
of nitrogen is required. Micro nutrients have their own roles but are required in smaller amounts.

The following review will focus on nitrogen. General constitution of phosphorous and potash wiil
also be reviewed in fresh wet, sun dried slurries and slurry composts in the latter part of the chapter.

Nitrogen exists in two main forms in the soil. The major portion of it, usually more than 90%, is
present in an organic form, immobilized in the amines and other complex molecules that make up
soil organic matter. This ' organic nitrogen pool' represents a substantial store of nitrogen. It is
unavailable to plants, but is protected from being leached away when it rains. Only a small fraction
of the total soil nitrogen exists in soluble forms that can be used by plants, either as nitrate or
ammonium ions. Thus rather than the total nitrogen content of any organic matter, the proportion of
these ions determine crop growth.

The processes through which nitrogen is gained or lost in the soil forms a cycle known as the
nitrogen cycle7 ( Fig 1). Organic matter break-down constitutes one of the key pathways in this
cycle. As the organic matter decomposes in the soil a portion of nitrogen in the organic pool is
released into solution (mineralisation).

It has been estimated that 2.3% of the total organic nitrogen pool is mineralised each year (Brady
1974, cited in Barnard et al., 1985). The soil also receives small amounts of nitrogen from rain and
dust. Other important sources include the biological nitrogen fixation and, of course, nitrogen
fertilisers. Nitrogen losses from soil occurs through uptake by crops, leaching and soil erosion. A
certain amount is also lost in a gaseous form, either due to the action of ' denitrifying bacteria' which
converts nitrates to nitrous oxide and nitrogen, or through the volatilization of free ammonia. The
former is of relatively minor significance; the latter is only important in dry, alkaline soils which
have been treated with large amounts of urea or ammonia fertiliser (Barnard et al., 1985).

6
 Figure 1. Nitrogen Cycle In Farm Land

Source: Adapted from Gunnerson and Stuckey, 1986, reproduced in GATE, 1993:

7
2.5. Nutrient composition of biogas slurry in different forms

2.5.1. Overview of past research on anaerobic digestion

The production of combustible gas ('Marsh-gas' or * Will-o' the Wisp') from decaying organic
wastes in marshes and swamps has been known for a long time (Acharya, 1961:2). Laurie (1941)
reported that as early as 1778 Volta knew that the gas contained methane. Poppof in 1875, produced
hydrogen and methane from a mixture of river silt (mud) and materials containing cellulose
(APRBRTC, 1983:1). Martin-Leake and Howard (1952) reported that Louis Pasteur in 1884
presented a paper (by Gayan) on the production of methane from yard manure. Also early in 1866,
Bechamp, a student of Pasteur, was among the first to show definitely that the formation of methane
was a process of biology (APRBRTC, 1983:1) According to Waksman (1932), Omeliansky in 1902
pointed out that cellulstic material like filter paper if inoculated with horse-dung or river mud, along
with mineral salt solutions and kept under anaerobic conditions, evolution of gas took place. This
gas mainly contained methane and hydrogen. Thysen and Bunker (1927) reported that Omeliansky
also isolated two different types of bacteria: Bacterium methanigenes which produced methane and
Bacterium fossicularum which produced hydrogen. In fact he was the first to isolate methanobacteria
(not a pure strain though) in 1916 (APRBTC, 1983:1). In the beginning of the Twentieth Century,
the method of anaerobic fermentation or "digestion" was successfully applied by sewage chemists
(Acharya, 1961:2). In 1936, using chemically synthesized media to culture, Barker obtained a kind
of microorganism capable of producing alcohol, butanol, and propanol through fermentation
(APRBTC, 1983:1). A considerable amount of research work was carried out by sewage chemists on
different aspects of the digestion process and sludge digestion plants were installed at Birmingham,
Baltimore, Mogden and Bombay; the gas produced was used for operating machinery and for
lighting purposes (Haseltine, 1933 quoted by Acharya, 1961:2) and even for operating lorries and
tractors (ibid.)- However as Acharya (1952) reported, the application of the method to the materials,
other than sewage sludge, did not receive required attention. Such an attention for him was important
since huge quantity of farm waste could be utilized for gas production. In this context the studies of
Foroler and Joshi (1923) (anaerobic fermentation of newspaper, filter-paper, banana peels, etc.);
Keefer et al. (1934) Fair (1934) (anaerobic digestion of garbage), Nelson et at. (1939 ; 1940; 1942);
(digestion of chopped corn stalks, chopped seed-flax, artichoke, etc.), and Desai (1945) (cattle dung
and vegetable litter), are important. The works of Duceliar and Isman (1949), Duceliar (1950),
Isman (1950) (all on farm wastes), among many others, were important since combustible gas was
successfully produced in all those experiments. The works of Desai (1945; 1964), Patel (1951) and
Acharya (1953, 1958) are important ones in the Indian context as long as gas production and plant
design efforts are concerned.

From this background it is clear that the emphases up to 1950, were clearly on energy (gas).
Manurial aspects were generally not taken up as a matter of research. In fact during the course of
review it was revealed that the engineering and micro biological aspects of gas production remain a
dominant preoccupation to the 1990s.

2.5.2. Early research on manurial value of slurry

By the 1950s many researchers had already reported that manure production by anaerobic digestion
was more efficient in nitrogen conservation than aerobic methods (Acharya, 1961:8). Desai and
Biswas (1945, cited by Acharya, 1961: 8) obtained manure containing 1.7 percent nitrogen in the
dry matter and the manure showed better effect on crops than from yard manure. According to an
account furnished by Rosenberg (1952a, cited by Acharya, 1961:4) an experiment was carried out
by H. Hisserich in Germany and to discuss it a special conference was held at Ludwigsburg in 1947.
As a result of the deliberations in the conference, a large-sized mechanized biological gas plant was
set-up at Allerhorp in the Luneberg Health area. The experiment with anaerobicaiiy digested
manure showed that it gave higher yields than ordinary farm yard manure. This led Martin-Leake

8
and Howard (1952a, quoted in Acharya, 1961:4) to remark: "The Luneberg Health is notoriously
one of the most hopeless agricultural tracts in Europe. It is claimed that after four or five years'
application of the Allerhorp residual tank manure, the sugar-beet crop compared favourably with
what could be grown on the best soils in Germany." The Allerhorp experiments also found that the
manure was specially valuable oh light soil like that at Luneberg Health (Germany) and produced
good effect on crops like potatoes, vegetables and tomatoes. In order to obtain good quality manure
without loss of nitrogen, along with good gas production, the experimenters recommended digestion
to an extent of 30 percent of the organic matter or 22.5 percent of the dry matter (Rosenberg, 1952
cited in Acharya, 1961:8).

The earlier days of attributing fertilizing value to biogas slurry (and up to some extend today) was
largely based on laboratory studies and isolated observations of crop performance rather than
serious research into the nutrient composition of bioslurry in different forms and the subsequent
effects on crop performance.

2.5.3. Contemporary research on nutrient constitution of biogas slurry

It is obvious that biogas generation is technically feasible through the anaerobic digestion of a
variety of organic materials. In India, China and Nepal, however, animal and human faecal matter
are the dominant inputs for the production of biogas. During the anaerobic fermentation process
about 25 to 30 percent of the organic matter from the faecal matter is converted into biogas while
the rest becomes available as a residual manure (Chawla, 1986) which is generally considered to the
rich in major plant nutrients (NPK) as well as in micro nutrients such as zinc, iron, manganese and
copper, which are generally in short supply in many soils (Tripathi, 1993:10).

Nitrogen as a fertilizer is consumed in the largest quantity. Therefore its provision through organic
sources, residues, chemical fertilizer, is of enormous importance to agriculture. Because of this, its
presence both in the animal waste and the digested slurry and the examination of literature on
whether loss of nitrogen occurs during the process of anaerobic digestion for obtaining combustible
gas is of direct relevance to the study. In India (Acharya 1961:1 5) has reported that during the
process of anaerobic fermentation of bullock dung, about 1 5 percent of the total nitrogen contained
in the dung converted into the ammoniacal form and that almost the whole of the ammonia formed
remained in solution in the digested slurry. Acharya (1961:17-18) has also reported the results of
another set of experiment that measured the formation of ammonia during anaerobic digestion of
bullock dung. The experiment showed that digested dung slurry contained 12 to 18 percent of its
total nitrogen in ammoniacal form. The pH measurement carried out on the digested slurry showed
values ranging from 8.0 to 8.4.

Acharya (1961:17) also reported that on drying the digested cow dung slurry, around 96 percent of
the dissolved ammonia escaped into the air. In order to explain this loss a measurement of pH before
and after the fermentation was made and was found to be 7.2 and 8.3 respectively. The increased
alkalinity was presumed to be due to the accumulation of ammonia in the slurry after digestion. Due
to the alkaline pH, almost the whole of the ammonia present was lost by volatilisation during the
evaporation and drying of the digested slurry* (Acharya, 1961:17; Chawla, 1984:109). The dried
residue contained only 1.78 percent of nitrogen. If there was no loss of ammoniacal nitrogen, the
total nitrogen would have come to around 2.16 percent of the dry matter.

In another experiment Acharya (1961:17) again found that during the sun drying operation, the
manure lost nitrogen roughly equivalent to the whole of free ammonia present. Analysts of the
residue left after sun drying showed only very small recoveries of ammonia.

The nutrient constitution of biogas slurry vary from site to site. And the factors affecting this
constitution range from the type of fodder being eaten by the livestock to the type of organic
biomass fed to the digester. Table 3 and 4 present examples of variations in the constitution of

9
various materials used in the digestion.

Table 3: Total solid content (dry matter) of fermentation materials commonly used in rural
areas (approximation)
Materials Dry matter content (%) Water content (%)
Dry rice straw 83 17
Dry wheat straw 82 18
Maize stem 80 20
Green grass 24 76
Human excrement 20 80
Pig dung 18 82
Cow Dung 17 83
Human urine 0.4 99.6
Pig urine 0.4 99.6
Cow urine 0.6 99.4
Source: APRBRTC, 1983:46

Table 4: Carbon: nitrogen ratio of feedstock commonly adopted (approximation]

Feedstock Carbon content of Nitrogen content of Carbon: Nitrogen
feedstock by weight (%) feedstock by weight (%) ratio (%)
Dry wheat straw 46 0.53 87:1
Dry rice straw 42 0.61 67:1
Corn stalk 40 0.75 53:1
Dead leaves 41 1.00 41:1
Soybean stalk 41 1.30 32:!
Grass 14 0.54 27:1
Peanut
Stalk and leaves 11 0.59 19:1
Fresh sheep dung 16 0.55 29:1
Fresh cow dung 7.3 0.29 25:1
Fresh horse dung 10 0.42 24:1
Fresh pig dung 7.8 0.60 13:1
Fresh human dung 2.5 0.85 2.9:1
Source: APRBRTC, 1983:45

Reports on nutrients are often vague due to the fact that researchers often do not bother to
mention the sources, methods and modes of analysis. It is thus usual not find whether a
particular nutrient data were generated on volume/volume or weight/weight or dry/dry basis.
Table 5 to 1 7 below present a glimpse of the nutrient composition of different forms of organic
manure as reported by different authors. Different authors report different data based on their
circumstances. The data presented below are not exhaustive and are meant to provide a " feel' of
the situation.

10
Table 5 : NPK values of fresh cow dung slurry
N% P2O5% K2O% Author
1.00-1.80 0.8-1.2 0.8-1.00 (0.9) Gupta, 1991
(1-4) (2)
1.5-2.0 1.0 1.0 Tripathi, 1993
(1.75)
1.30 0.82 1.07 Gupta, 1991
1.25-1.30 Chowla, 1986
(1.28)
1.51 Naear. 1975 in Kuppuswamy, 1993
1.8-1.9 Acharya, 1961
(1.85)
1.4-1.8 1.1-2.0 0.8-1.2 Gitanjali et al. in Gupta 1991
(1.6) (1.55) (D
1.30-2.50 0.90-1.90(1. Myles et al., 1993
(1.9)
1.4-1.8 1.0-2.0 0.8-1.2 DOST, Govt of India, 1981
(1.6) (1.5) (t.0)
1.5-2.0 1.0 1.0 Khandelwal et al., 1986
(1.75)
0.5-1.0 0.5-0.8 0.65 0.6-1.5 (!.05) Demont et al, 1990
(0.75)
Figures in parenthesis indicate average

Table 6 : Composition of spent slurry from nightsoil biogas plants

N% P% K% Author
3.25 1.00 0.83 Kaulet-al;, 1986
3.0-5.0 2.5-4.4 0.7-1.9 Khandewai, 1986
(4.0) (3.45) (1-3)
Figures in parenthesis indicate average

Table 7: NPK content of sun -dried bioslurry

N% p% K% Author
1.60 1.40 1.20 Gitanjali et. al. in
0.5-1.0 0.5-0.8 0.6-1.5 Demont et al. 1991
(0.75) (0.65) (1.05)
1.00 0.23 0.84 Gupta, 1991
Figures in parenthesis indicate average

Table 8: NPK content of bioslurry and FYM

N% P% K% Author
Composted bioslurry 0.5-1.0 0.5-0.8 0.6-1.5 Demont et al., 1991
(0.75) (0.65) (1.05)
FYM 0.6 0.25 0.55 Gupta, 1991
Figures in parenthesis indicate average

11
Table 9 Quality and composition of human faeces and urine*
Approximate quantity Faeces Urine
Water content in the nightsoil per 135-270 gram 1.0-1.3 litre
capita
Dry wt, per capita 35-70 gram 50-70 gram
Approximate Composition (Dry
Basis)
Moisture, % 66-80 93-96
Solids 20-34 4-7
Composition of Solids
• organic matter, % 88-97 65-85
• Nitrogen (N), % 5-7 15-19
• Potassium (K), % 0.83-2.1 2.6-3.6
• Carbon, % 40-55 11-17
• Calcium (Ca), % 2.9-3.6 3.3-4.4
• C/N ratio 5-!0 0.6-1.1
Source: Satyanarayana et. al., 1986:11 * Phosphorous Is conspicuously absent in the. report

Table 10: Characteristics of nightsoil

Parameters (Dry basis} Average Values
PH 5.2-5.6
Moisture % 86.7
Total Solids, % 13.3
Volatile Solids, % 11.6
• Total Nitrogen (N) % 4.0
• Total Phosphorus (P), % 1.53
• Potassium (K), % 1.08
Source: Sacyanar3yana et. al., 1986:11

Table 11: Manurial value of slurry and other characteristics of human excreta fed to biogas
digesters.
Parameters Value
Gas production capacity/day 0.025 m3
Methane, % 60-65
Carbon-di-oxide, % 30-35
Hydrogen Sulphide, % 0.05-0.10
Fuel Value, K cal/ m3 5600-6500
Quantity of sludge produced 0.71 Litres wet/capita per day with 5% total solids
Manurial value of sludge 3.25
• Nitrogen, % 1.00
• Phosphorous, % 0.83
• Potassium, %

Source: Satyanarayana et. al., 1986:17

12
 Table 12: Average composition of nightsoil and urine

Item Faeces Urine

Moisture (%) 70-85 93-96
Organic matter (% dry wt.) 88-87 65-85
Nitrogen (%) 5-7 15-19
P,O, {%) 3-5.4 2.5-5
K7O {%) 1-2.5 3-4.5
CaO (%) 4.5 4.5-6
Source: Gaur et at., 1986:106

Table 13: Composition of spent slurry from nightsoil biogas plant

Item Percent on dry weigh basis
Nitrogen 3.0-5.0
P2O5 2.5-4.4
K2O 0.7-1.9
Source: Gaur, et at, 1986:107

Table 14: Effect of digester manure on physical and chemical properties of Soil
Location Treatment pH Organic Total Total Available Volume Porosity
3
matter nitrogen (P2O5) (P2O5) WL gm/c (%)
(%) (%) (%) ppm
Chyu- 1. Check 6.85 1.040 0.064 0.096 13.2 1.44 45.66
county (2 2. Digester
years) Sludge 6.80 1.210 0.068 0.110 14.4 1.41 46.59
3. Increase 0.1 7% 0.004% 0.014% 1.2 -0.03 0.93%
Dayi- 1. Check 8.30 1.035 0.071 0.109 16.3 1.27 52.59
County 2. Digester
(1 y«r) Sludge 8.35 1.286 0.101 0.1 10 0.04 1.16 57.35
3. Increase 0.25% 0.03% 0.001% 4.1* -0.11 4.76%
Source: APRBRTC, 1983:160 * the increased ppm should have been -16.24 which means
that the available P2O5 was reduced with the application of digester sludge in this location. The
report is however a preliminary one.
Table 1 5: Comparison of loss of nitrogen between digester manure and
farmyard manure
Treatment Total Nitrogen Ammoniacal Nitrogen
Jin % Jin %
Before treatment 0.950 !00 0.168 100
Digester manure 0.940 98.9 0.438 260.7*
Open air pool manure 0.646 68.0 0.138 82.1
Compost 0.572 60.2 0.0301 17.9
Source: APRBRTC, 1983:1 55 i jin= 1/2 kg * Ammoniacal nitrogen increased to 260.7% from
100% in the manure before digester treatment (an increase by more than 1.6 times)

13
 Table 16: Approximate range of nutrient contents of digester manure
Digester Organic matter Humic acid (%} Total nitrogen Total Phosphorus Total potassium
(%) (%} (P2O5) (%) (K2O) (%)
Effluent ----- ----- 0.03-0.08 0.02-0.06 0.5-0.10
Sludge* 30-50 10-20 0.8 -1.5 0.4 -0.6 0.6-1.2
Source: APRBRTC, 1983:155. 'Settled, more solid portion of the slurry Table 17: Average
constitution of fresh dung, dung slurry, digested slurry

Table 17: Average constitution of fresh dung, dung slurry, digested slurry*

Fresh dung Dung mixed with water Slurry

g/kg % wet % dry g/2kg % wet %dry g/2kg % wet % dry
base base base base base base
Water 800 80 ---- 1800 90 - 1820 93
Dry matter 200 20 100 200 10 100 140 7 100
Organic 150 15 75 150 7.5 75 90 4.5 64
Inorganic 50 5 25 50 2.5 25 , 50 2.5 Z6
Total Nitrogen 5 .5 2.50 5 .25 2.5 5 .25 3.60
Mineral 1 .10 .50 1 .05 .50 2 .10 1.40
Organic 4 .40 2 4 .20 2 3 .15 2.2
Phosphorus 2.50 .25 1.25 2.50 .13 .25 2.5 .13 1.80
Potassium 5 .50 2.50 5 .25 2.50 5 .25 3.60
Total 1000 100 - 2000 100 - I960 100 -
Source: Van Nes, undated: 4 * Based on calculations

Broad conclusions can be drawn from these tables. Theoretically sun-dried slurry should provide a
lower percentage of nitrogen as around 90% of the ammoniacal form of nitrogen is generally
accepted to be volatilised during the sun drying process. But as the tables show the data provided
from the different sources are not that much consistent. However more of the reports show higher
available N content in fresh bioslurry than in sun-dried slurry. Also nutrient content is reportedly
higher in the sludge (settled, more solid portion of the slurry) than in the liquid effluent
{supernatant, liquid portion of the slurry which collects at the surface). Bioslurry derived from
human excreta contains the higher proportion of nitrogen than any form of organic manure reported
in these tables. Composted bioslurry is found to contain higher proportions of NPK than FYM
Similarly digested slurry also contains higher amount of mineral nitrogen than fresh dung and dung
mixed with water. It is also evident that both fresh cow dung and non-digested dung slurry contain
higher proportion of organic nitrogen than digested slurry indicating the conversion of organic
nitrogen to more available forms during the process of anaerobic fermentation. No differences are
evident in the proportion of potassium and phosphorous contents in these three forms of organic
fertilizers.

Similarly there are also many reports indicating the superior manurial value of composted slurry
over ordinary composts (Demont et al., 1991 inter alia).

A recent report (ATC,1997) on the constitutions of slurry compost, fresh and sun- dried slurry and
fresh cow dung by a laboratory in Nepal furnishes the following data:

14
 Table 18.a. : Average constitutions of different forms of organic manures from samples collected
from different parts of Nepal
Particulars PH Moisture Total Organic C:N Phosphorous Potassium Remarks
(%) Nitrogen Matter P2OS % K20 %
(%) (%)
Compost 7.8 2 65.02 1.31 25.07 11 1.18 0.88 Wet basis
3.75 71.70 11 3.37 2.52 Dry basis

Sun-dried 7.4 4 40.66 1.73 24.53 8 0.69 0.68 Wet basis

slurry 2.92 41.46 8 1.17 1.15 Dry basis

Fresh dung 8.1 1 81.25 0.30 15.47 30 0.78 0.42 Wet basis
1.60 82.46 30 4.16 2.24 Dry basis
Fresh slurry 7.1 6 93.07 0.06 4.55 44 0.04 0.06 Wet basis
0.87 65.66 44 0.58 0.87 Dry basis

Source: ATC, 1997

In brief, following points can be noted in terms of manurial values of these forms of manures as
reported in this analysis.

As against the theoretical premise and data from India, estimated NPK values of fresh slurry reported
are too low. Also as against so many of the published data, the higher NPK values in sun-dried slurry
is difficult to explain. The nitrogen content of sun-dried slurry even exceeds that of the bioslurry
compost.

The NPK values of bioslurry compost is excessively high as compared to published data and exceeds
those values reported for the fresh slurry in exceptional ways. Higher NPK values of bioslurry
compost vis-a-vis ordinary compost or even sun-dried slurry can be explained but the reported values
exceed the NPK values of fresh slurry. The data indicate the sun-dried slurry is superior in terms of
nitrogen to all the three categories of manure (bioslurry compost, fresh dung and fresh slurry) on wet
basis. On dry basis slurry compost is shown to be superior to other forms in terms of nitrogen
content. On both dry and wet bases, fresh slurry is shown to fall at the bottom in terms of nitrogen
content. This is not only in the case of nitrogen, fresh slurry is also shown to contain the lowest
amount of both phosphorous and potassium among these four types of organic manures. These
reports cannot be explained on the basis of what has been generally said about the fresh biogas slurry
in biogas literature. Perhaps the sampling techniques themselves have to do something with these
results. The measurement difficulties in the determination of manurial values of different organic
manures have been discussed elsewhere in this review.

ATC (1997) has also reported the results of analysis of samples of chicken dropping, cattle,
buffalo and pig dungs collected from various parts of Nepal. Table 18b presents data from this
analysis.

15
Table 18.b. : Average constitutions of fresh chicken dropping and fresh cattle, buffalo, and pig dung
from samples collected from different parts of Nepal
Particulars PH Moisture Total Organic C:N Phosphorous Potassium Remarks
(%) Nitrogen Matter P2OS % K20 %
(%) (%)
Cattle and 8.11 81.50 0.26 14.88 33 0.77 0.39 Wet basis
Buffalo 1.41 80.50 33 4.17 2.11 Dry basis
Chicken 7.35 42.60 2.05 43.34 12 1.07 1.0 Wet basis
3.57 75.41 12 1.86 1.74 Dry basis
Pig 7.3 60.15 0.59 15.64 15 0.89 I.I 1 Wet basis
1.48 39.26 15 2.23 2.79 Dry basis

Source: ATC, 1997

Table 18b above shows that, as usual, chicken dropping contains the highest amount of total
nitrogen. This has shown to be so on both wet and dry bases. Chicken dropping is followed by pig
dung in terms of the amount of total nitrogen content. However, on dry basis, both pig and cattie +
buffalo dungs showed higher amount of phosphorous and potassium content.
ATC (1997) also analysed fresh slurry samples from biogas plants with and without toilet
attachment. Table 18c below presents comparative data on these two types of fresh slurry.
Table 18.c. : Average constitutions of fresh slurry from biogas plants with and without
toilet attachment
Particulars PH Moisture Total Organic C:N Phosphorous Potassium Remarks
(%) Nitrogen Matter P2OS % K20 %
(%) (%)
Without toilet 7.1 93.83 0.054 4.54 48 0.040 0.066 Wet basis
attachment 2 0.875 73.59 48 0.648 1.070 Dry basis
With toilet 7.2 92.32 0.065 4.555 40 0.039 0.064 Wet basis
attachment 0 0.864 59.306 40 0.508 0.833 Dry basis
Source: ATC, 1997
In terms of NPK values, no pronounced differences between fresh slurries from biogas plants with or
without toilet attachment are observable. This may due to the relatively lower amount of human
excreta (as compared to cattle and buffalo dung) fed to the biomass plants.
2.5.4. Nitrification studies and the issues of nitrogen conservation in digested slurry

Table 18d: Nitrification of digested slurry

Manure treatment NO] found after Mean value Excess over soil Percentage of added
3 months (mg.) (mg.) only (mg) manure N Nitrified
Soil only 6.90 7.20 -
(duplicate) 7.50
Soil plus digested 11.25 11.63 4.43 7.38
slurry (duplicate) 12.00
Soil plus farm yard 10.20 10.05 2.85 4.75
manure (duplicate) 9.90
Soil plus ammonium 21.00 20.25 13.05 87.00
(duplicate) 19.50
Source: Acharya: 1961:29

16
Acharya's nitrification studies showed that digested slurry was somewhat superior to farm yard
manure in regard to its nitrifiability in the soil, a reconfirmation of the conclusion of an earlier
(Desai et al. 1945) study of nitrification.

Nitrification studies with similar results is also reported by Chawla (1984) after a couple of
decades later.

Table 19.a. : Nitrification of digested slurry

Treatment mg NC3 per 100 g Soil Percent of manure N nitrified

Soil 5.3 ...
Soil + Wet Slurry 11.7 21.3
Soil + Dry Slurry 10.9 18.6
Soil + Compost 10.2 16.3
Source: Chawla, 1984:110

Table 19 shows that fresh digested slurry nitrified to the extent of 21.3 percent compared to 16.3
percent mineralisation of compost nitrogen. Sun dried slurry nitrified to the extent of 18.6 percent.
This has to be so due to the loss of ammoniacal nitrogen. This finding along with Acharya (1961)
and Desai et al. (1945) shows the advantage of anaerobically digested slurry and thus provide a
sound basis for slurry extension educational programs.

On the whole, these sets of experiments suggest that the process of anaerobic digestion possesses a
double advantage, i.e., the process, in addition to providing a good quality manure also supplies a
large volume of combustible gas. (Anaerobic fermentation in the biogas digester does not result in
any absolute increase in the nitrogen content of the slurry; the relative increase is noticed due to the
loss of 25 to 30 percent of the loss of organic matter of the dung during biogas generation (Kate,
1991:9; Gupta, 1991:22). It has been reported that in India the total nitrogen content of the dung
rarely exceeds 1 percent due to poor quality of the animal diet, and hence, the nitrogen content
usually falls in the range of 1.25 to 1.30 percent. Others have reported slightly different ranges( e.g.,
Gupta , 1991:18, 1 to 1.8 percent; Maskey 1978:1, 1.6 to 2 percent etc.) These and similar other
experiments and arguments compel to believe that anaerobic digestion in general does not reduce the
amount of nitrogen.)

Acharya also reported a somewhat contradictory results from experiments conducted in large size
plants (1961:35-51). Crop experiments on wheat, sannhemp and marua ( Eleusine coracana) showed
that the digested slurry in wet condition did not produce good manurial effect as after sun-drying.
The laboratory results discussed above had shown that the digested slurry in wet condition contained
about 16 percent of its nitrogen in the form of readily available ammonia whereas the dried slurry
contained very little of ammonia and was lower In total nitrogen. It has been suggested that the
poorer effect shown by the wet slurry on all the crops examined may be due to some harmful factors
to plant growth, possibly H2S or other products of anaerobic digestion, present in the fresh slurry,
which are removed in the operation of sun-drying of manure (Acharya, 1961:51). A situation in
which wheat yield decreased due to the application of fresh biogas slurry Is also reported from
researches in Nepal (Maskey, 1978:3). For reasons unknown, the result has not been properly
verified. Sathianathan (1975 quoted by Maskey, 1978:3) has suggested that the high ammonia
content of fresh digested slurry could force large dose of N2 in plant and create excessive toxic
compounds. For this reason, it has been recommended to use slurry after a few weeks of collection
from the digester or compost it by mixing with other substances. The presence in fresh slurry, of
toxic compounds like H2S is also mentioned by Balmor et al. (1982:220). But they dismiss it as a
serious problem in Nepal because the cattle and buffalo dungs is the common feed for biogas plants

17
and treatment of slurry in such cases should not be a serious concern. Even if nitrogen fixing bacteria
have been detected in some systems (El-Haiwagi, 1980), the air-tight, anaerobic environment
precludes the possibilities of nitrogen fixation; however nitrogen is increased in the relative sense
due to the decomposition of organic matter and formation of gases and not due to formation of "new
nitrogen" (Gupta, 1991:22). An increase of total nitrogen is inconceivable since there is not known
process on nitrogen fixation' inside the digester (Tarn, et al. 1983:12).

Tarn et al. (1983) and Chawla (1984) are concerned about the 'inflated and exaggerated' reports of
increase in nitrogen content in the residual slurry. Tarn et al. also cites lanotti (1979), Institute of
Soil and Fertilizer of Sichuan China (1979) and Li (1982) in gathering the challenging evidence
against the importance of biogas slurry as fertilizer. Tarn (1983:12) citing these authors states that
the "nitrogen level does reduce during anaerobic digestion, and the degree of reduction ranges from
3 to 10 percent". However, no effort is made anywhere in his lengthy report to explain how this
amount of nitrogen is lost during anaerobic digestion. Tarn also argues that the evaluation of digester
slurry by measuring its nutrient composition immediately after it comes out of the digester is not
appropriate since storage time, transport distance and application method etc. have direct effect on a
benefit assessment of slurry as fertilizer. Vogtmann et al. (1978) has reported that nitrogen loss of
anaerobically digested manure that is ploughed four days after application varied from 15 to 19
percent depending on the climatic condition. This loss can be expected to be higher in the tropics.

Van Brakel (1980) is ambivalent, and at times openly critical, about the logic behind the promotion
of bioslurry as a superior manure. He raises some serious questions about the way the manurial value
of organic manures, in general, are assessed. According to him the assessment of the quality of
fertilizers from organic sources is a difficult task involving the following factors:

• the form in which the manure is available ( liquid content, size of solid particles)

• the way it is distributed in the soil

• the C:N ratio, the C:P ratio, the relative proportion of these two ratios , and the
presence of minerals

• the properties of the organic material in the manure, particularly the disposition to
mineralize and the amount and type of humic components

• the rain that falls after the manure application

• the temperature and the humidity after manure distribution in the soil which strongly
affect microbral activity in the soil (Van Brakel, 1980:103).

Van Brakel argues that even if these factors are supposedly kept under some sort of control, it is
virtually impossible to compare different ways of manure processing particularly when processing
times of the systems to be compared are different. Because of the variations in the properties of
excreta of animals, the manure should be obtained from the same animals at the same time. If the
processing time is different, argues Van Brakel, it is impossible to take due account of the factors
mentioned above. Together with the statistical fluctuations that are said to be inherent in these kinds
of measurements, concludes Van Brakel, " only very large and long research projects may lead to
any reliable conclusions for the ' average' situation (p. 103).

He raises a similar problem with the determination and interpretation of the C:N ratio, which is
commonly used as a general characteristic of the quality of organic manure, and suggests that even if
there is some ground for using this parameter, one needs to be cautious in its application: "other
things being equal, the C/N ratio may well have a different physiological effect depending on the
way the carbon and the nitrogen are bound. In general it will be positive if the nitrogen is easily
accessible (that is to say, that mineralization proceeds quickly. However if the manure contains large
18
quantity of easily decomposable carbon compounds, this may stimulate microbial activity in the soil
so much (in particular if it is warm an humid) that no nitrogen is left for the plants, unless the C/N
ratio is too low" (ibid). In addition it makes quite a difference at what stage of the manure processing
cycle the C/N ratio is determined.

These arguments are directly relevant for those who are involved in assessing the constitution of
biogas slurry. In addition to the methodological problem in assessing the manurial values of organic
manures, Van Brake!, in line with (Tarn, 1983), is not optimistic about the outcomes of slurry
promotion and extension. He believes that "manure processed anaerobically contains a larger amount
of nitrogen that is readily assimilated by plants" but the handling of slurry after it comes out of the
plant is a major problem in nutrient conservation, and concludes that "for small scale application of
anaerobic digestion { in rural areas where the digester should be cheap and simple to operate) there
are few possibilities of preventing nitrogen losses, and the alleged better preservation of nitrogen
cannot be advanced as an advantage of the anaerobic way of processing manure" (p. 105).

On the whole, these reviews reveal that there is relative increase of nitrogen during the anaerobic
digestion. Evidence of nitrogen losses during anaerobic digestion as claimed by some is difficult to
find in the literature. Indeed it seems that substantial nitrogen losses occur from the moment slurry is
taken out from the digester to the moment it is worked in the soil.

2.5.5. Other nutrients

Up to this stage the review has been mainly centred around nitrogen due to reasons explained
elsewhere. However slurry also provides available phosphorous and potassium and micronutrients
that are important but are required in smaller amounts. No detailed reviews are necessary on these
topics.

2.5.6. Bioslurry and the physical and biological qualities of soil

In addition to nutrient supply, bioslurry and its different forms improve the physical and biological
quality of soil. Bioslurry, in its different forms, is relatively free from foul smell, weed-seed and
phytopathogenic organisms (Tripathi, 1993). It also improve soil porosity and water holding
capacity (moisture retention capacity {Tripathi, 1993; Santosh et al., 1993, APRBRTC, 1983)).
Slurry has bulk and fibre to hold soil manure (Arnott, 1982:56). This is what may be called the anti-
erosion quality of humus. In addition numerous researchers have reported that soil microbiai
activities increase remarkably after bioslurry utilisation. Slurry provides energy to soil microflora
including the N fixing and P solublizing organisms (Lakshmanan, 1993:3). Bioslurry is also reported
to be free from weed seeds. More weed seeds are killed during digestion than during any other
manure processing system( Van Brake), 1980:106) .

Scheffer et al. have reported that 20-30 days is enough to destroy the viability of all weed seeds. It is
suggested that the free ammonia that is formed during anaerobic digestion poisons the seeds because
methane does not kill the seeds but inhibits their germination. Even if some of the weed seeds remain
viable after anaerobic digestion subsequent composting of biogas slurry (specially at thermophilic
temperature range) will destroy the viability of these remaining seeds (Price, undated: 137). Weeding
is generally an expensive operation in many parts of Nepal where fresh cattle dungs are used. The
weed elimination part can be seen as an important labour reducing aspect of bioslurry (even more so
if bioslurry is composted) in crop production, although no systematic studies were encountered about
this aspect during the review.

Chapter 3 deals with the effects of different forms of bioslurry on crop production.

19
 CHAPTER 3

EFFECTS OF BIOSLURRY ON CROP PRODUCTION

3.1. Background to the study of manurial value of bioslurry

A review of works in biogas technology by van Brakel (sub-titled "a critical review of the pre-
1970 literature7 ) published in 1980, stated that "not much work has been carried out on the
quality of the solid output of an anaerobic digester in terms of fertiliser value" (van Brakel,
1980:101). This remains largely true even for today if countries like China and India are
excluded from the statement. Even in India, the emphasis traditionally has largely been on
energy aspects of biogas technology (Singh, 1997, personal communication) as evidenced by
the important involvement of the Ministry of Non-Conventional Energy Sources (MNES) in
biogas technology development and promotion. Nonetheless, Indian Agricultural Research
Institute (IARI), India's premier research institution of that kind has given "occasional
attention" to the fertiliser value of cow dung, comparing anaerobic digestion with other types of
manure processing (Van Brakel, 1980:101). In fact, IARI is one of the four institutions
worldwide cited by Van Brakel in his review of pre-1970 literature on biogas technology, to
have "carried out work on a significant scale concerning this important aspect of the
evaluation of anaerobic digestion for agricultural waste processing {Van Brakel,, 1980:101) -
the others being studies in. the University of Gottingen and Braunschweing- Volkenrode and in
countries like Poland and the then USSR. In IARI anaerobic digestion was compared with other
types of manure processing. IARI reported that biproducts of anaerobic digestion had narrower
ON ratio (25) 3& compared to cow dung from farm yard manure (38) and the former gave
better crop yield than the latter. Nonetheless, Van Brakel notes that no general conclusions were
reached.

At the university of Gottingen, research was carried out (during the period 1950-55) on various
aspects of the outputs of the Atlerhop design when applied to the field. Nitrogen losses and balance
of other elements, during anaerobic digestion of manures and various vegetative wastes, were
studied. In addition, extent of weed and pathogen destruction during digestion were also studied.
Even if the Allerhop process and the manure out of it was positively assessed by many (better
availability of nitrogen by plane and relatively narrower C:N ratio than those reported for IARI
studies), the results did not seem to warrant any other conclusions than the output of the Allerhop
design is comparable to the out come of any other good manure processing system: (van Brakel,
1980:101).

At Branschweig - Votkenrode various designs of anaerobic digesters were studied for their
efficiency in presenting nitrogen losses. Field experiments were conducted to determine the quality
of the manure.

In Poland field experiments with anaerobically digested manure were carried out but "no definite
superiorities of the manure after methane fermentation over ordinary farm manure could be
established" (cited by van Brakel, 1980:101).

in the then USSR, the nitrogen assimilation of fermented sawdust was studied and the yield of oats
and sweet lupine was reported to have been increased.

3.2. Contemporary research

Although Acharya's (1961) report was examined in the preceding chapter, it is pertinent here to once
again discuss the report, especially the experiment on the effect of effect of biogas slurry and FYM
on crop production. The premise for doing so is that since "farmyard manure is generally prepared
by aerobic fermentation, whereas manure in the fuel gas plant by anaerobic digestion; and the quality
of the two products may vary" (Acharya, 1961:50). In a pot experiment, the two manures were
20
applied at the rate of 100 Ib. nitrogen per acre, four weeks before sowing. For comparison,
ammonium sulphate was also taken as one of the treatments. The dosage of ammonium sulphate was
maintained at 25 Ib. per acre [following Russell, 1950, cited by Acharya, (1961:50) according to
whom the availability of nitrogen in bulky manures is considered to be about 25 percent of that in
ammonium sulphate. It was an experiment with five replications. Table 19 below presents data from
this experiment.

Table 19b: Mean yield/pot of grain, straw of wheat and marua

(Eleusine coracona) and Total Dry Matter of sannhemp.
Treatment Wheat Marua Sannhemp

Grain Straw Grain Straw Total Dry Matter

No Manure 8.84 13.46 10.1 31.4 93.4
Digested Slurry in wet
condition 10.32 15.26 12.0 33.8 106.8
Digested Slurry in dry
condition 11.31 17.39 13.6 36.8 117.2
Farm yard manure 10.02 16.28 12.4 31.6 104.4
Ammonium sulphate 13.70 19.55 15.4 41.2 121.2
Source: Acharya, 1961:51
As was discussed in the preceding chapter, despite the finding that wet slurry which is reported
to contain around 16 percent of the nitrogen in the form of readily available ammonia (the dry
slurry, on the other hand, contain very little ammonia and lower total nitrogen), and despite the
usual claim chat "Maximum benefit is obtained when slurry is used in liquid form as it comes
out of plant (Khandeiwal, et al. 1986), the poor effect shown by wet slurry (the phenomenon will
also appear in experiments to be reviewed latter), despite the presumed working of toxic
materials like hydrogen sulphide and others, is an interesting and relevant area of systematic
investigation.
Maramba (1978:155) reports the result of an experiment in the Philippines in which the
feedstock incorporated with high percentages of wheat pollard which contained higher
phosphorous than either nitrogen or potassium. As Table 20 below shows, the treatment with 388
ml of effluent/1 sq. m of plot showed higher grain yield/plot than either the control or other
treatments.

Table 20: Plot fertilizer experiment

Maya Farms, Philippines
Treatment Mean Grain Yield/Plot (Grains)
Control 479.20
5714ml of Effluent 507.00
388 ml of Effluent 556.17
Ammonium Sulphate +
Disodium Phosphate +
Potassium Sulphate 542.72
(8 gm- 8 gm - 3 gm)
Source: Maramba, 1978:155
The above table shows that higher dose of effluent here is not superior as compared to the lower
dose as long as grain yield is concerned. Studies have shown that (Arnott, 1982; Sathianathan, 20
1978,.etc.) uncontrolled supply of nutrients, especially nitrogen may, depress crop yields. When
biogas sludge runs directly into rice fields there is a large increase in the growth of blue green algae.
These algae absorb nitrogen from the air, which is good for the crop. But if excessive supply of

21
sludge is not stopped halfway through the growth cycle of the rice, flower initiation is stopped. The
rice plants continue to grow, but the rice grains do not develop (Arnott, 1982:62; DOST, 1981:47)
reporting on the works done in the Indian Agriculture Research Institute (IARI) states that if slurry
is not dried, there is very little loss of nitrogen. There is also no loss of phosphorous, potassium and
other micronutrients. Mineralisation of organic nitrogen in liquid slurry is also reported to be
superior to that in sun-dried slurry and farmyard manure. (This is in line with the earlier studies of
Deshai and Biswas, 1945 and that of Acharya, 1961). The relatively lower nitrogen mineralisation in
sun dried slurry is attributed to poor dispersion of colloidal material resulting to increased resistance
to subsequent microbial decomposition Table 21 below presents data from the pot experiment
conducted at the IARI.

Table 21: Mean yield of rice (grain) and berseem (dry fodder)
Treatment Average of first three years Average of next two years
(yield: g/pot} ( yield: g/pot)
Rice Berseem Rice Berseem
Wet Slurry Dried 20.4 18.4 11.8 14.4
Slurry Farmyard 24.4 23.1 12.9 15.0
Manure 21.9 22.8 11.7 14.2

Source : DOST, Govt. of India, 198 1:4

Again as in Acharya (196 I), Maskey (1978), wet slurry shows poor performance as compared to
dried slurry despite the evidence that mineralisation of organic nitrogen in liquid slurry is superior
to that in sun dried slurry and also that most of the nitrogen in ammoniacal form is lost when fresh
slurry is sun dried.
3.2.1. Research in slurry utilization in crop production in Nepal
In Nepal, the first biogas plant was introduced by Father Saubolle, S.]. of St. Xavier's School as
early as 1955, serious thoughts were given only after the newly set up Energy Research and
Development Forum of Tribhuvan University recommended that biogas be considered as
alternative energy resource for Nepal (Fulford, 1985: 1.5-1.6). This resulted in the inclusion of
biogas programme in the Agriculture Year of 1975/76. Study of effect of slurry on crop
production was initiated at the Division of Soil Science and Agricultural Chemistry in Khumaltar,
and by 1978 a couple of preliminary reports came out {Maskey, 1978; Bhattarai et al., 1978). The
experiments were conducted in wheat and it was indicated that fresh effluents caused toxic effects
on wheat crop (Fulford, 1978:19 and personal communication with concerned researchers).
Maskey (1978) conducted a simple experiment to see the effect of dry and fresh biogas slurry on
wheat yield furnishes the following data:

Table 22: Effect of biogas slurry (dry and fresh on wheat yield)
Treatments Grain yield in kg/ha. Increment over
(Average of 3 Years) control kg/ha.,
I. Control 1288 —
2. Biogas Slurry (Dry) 1450 162
3. Biogas Slurry (Wet) 1842 554
4. 50% dry Slurry +
50% Chemical fertilizer 2706 1418
5. 75% dry Slurry +
25% Chemical Fertilizer 1744 456
6. Chemical Fertilizer 3503 2215
Source: Maskey, 1978:2

22
The table shows that biogas slurry was not superior in terms of its manurial value as compared to
either different combination of dry slurry and chemical fertilizer or chemical fertilizer alone. Dry
slurry showed the lowest increment in wheat yield, probably indicating the loss of nutrient during
the drying operation.

Maskey (1978) also reports the result of another experiment where the effect of biogas slurry on
wheat yield was compared with the effect of other locally available manures.

Table 23: Comparison of the effects of biogas slurry*and other manures on wheat yield.
Treatments N% P2 O s % K2O% Grain yield kg/ha Increment
(Average of 3 yrs) {kz/M
Control - - - 1550
Biogas Slurry 1.49 2.94 2.38 1783 233
Compost .93 .75 .50 2015 265
Poultry Manure 2.6 1.26 1.66 3782 2232
Fertilizer - - - 3301 1851
Source: Maskey 1978:2 * Although it is not explicitly mentioned in the report, implicitly, it seems to be fresh slurry

The table shows that the biogas slurry was not able to achieve higher incremental wheat yield as
compared to compost and poultry manure. Poultry manure, in fact gave the highest incremental yield
(even higher than that of chemical fertilizer). The researcher comments: "From these simple field
trials our observations do not confirm with the results other scientists found in other parts of the
world. There may be several factors which were not looked upon in detail during these trials....
"(Maskey, 1978: 2). Although this particular experiment did not furnish information on the form of
slurry used, the possible toxic effect of biogas slurry, presumably in its fresh liquid from, is noted
(Maskey, 1978:3), though the claim of toxicity is not verified by further research in Nepal. As
mentioned elsewhere, even if toxicity of fresh dung biogas slurry has been noted by a number of
authors abroad, Bulmer et at. (1985) note that this should not be a matter of concern in Nepal.

Besides wheat, the effects of biogas slurry (it used to be called "gobargas" slurry due to "gobar" or
dung being a predominant feedstock for biogas plants) on the yields of a number of crops were
studied (Maskey, 1978:3). The table below summaries the incremental yields of these crops.

Table 24: Effects of biogas slurry on paddy, tomato, cauliflower, French bean, wheat, and maize
Crops Yield t/ha Increment
Without slurry With slurry
Paddy 2.7 3.0 0.3
Tomato 15.0 17.8 2.8
Cauliflower 4.6 5.6 1.0
French 0.3 1.0 0.7
Bean 1.2 1.8 0.6
Wheat 1.7 2.7 1.0
Maize
Source: Maskey {1978:3)
It can be noted that all crops gave higher yield with biogas slurry. Again the report did not mention
the form of digested (fresh liquid slurry, wet slurry, dried slurry, residual sludge) of slurry and the
type of feedstock fed to the biogas plant. In addition, the report is silent about the mode of
experiment. If as in Tarn's argument (1983) "without slurry7' was meant to be without any kind of
manure, then one is not sure whether or not such increment could also be achieved by other
manures. In this sense, the experiment is meaningless.

23
In another experiment, Bhattarai (1978) reports that biogas slurry when "applied directly"
"depressed" wheat yield in Bhairahawa Agriculture Station, while such a "depressing effect" was not
observed in Khumaltar. She noted that the effluent probably was not fully decomposed. In order to
look into these matters, an experiment was designed for irrigated and rainfed condition incorporating
5 treatments (control, wet slurry, dry slurry, 50% dry slurry + 50% chemical fertilizer and chemical
fertilizer (usual dose). The crop was wheat (RR 21). The data are presented below:

Table 25: Effect of biogas slurry on wheat yield under irrigated and rainfed conditions
Treatment Irrigated (yield:kg/ha) Rainfed (yield:kg/ha)
1. Control 1450 1450
2. Dry Slurry 1750 1600
3. Wet Slurry 1560 1750
4. 50% Chem. Fertilizer
+ 50% Dry Slurry 3800 2750
5. Chemical Fertilizer
(Usual Dose) 5700 4200
Source: Bhattarai (1978:2)
Earlier it was reported that wet biogas slurry had higher manurial value than that of dry slurry as
long as wheat crop was concerned (Maskey, 1978). But the manurial value of slurry was reported to
be lower than that of compost. The data on the above table show that dry slurry gave better wheat
yield than wet slurry under irrigated condition. Under rainfed condition, wet slurry gave higher yield
than dry slurry. It is probably due to the fact that wet slurry also provides moisture which is an
important factor in rainfed condition. As usual, the chemical fertilizer and the combination of
chemical fertilizer and dry slurry gave far more higher yields than slurry in wet and dry forms.

Again, the incorporation of compost, as one of the treatments in the experimental design, could have
provided a realistic picture, as the purpose generally was not to compare yield with chemical
fertilizer but with other sources of organic manure.

Bhattarai and Maskey (1988) also reports the result of research on the effect of azotobactor
inoculation in the different sources of organic manure including biogas slurry on the grain yield of
wheat at Khumaltar Agronomy Farm.

Table 26: Effect of azotobactor inoculation of biogas slurry and other compost manures on
wheat yield
Treatment N-P-K Year Grain yield of Wheat Increment Percentage
(kg/ha) (kg/ha) (kg/ha) increment
With Without
Aiotobact Azotobactor
or
Control 1976 2325 2569
1977 1550 1162
-40-30 1978 930 930 54.00 3.771
Mean 1603.33 1553

Biogas Slurry 1976 2650 2850

1977 2400 1700
100-40-30 1978 1300 1080 240.00 12.788
Mean 2116.66 1876.66

24
Poultry 1976 3175 2350
Manure 1977 2112 1537
100-40-30 1978 1600 1450 516.66 29.042
Mean 2295.66 1779.00
Compost 1976 3300 3025
100-40-30 1977 5065 5117
1978 3980 3730
Mean 4098.30 3957.33 141.00 3.563
Fertilizer 1976 ------ 2625
100-40-30 1977 ------ 4287
1978 ------ 2930 ------ ------
Mean ------ 3280.66
Source: Bhactarai and Maskey (1988:81-85)

Azotobactor inoculation in biogas during with 100-40-30 chemical fertilizer gave a mean wheat
grain yield of 2116.66 kg/ha. This is lower than that given by poultry manure and far lower than that
given by compost both with azotobactor inoculation with the same amount of chemical fertilizer.
These few researches on the manurial value of biogas slurry in Nepal provide a confusing array of
signals on the superiority and inferiority of biogas slurry over other organic manures. The superiority
of compost demonstrated so far goes against the argument that nutrient, especially nitrogen,
preservation is better in anaerobic digestion and that aerobic composting is inferior in this kind of
nutrient preservation. A number of points should be noted in this context. These researches were not
well designed. Different forms of slurry have different levels of nutrient contents. In most cases, the
experiments did not even mention the form of slurry used. In addition, the time span between the
removal of slurry from the digester and its ultimate use in the experiment is not mentioned in all of
these experiments. Nutrient loss can occur in this time span. Furthermore, the method of application
is important. For example, if slurry is left in the field exposed for a long time without ploughing or
without covering by soil, significant amount of nitrogen is lost. The storage practice is similarly
important. An exposed slurry pit is obviously not desirable from the point of view of nutrient
conservation. "Stilt worse, comparing the yields oV wops appftfcd *«Wh dlgestM %ffVa%Tii
*Mfah tVitat crops non. rettfctag vttf form ctf fanflhgr fc practically meaningless" (Tarn, 1983:13).
Research into the effect of biogas slurry on crop production has a long way to go. The research
works initiated in Nepal in the mid-seventies failed to get momentum; and after few insignificant
reports, research activities in this area ceased to exist within a couple of years.
3.2.2. Research in slurry utilization in other countries
In Poland, Kuszelewski et al. compared anaerobic and aerobic manure processing and found that,
beyond any doubt, anaerobic digestion reduced nitrogen loss, and nitrogen was more easily
assimilated. However in both pot and field experiments no difference in yield was found (cited in
Van Brakel, 1980:105). Van Brake! reports that the farmers' reports maintained in, Italy, France, and
a number of tropical countries are favourable with respect to the manurial qualities of anaerobic
sludge. However he suggests that % there may be some bias in these reports7 (ibid). His critical
perusal of the yield reports compels him to say: " .. it is doubtful whether any significant differences
in crop yield between various manure processing methods have been established' (ibid). He opines
that "as far as there are any differences, one may expect that they are different for different boundary
conditions and different crops, because of the interrelated influence of the presence of nitrogen,
phosphorous, and other elements, coming out differently for different crops" and cites the reports of
Sen et al. in which yield reportedly improved in pea but not in rice. "This may be explained with
reference to the amount of available phosphorus in the soil and the extent to which nitrification will
occur in the soil" (p.106).
Cott (1984) reports that mushrooms, cucumbers, tomatoes, when grown in the digester solid, did not
provide good growth medium the first year, but the following year, yields were surprisingly high.

25
Cott noted that this could substantially reduce investment in anaerobic digestion by shortening pay-
back time. This could also reduce fertiliser costs and costs involved in post-anaerobic treatment of
slurry in addition to neutralizing costs for peat.
Although earliest documented attempts to develop biogas technology in India can be traced back to
the early 20th century (1900-1920) (Moulik, 1990:11), concerns with slurry utilization for crop
production is a relatively recent development. Large scale slurry study programmes began only after
the 1980s. Dhussa (1985:25-29) compiled the results of some of the experiments, conducted up to
the mid-eighties, on the effects of biogas plant effluent on the yield of rice, wheat, maize, cotton,
cucumber, tomato, mungbean, and sunflower.
Table 27: Comparison of the effect of effluent and FYM on the yield of rice, maize,
wheat, and cotton
Crop Yields: kg/ha Incremental yield
Digester FYM Kg %
Rice Effl 634.4
t 597.5 38.9 6.5
Maize 555.9 510.4 45.5 8.9
Wheat 450.0 390.5 59.5 15.2
Cotton 154.5 133.5 21.5 15.7
Source: Idnani et al., 1974, cited in Dhussa, 1986:1 1 4
The effluent application gave higher yields in all the crops under consideration. The difference
between biogas effluent and FYM was manifested in a comparatively more pronounced way in
the case of wheat and cotton yield.
Table 28: Comparative yields of cucumber for varying quantities of effluent vis-a- vis
chemical fertilizer
Treatment Average yield/pot (kg)
Control A (No manure or fertilizer) 3.70
Control B (Recommended quantity of fertilizer) 6.78
Slurry @ 5t/ha 3.20
Slurry @ 1 Ot/ha 4.57
Slurry @l5t/ha 7.36
Slurry @20t/ha 6.20
Source: Clarita et al., 1982, cited in Dhussa, 1986:1 14
The cable shows that biogas slurry applied at the rate of 15 t/ha gave the highest grain yield, higher
even than the recommended dose of chemical fertilizer.
Table 29: Comparative effects of different doses of slurry and slurry-chemical fertilizer
combinations on tomato production
Treatment Yield: t/ha % Increase over
Control 26.12 C -t l
Fertilizer @ 90-120-60 kg/ha NPK 61.02 133.61
Slurry @ 5 t/ha 34.34 31.47
Slurry @ 10 t/ha 37.69 44.29
Slurry @ 1 5 t/ha 40.53 55.17
Slurry @ 20 t/ha 42.74 63.63
Slurry @ 5 t/ha + NPK @ 45-60-30 kg/ha 47.33 81.20
Slurry @ 10 t/ha + NPK @ 45-60-30 kg/ha 47.53 81.97
Slurry @ 15 t/ha +NPK @ 45-60-30 kg/ha 49.12 88.06
Slurry @ 20 t/ha + NPK @ 45-60-30 k?/ha 54.56 108.88
Source: Clarita et al., 1982, cited in Dhussa, 1986:1 14

26
Half dose of fertilizer with 15 and 20 t/ha gave relatively higher yields, but then, these yields were
out-performed by the treatment with full dose of chemical fertilizer.
Table 30: Effect of biogas slurry with and without mineral fertilizer on mungbean yield
Treatment Computed Yield % Increase over
(kg/ha) Control
Control 764.77 -
NPK @ 30-60-0 kg/ha 921.50 22.25
Slurry @ 5 t/ha 756.75 0.25
Slurry @ 10 t/ha 780.38 3.38
Slurry @ 1 5 t/ha 774.38 2.60
Slurry @ 20 t/ha 875.25 15.95
Slurry @ 5 t/ha + NP @ 15-30 kg/ha 796.12 5.46
Slurry @ 10 t/ha + NP @ 15-30 kg/ha 820.50 8.70
Slurry @ 15 t/ha + NP @ 1 5-30 kg/ha 821.25 8.80
Slurry @ 20 t/ha + NP @ 15-30 kg/ha 869.25 15.14
Source: Clarita et al., 1982, cited in Dhussa, 1986:1 15

The above table presents data on yields of mungbean obtained from various levels of effluent alone
and with half the recommended quantity of NPK. The comparison of these yields with that
obtained from the application of full dose of NPK shows that the effect of low level of effluent
application is insignificant. The treatment with 20 t/ha of effluent with or without NPK has given
the same yield . "It may be concluded that the leguminous crops don't respond well to the
application of manures" (Dhussa, 1985:26). However, as wifl be seen in other experiments,
leguminous crops like peas also did well with bioslurry.

Table 31: Effect of biogas slurry with and without mineral fertilizer on sunflower yield

Treatment Computed yield: kg/ha % Increase over control

Control 1773.33 -
N @ 120 kg/ha 3233.33 82.33
Slurry @ 5 t/ha 2426.67 36.84
Slurry @ 10 t/ha 2206.67 25.00
Slurry @ 1 5 t/ha 2573.33 45.11
Slurry @ 5 t/ha + N@ 60 kg/ha 2706.67 52.63
Slurry @ 10 t/ha +N @ 60 kg/ha 2226.57 25.55
Slurry @ 1 5 t/ha + N @ 60 kg/ha 2646.67 49.24
Source: Adapted from Clarita et al., 1982, cited in Dhussa, 1986:115

In sunflower, the use of biogas slurry alone in various doses and the combination of the same doses with
N @ 60kg/ha gave lower yields than the treatment with N @ 120 kg/ha. However, even the lowest dose
of (5 t/ha) gave yield that is 36.84% higher than the control. If the potential of biogas slurry as
organic manure is noted at this point (Dhussa,!985:26), it should also be noted that farmers would
probably put other organic manures in their sunflower field. In that case, it is illogical to attribute
superiority in the absence of comparison with other organic sources.

Tentscher (1986) reports the result of one of the studies in slurry utilization in crop production in
Thailand in which digested pig manure was compared with chemical fertiliser for the yield performance
of vegetable, maize, mungbean and morning glory. The diluted pig manure contained about 0.4%

27
and 0.04% total nitrogen. Effluent was applied as top dressing throughout the growth. The
amount of nitrogen supplied through the effluent was 50%, 100%, and 200% of nitrogen in
chemical fertiliser. Chemical fertiliser was applied at the rate of 124-52-124 kg/ha for vegetable corn,
mungbeans, and morning glory respectively. The treatment supplying 100% N in effluent gave
significantly better performance and was at par with chemical fertiliser. For mungbeans, increasing
application did not increase the yield significantly--a finding which was also reported by Dhussa (1985)
in India {reviewed earlier), though experimental design and treatments varied in these two studies. The
yield performance of the treatment with 50% N was as good as chemical fertilizer. In the case of
morning glory, plant height increased significantly with the treatment involving the supply of 100%
and 200% N, but it was significantly more so at 200% N ( at par with chemical fertiliser).

Koglevi (1987) reports on an agronomical field trial at the Centre National Agro-pedologie in the
west African nation of Benin. The purpose of the trial was to study the influence of bio digester
effluent on tomato, capsicum, lettuce and cauliflower. Table 30 below presents data from this trial.
Table 32: Average yield (t/ha) of vegetables with mineral fertilizer and
effluent application

Treatments Tomato Capsicum Lettuce Cauliflower

Control 2 4 26 23
Mineral Fertilizer 13 6 56 36
Effluent @5 t/ha of 22 12 130 48
Source: Kogtevi, 1987:1
The table above shows the superior manurial value of bio digester effluent over control as well as the
treatment involving chemical fertiliser.

In an experiment carried out in Peru (Vargas, 1986) during 1983-85 with biol (liquid portion of
biogas slurry) and biosol (solid sludge) on alfalfa and maize, it was found that biol as well as
increased yield in these crops by more than 25%.

Studies conducted by Sukhadia University of Udaipur, India (1986 Annual Report, Cited by Gupta,
1991:24) reported the following changes in N.P.K levels in soil after slurry application.

Table 33: Changes In soil NPK levels after slurry application

NPK at various depths (%)

N P K
Before Slurry Application 0.I32-0.I38 0.145-0.166 0.870-0.885
After Slurry Application 0.156-0.236 0.145-0.190 0.870-0.880
Source, Gupta, 1991: 25

Both N and P content of the soil increased after slurry application. The same university also
compared the effect of various fertilisers on the yield of cabbage, mustard and potato.

28
Table 34: Effects of various fertiliser combinations on the yields of cabbage, mustard, and
potato
Percentage increase
Treatment Cabbage Mustard Potato
1. Control ----- ----- -----
2. Farmyard Manure 18.67 25.80 25.33
3. Slurry 20.63 45.75 34.75
4. Slurry + Single Super phosphate 20.70 49.75 -----
5. Slurry + Rock Phosphate 15.9 35.25 -----
6. Slurry + Potash 24.9 ----- -----
7. FYM + Phosphate ----- 33.98 -----

Source: Gupta, 1991:25

Gupta (1991:25-26) also reports the results of 15 demonstrations launched during the Khariff, 1988
under the National Project on Biogas Demonstration through Foundation for Rural Recovery and
Development. Table 35 below presents data from these demonstrations.

Table 35: Effect of slurry on the yield of different crops in India (Khariff, 1988)
Crop No. of demonstration % increase in yield over control plot
Rice 8 28.87 (Average)
Tomato 2 70.5 (Average)
Chillies 1 0
Brinjal 1 74.00
Bajr3 1 33.00
Maize 2 56.75 (Average)
Cabbage 1 20.00
Potato 1 34.74
Urad I 67.00
Groundnut 1 25.00
Source: Adapted from Gupta, 1991:26 40.98
Overall percentage increase in yield from crops treated with biogas slurry came around 40%. The
application of biogas slurry manure gave best results in vegetable crops such as tomato and brinjal
followed by crops like maize and urad. Percentage increases in crops like bajra, rice, groundnuts
were modest. In case of chillies, there was no increase at all.
According to Singh (1990: 125), the increase in yields was considered substantial for, practically,
there was no extra cost for the fertilizer material used. Among the eight Indian states in which
these l demonstrations' were conducted, the response was better in dry areas with low soil fertility
levels and in which doses of inorganic fertilizer used were low. These states included Andhra
Pradesh, Madhya Pradesh, Orissa, and South Bihar.
The responses were moderate in irrigated wet areas with higher doses of fertilizer application
such as in the Punjab, Madhya Pradesh, Haryana and North Bihar. Singh (1990:125) and Gupta
(1991:26) note that those conclusions are based on scanty data and should not be considered
as conclusive. The inferences to be drawn are not to be considered as conclusive but as
indicative of an hypothesis for detailed experimentation and further scrutiny by the scientific
community (Singh, 1990 :125).
On the other hand Singh (1991:1-2 and personal communication) also notes that biogas slurry
manure demonstration cannot be a very scientific agronomic experiment; these are, and ought to
be, simple on- farm farmer participatory trials in which farmers can see for themselves an assess
the performance in yields.

29
During the Rabi season of 1988-89, one hundred slurry demonstrations were conducted in ten
Indian states, namely, Andhra Pradesh, Bihar, Haryana, Kerala, Madhya Pradesh, Maharastra,
Orissa, Punjab, Tamil Nadu , and Uttar Pradesh (Singh, 1990: 125). Of these the results of 82
demonstration are presented in the following table (the results of the remaining eighteen
demonstrations were either not received or discarded for various reasons).

Table 36: Effect of biogas slurry on crop yield in the Indian States (Rabi, 1988-89)
Crop T.N., A.P., Orissa M.P MR Bihar Punj & U.P Total
Kerala Haryana
CN (2)22% -- -- -- -- -- -- (2)22%
Maize -- -- -- -- (1)16% - - (1)16%
Millets (1)100% {1 )42% (1)14% -- -- ~ (1)6.5 {4)40%
POL -- (2)19% -- -- -- -- - (2) 19%
PUL (4)11% ~ (1 )20% -- -- -- -- (5)15%
Rice (6)43% -- -- -- -- -- - (6)43%
VEC (2)30% -- -- -- -- -- -- (2)30%
WHT — — (6)20% -- {19)21% (10)21% {25)22% (60)21%
(15) (3) (S) -- (20) (10) (26) (82)
GN-Groundnut; PUL -- Pulses; V EG -- Vegetable; WHT -- Wheat; TN -- Tamif Nadu; Pot.-- Potato
A.P. -- Andhra Pradesh; M.-- Madhya Pradesh; U.P.--Uttar Pradesh; Punj.-- Punfab
Figures in parentheses indicate the number of demonstrations. % indicate the percent
yield increase in demonstration plot over control plot. Millet includes jawar, ragi,
and oats. Pulses include blackgram and green gram Source: Singh (1990:126)

The average works out to be 23.6% (the table is not clear about how this figure can be arrived at,
because a simple averaging gives a couple of percentage points above this figure). Nonetheless, it
can be seen that the average incremental yield in Rabi crops is modest as compared to the earlier
report of Kharif crops (40%). Singh argues that since Rabi crops in most places are cultivated in
irrigated and relatively more fertile lands, the response is less impressive compared to Kharif crops.
It is still a substantive increment (Singh, 1990:127)

Biogas slurry also substantially invigorates plant growth in terms of root and shoot growth and the
general bulkiness of its vegetative parts. Gupta (1991:24) provides the following comparative data
on the effect of different types of manures and fertiliziers on growth of manures and fertilisers on
growth of tomatoes and chillies.

Table 37: Effect of different types of manures and fertilisers on the growth of tomatoes
Age of
plants (days) Root length Shoot length (cm.) Dry plants wt. (mg.)
control SDS FYM CF control SDS FYM CF control SDS FYM CF
10 2.8 5.8 4.5 3.9 7.4 11.2 9.8 8.2 29 183 48 36
20 3.2 6.2 5.5 10.3 8.6 13.4 12.2 10.3 42 262 107 48
30 4.1 7.8 7.2 11.2 9.3 16.2 14.2 i.2 50 506 195 105
40 4.8 9.2 8.6 12.5 10.2 17.8 16.5 12.5 58 912 357 182
SDS- Sun-dried slurry; FYM- Farm yard manure; CY- Chemical fertilizer
Source: Gupta (1991:24)

Except on the root length (from 20 to 40 days in which chemical fertiliser bettered), SDS showed
better performance, in shoot growth and plant weight (dry) than control, FYM, and chemical
fertiliser in all the growth stages (in terms of the given number of days).

30
Table 38: Effect of different types of manures and fertilisers on growth of chillies

Age of plants Root length Shoot length (cm.) Dry plants WL Inc.)
(days) control SDS FYM CF control SDS FYM CF control SDS FYM CF
10 5.3 7.6 7.1 6.2 8.9 12.6 11.8 10.2 40 130 53 48
20 6.1 7.8 7.8 7.1 9.6 14.2 12.6 11.8 56 340 107 52
30 6,9 10.8 8.2 7.8 10.3 15.3 15.5 12.6 66 462 134 98
40 7.5 12.6 7.8 8.0 11.2 16.9 17.0 13.8 72 868 213 252
SDS- Sun-dried slurry; FYM-Farm yard manure; CF-Chemkal fertilizer
Source: Gupta (1991:24)

Despite some of the experimental results reviewed earlier, SDS out performed control, FYM and
chemical fertiliser in all the three categories of plant growth (root length, shoot length and dry plant
weight) in all the four growth stages (number of days).

In India, from the mid-1980s, the Ministry of Non-Conventional Energy Sources (MNES) launched
a country wide "demonstration" programme in farmers field through state agencies, Gujrat State
Fertiliser Co-operative (GSFCI, India Farmer's Fertiliser Co-operative (IFFCO), Regional Biogas
Development and Training Centres and Voluntary Organisations like FORRAD (Tripathi, 1993:11).
By 1991, over 3000 slurry demonstrations' were conducted all over India.

Two plots of equal size were shown with the same crop. Biogas slurry was applied in only one plot
("demonstration" plot) at the rate of 10 tones per hectare in irrigated and 5 tones per hectare in non-
irrigated areas. Both plots were given uniform packages of other agronomic practices i.e. fertiliser,
seed rate, irrigation, pesticides etc. On maturity, crops from both the plots were harvested and yields
compared. Table 39 below provides a summary of results of the demonstrations conducted between
1984-85 to 1991-91 by state agencies from the Indian states of Haryana, Himanlchal Pradesh, Kerala
Karnataka, Madhya Pradesh, Gujrat, Goa, Punjab, Uttar Pradesh and Tamil Nadu. These states by
themselves represent a number of agro-climatic zones and soil type. By 1991, over 3000 slurry
demonstration were conducted all over India at the initiative of the Ministry.

Table 39: Summary of results of slurry1 demonstrations conducted by concerned state

departments/agencies in India (1984-85 to 1990-91)
Crop No. of demonstration Over ail average of % increase in crop
yield in slurry treated plot over untreated
plot
Paddy 88 31.95
Wheat 127 24.69
Maize 14 40.46
Millet 4 40.46
Turmeric 1 27.05
Potato 5 30.85
Chillies 2 24.25
Tomato 3 126.10
Groundnut 8 23.99
Banana 3 4.69
Brinjal 4 103.23
Sugar cane 2 6.29
1
The two major reports (Singh, 1991:1-8 and Tripathi, 1993:11-14) from which this table was compiled do not indicate the
form of biogas slurry (fresh slurry, slurry compost, sun-dried slurry) used in these demonstrations. Singh (1993:12) does
not mention it in his 'materials and unshod' portion of the report. In the concluding part he has mentioned that "As far as
possible wet slurry should be utilized to in the field to avoid loss of ammonia". It seems rather a suggestion and it still is
not clear as to what form/s of biogas slurry were used m these demonstrations.

31
Mulberry 1 25.00
Pulses 5 15.00
Mung I 10.40
Bajra 4 35.10
Lady's Finger ! 66.60
Mustard 2 23.00
Jute 1 50.00
Deccanhemp 1 50.00
Tapiaco 1 10.40
Ragi 8 27.00
]awary J 8.30
Urad 2 34.20
Pea 14 60.18
Total 252 35.94
Source: Singh, 1991:8; Tripathi, 1993:13

The demonstration areas represent various agro-climatic zones, and variations in percentage increase
in these zones can be seen as obvious. Even if Singh concludes (Singh, 1991:2) that the overall
percentage increase in yield due to slurry application is around 30% the above table gives the figure
around 36%. Singh argues that this result alone justifies the acceleration of National Project for
Biogas Development in India.

The Gujrat State Fertiliser Corporation (GSFC) also conducted demonstrations on a variety crops
during 1989-90. Table 40 below provides a summary of results of these demonstrations.

Table 40: Summary of results of demonstrations on the effect of biogas slurry* on crop production
(GSFC, India, 1989-90)
Crop No. of demonstration Over all average of % increase in
crop yield in slurry treated plot over
untreated plot
Paddy 4 10
Maize 4 18
Wheat 51 15
Groundnut 7 18
Jawar 2 21
Bajra 8 15
Gram 3 15
Mustard 3 11
Tobacco 2 13
Castor 1 3
Cotton 4 18
Green Gram 3 22

Total 92 14.91
Source: Tripathi, 1993: 13 * The summary report does not state the form of slurry used

Overall percentage increment in all these demonstrations can be seen as widely fluctuating. This
has to be so because of the variations in agro-climates, nature of feed stock, types of animal
feeds, slurry storage and handling, etc. Nonetheless, yield increments are reported in most of
the crops in which demonstrations were conducted.

The large scale demonstration program conducted by FORRAD, GSFC, and state
agencies/departments throughout India showed an overall average increase of 24.2 percent on a
national basis. Except for some, most of the cases have shown good incremental yield.

32
In addition to increased crop yield, some of the positive observations made during the field
demonstrations are summarised as follows:

• Improvement in quality of produce. For example, the size of vegetables like cabbage,
• tomato, potato, Brinjal, etc. were significantly increased
• Reduction of weed in biogas slurry plots
• Biogas slurry does not attract insert breeding
• Reduces the usage of chemical fertilisers. This indirectly helps in reduction in unit cost
• of produce.
• Biogas slurry has high water holding capacity which helps rainfed crops
• Seeds treated with biogas slurry have better germination rate
• Biogas slurry contains larger amount of organic matter and free ammonia than available
• in compost manure, but free ammonia is lost if slurry is dried in the sun
• Biogas slurry is ready for use in the shortest possible time
• If nightsoil and cattle urine is added, N and P2OS availability in biogas slurry is
• strengthened (Tripathi, 1993:14)

As in many other recommendation (See also Kijne, 1984:105 inter alia), Tripathi also concludes that
as far as possible wet slurry should be utilised in the field to avoid loss of ammonia. However it
should be noted that fertilisation directly following digestion will hardly take place since fertilisation
of crops is tied to special application periods {Kijne, 1984:7; Demont et al., 1990:12). Thus storage
of wet slurry is an important issue and will be covered separately. Furthermore, research into the
'yield depressing effect' of fresh slurry (Acharya, 1961; Maskey, 1978 inter alia) due to excessive
nutrient supply (Arnott, 1986; Sathianathan, 1975 inter alia), or due to H2S and other toxic effects, is
far from being conclusive. If these experiments have revealed the yield depressing effects of fresh
wet slurry, time and again the application of the same is recommended. Thus, the effects of various
concentrations of wet slurry along with toxic effects, the nature of feedstock, etc., needs further
research.

Singh et al. (1995:4-1) report on another series of experiments on the effects of biogas slurry on crop
production which were conducted under the aegis of the Renewable Energy Sources Research and
Development Programme of Che All India Co-ordinated Research Project (AlCRP) on Renewable
Energy Source for Agriculture and Agro-based industries. Twelve research Centres spread over in
different agro-climatic regions of India participated in this relatively long term R and D activities.
Table 41 presents data on optimum level of slurry application in various crops along with yield.

Table 41: Summary of the evaluation of manurial value of biodigested slurry for various cereals and
other crops in different agro-climatic zones in India
s. Agrocli Soil Crop Variety Optimum level of Year Grain Yield Centre/
N. made Type N substitution (q/ha) Institution
region through slurry
(%)
Opt Control
treatment (SO F100)*
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10}
1. 1 Red Potato Kufti Jyoti 100 1992 279.0 235.0 HPAU,
Loam Palampur
2. II Sandy Wheat Sonalika 25 1990 31.3 24.4 AAUr Jortiat
Loam
Maize NLD 50 1992 At par 100 with Urea AAU, Jortiat
Composite %N
Paddy Mansuri 75 1989 25 24.3
IR-50 1990 21.3 21.7
Culture-I 1989 9.1 11.6
3. VI Sandy Wheat HD-2329 50 1990 47.0 46.3 IARI, New
loam Delhi
1991 24.1 24.4
Sandy Wheat HD-2329 50 1990 54.9 65.6 PAU,
loam ludhiana
Sandy Wheat Sonalika 50 1989 25.5 25.4
loam

33
 Fine -dto- -dto- 25 over and above 1992 26.9 25.4 IAR!, New
loamy 100% N thro' urea Delhi

50 1992 28.3 25.4

-dto-
Sandy Maize Ganga-5 40 1986 44.88 43.8
loam
1987 28.6 29.6
Sandy Paddy PR-106 40 1987 90.4 74.8 PAU,
loam Ludhiana
4. VllI Clay Wheat Sonalika 75 1988 50.1 45.8 CEAE, Bhopal
(Vertisols)

1980 43.1 40.3

1990 40.1 39.6
Soybean Durga 75 1988 1.5 23.3
1989 18.8 M
1990 18.4 15.8
Sandy Wheat MACS-9 1988 35.6 36 RAJAU,
loam Udaipur
Mustard 60 1988 22.9 22.5
5. IX Medium Wheat MACS-9 60 1984 14 14.2
black
6. X Clay Maize Ganga-5 50* 1986 50.2 51.7 TNAU,
loam Coimbatore
Regi OH 50 1086 32.5 31.7
Slack Sorghum Hybrid 50 1987 59.4 52.8 UAS,
soil Dharwad
CSH-5 1988 31.3 34.4
Maize Ganga-5 50 1989 21.7 21.8
Chilly Bydagi 25 1991 53.2 36.2
1992 34.4 39.4
1993 28.6 25.5
50 + 1993 40.4 25.5
Azospirillum
culture ICM 1001
(Biofertilizer)
7. XI Sandy Paddy Moti 60 1990 47.5 48.7 CRRI, Cuttack
loam
8. XII Red CN 50 1989 25.1 26.6 SPCW,
loam Courtallam
Brinjal MDU-I 50 1992 23.8 21
Source: Singh et al., 1 995:14 *Slurry=O: Chemical fertilizer = 100kg/ha
GN : Groundnut
AAU: Assam Agricultural University
CIE: Central Institute of Agricultural Engineering
HPAU: Himanchal Praddesh AgriculturaJ University
IARI: Indian Agricultural Research Institute
PAU: Punjab Agricultural University
R.AJAU: Rajasthan Agricultural University
TNAU: Tamil Nadu Agricultural University
UAS: University of Agricultural Science, Dharwad, Kamataka

The grain yield data showed that 50 percent of nitrogen requirement of wheat crop (HD-2329,
Sonalika and MACS-9) could be met through slurry application in sandy loam soil of agro-

34
climatic region-VI and medium black soil of region IX (Delhi, Ludhiana, Pune) respectively without
affecting grain yield significantly. The same level of nitrogen substitution through slurry also
showed for maize (Ganga-5 and NLD Composite), ragi (Co-11) and sorghum (Hybrid CSH-5) in
clay loamy/black soils of region X and groundnut crop in red soil of region XII (Coimbator,
Dharwad and Courtallum). Additional dose of nitrogen through chemical fertiliser resulted in
slightly higher grain yield of wheat (Sonalika) under fine loam soil of region VI (New Delhi): Root
density showed marked increase with the addition of slurry through chemical fertiliser as compared
to control. Around 75 percent of nitrogen need of wheat (Sonalika) and soybean (Durga) was met
through slurry in clay (vertisols) soils in region VIII (Bhopal), no significant reduction in grain yield
was observed. The same level of nitrogen substitution was found for paddy crop (Mausuri, R-50,
Culture-1) in region II (Jorhat, Assam). Biogas slurry met 60 percent needs of wheat, mustard and
paddy (Moti) in Udaipur and Cuttack. Around 40 percent nitrogen substitution through slurry
application was found to be optimum for maize (Ganga-5) and paddy (PR-106) in sandy loam soil of
New Delhi and Ludhiana. Slurry could, however, meet only 25 percent of nitrogen needs of wheat
(Sonalika) and Chilli (Byadagi) In sandy loam soil of Jorhat, Assam and black soil of Dharwad,
Karnataka respectively. Addition of azospiriilum culture (ICM100I) at 50 percent slurry substitution
in chilli (Byagdi) in black soil of Dharwad, Karnatak improved yield level by 58 percent. Biogas
slurry was able to meet complete nutrient requirement of potato crop (Khufri Jyoti) in Palampur,
Himanchal Pradesh.

Although reviews of research in the application of biogas slurry in seed treatment will be taken up
separately, it is pertinent here to note that this series of experiments also included seed treatment
with biogas slurry. Soaking of wheat seeds (HG 2380) for 6-12 hours in slurry and water before
sowing resulted in significant increase in germination percentage at Palampur, Himanchal Pradesh.
In addition, mean germination time is reduced and the root length of seedlings increased. In
Dharwad Karnataka, application of slurry stimulated beneficial microbiological activities in respect
to fungi, phosphorous solublizer and nitrogen fixing azotobactor (Singh, et al., 1995:15)

Kanthaswamy (1993) reports the result of studies on effect of biogas slurry on rice carried out in
farmer's field in a village in Kanyakumari in South India. The soil was wet, black loamy and the rice
variety used was TPS I. Table 42 below presents data on grain and straw yield for the different
treatments followed.

Table 42: Effect of biogas slurry on rice grain and straw yield in South India
Treatments Grain Yield % Increase Straw Yield % Increase
kg/ha over control kg/ha over control
T1— Control 3546.06 _ 6070.29 -
T2-FYM 12.5 t/ha 4304.84 21.37 5298.85 -12.70
T3-BGDS 5 t/ha 4368.07 23.18 5109.16 -15.83
T4—BGDS 10 t/ha 4722.1 7 33.16 5298.85 -12.70
T5-BGDS 15 t/ha 5316.56 49.92 5551.78 -8.54
T6-BGDS 10 t/ha+ 25% NPK 4873.93 37.43 5172.39 -14.79
T7—BGDS 10 t/ha+50% NPK 4810.70 35.66 6500.26 7.08
T8—BGDS 1Ot/ha+75%NPK 5000.40 41.01 7195.82 18.54
T9-BGDS 10 t/ha+ 100% NPK 4809.44 35.62 7828.14 28.95
T10-FYM 12.5 t/ha + 25% NPK 4808.17 35.59 5425.32 -10.60
T1 1-FYM 12.5 t/ha+50%NPK 4241.61 19.61 5045.92 -16.87
T12-FYM 12.5 t/ha+75% NPK 4873.93 37.44 5678.25 -6.45
T13-FYM 12.5 t/ha+ 100% NPK 4431.31 24.96 6247.34 2.91
T14-NPK 100% 4115.15 16.04 6120.87 0.83
FYM-Farmyard Manure; BGDS-Biogas Digested Slurry
Source: Adapted from Kanthaswamy, 1993:46

Interestingly, application of BGDS alone at T5 (15t/ ha) recorded maximum yield (5316.56 kg/ha)
and it was at par with T12 (FYM I2.5t/ha +75%NPK--4873.93 kg/ha), T8 (BGDS10t/ha-h 75%

35
NPK--5000.4 kg/ha), and T6 (BGDS 10t/ha +25% NPK--4873.93 kg/ha). The control recorded the
minimum yield (3446.06 kg/ha). The results have also shown that the application of BGDS in
combination with fertilizers like urea, superphosphate and muriate of potash give higher grain yield
than when these fertilizers were applied alone. On the whole, these data on rice production showed
that the application of BGDS significantly influenced the grain yield and that the highest grain yield
was obtained by applying BGDS @ 15t/ha.

The earlier studies by Laura and Idnani (1972), Sankaran et al.r(1981) and Sankaran and
Swaminathan (1988) reported the same trend in grain yield in their respective experimental crops
(Kanthaswamy, 1993:46)

Maximum straw yield was recorded in T9 (BGDS 10 t/ha +100% NPK--7828.14 kg/ha) followed by
T8 (10 t/ha + 75% NPK--5045.92 kg/ha). This showed the effective combination of inorganic
fertilizer and BGDS in straw yield. Sankaran and Swaminathan( 1988) also reported the same trend
in Maize (Kanthaswamy, 1993:47).

Keyun et al. (1990:25) reports a successful case of biogas slurry utilization from Dongxu village,
Jinagsu Province in China. According to the report, biogas fertilizer was applied to 106 hectares of
fertile fields for six successive years. Soil organic matter content raised to 2.7% in 1988 from 1.3%
in 1982. The grain yield doubled. Compared to the year 1982 the amount of chemical fertilizer
application dropped by 86% The report, however, does not mention the amount and form of
bioslurry used) . The net income per hectare was reportedly four times higher than in the
neighbouring villages that did not use biogas fertilisers.

For China as a whole, Karki et al.( 1995:2) report the 'average growth rate' of various crops and
vegetables2 as given in the following table.

Table 43: Effect of biogas slurry in crop yield in China

Crops Incremental Yield {%)
Wheat + 13.60
Com + 16.90
Rice + 9.40
Rape seed + 1.90
Cotton + 20.20
Sweet potatoes + 18.80
Vegetables + 25.00
Source: Karki et al., 1 995:2

On an average 10-20% increase in yield has been reported for China.

The APRBRTC (1983) reports the results of field experiments conducted in 16 counties in Sichuan
province of China. The experiment involved comparison of effects on crop yield of digester effluent
and open air pool manure. Table 44 below presents the summary of results.

2
The meaning of the expression 'average growth rate' is not clear, for in technical usage, growth rate
express temporal dimensions, and the report does not mention the year for which the average growth'
rate was calculated. If the report meant average annual incremental yield due to slurry application,
the mention of the year would have been helpful. No source is cited for further clarification

36
Table 44: Comparative effects of digester effluent and open air pool manure on crop yield

Crops Yield (jin/mu) Increase Number of

D.E Check jin* / mu** % Tests
Rice 634.4 597.5 38.9 6.5 18
Maize 555.9 510.4 45.5 8.9 9
Wheat 450.0 390.5 59.5 15.2 29
Cotton 154.5 133.5 21.5 15.7 2
Rape 258.4 233.6 21.8 106 15
Source: APRBRTC, 1983: 156 D.E. Digester effluent
* I jin equals 1/2 kg
** I mu equals 0.667 ha.

The above table shows an average incremental yield of 14.6%. Based on these data it has been
concluded that "the digester effluent is better than open air pool manure regardless of the kinds of
soils and crops" (APRBRTC, 1983:156).

Air dried digester sludge is also reported to have increased soil fertility and crop yield in China.
Table 45 below presents data on this respect.

Table 45: Effect of digester sludge on crop yield in China

Crops Amount of D.S. applied Yield {jin*/mu**) Number of tests
(jin/mu) D.S. Check jin/mu %
Sweet potato 2250 3236.0 2863.0 373.0 13.0
Rice 2000 871.9 798.9 73.0 9.1
Maize 3000 667.5 617.7 49.8 8.3
Cotton 3000 166.6 154.3 12.3 7.9
D.S-Digested sludge
I jin equals 0.5 kg
I mu equals 0.667 ha.
Source: APRBRTC, 1 983:1 56

The air-dried digested sludge on the average increased yield by approximately 10% over the control
as compared to about 15% in the case of digested effluent.
The application of digester effluent in combination with ammonium bicarbonate [ (NH4)HCO3] has
increased crop yield and soil structure that are deteriorated as a result of continuos use of large doses
of fertilizer in China. Table 46 presents data on the increased crop yield by the application of such a
combination.
Table 46: Effect of digester effluent + (NH4) HCO3 on the yield of rice and maize in China
Treatment Rice Maize
Yield Increase Yield Increase
(jin/mu) (jin/mu)
jin/mu jin/mu %
Check 696.7 - - 566.7 - --
Digester effluent @4500 jin/mu 736.6 39.9 5.7 677.3 106.0 18.8
(NH4)HCO3@20iin/mu 736.0 39.9 5.7 620.2 53.3 9.4
Effluent @ 4500 jin/mu + 781.3 84.6 12.1 780.0 213.3 37.6
(NH4)HCO3@? jin/mu
Source: 1 jin equals 0.5 kg
1 mu equals 0.667 ha.
Source: APRBRTC, 1983:158

37
As the table shows, the combination of chemical fertilizer and digester effluent substantially
increased the yield of both rice and maize.

Based upon the analysis of these results and depending upon the crops, soil types and agro-climates
25-100 percent replacement of chemical fertilizers with bioslurry has been recommended in India.

Singh et al. (1995) reports the results of study on the effea of biodigested slurry for raising pea
(Pisum sativum L), okra Abelmaschest esculentus L.), soybean (Glycine max L.) and maize (Zea
mays L.) in the hilly condition of Kangra district in Himanchal Pradesh (Alt: 5O0-5500m arnsl).The
experiments were conducted in the areas located between 900 to 1300 m amsl with four treatments
and five replications.

Table 47: Details of the study pertaining to comparative effect of different fertlizers on pea, okra,
soybean, and maize in Himalchal Pradesh, India
S.N. Crop Variety Soil Area (m2) Treatment
1 Pea Linkon Sandy 500 T,= Farmers practice (10 FYM and 19.32 kg
Loam N/ha) T2 * Recommended dose of fertilizer
{10 TFYM, 25 T3 = iO T biogas digested
slurry, 25 kg N, 60 kg P and K/ha T4 =12.5 T
Biogas digested slurry, 60 kg P and K/ha

2 Okra Pusa Silty Loam 360 T,= Farmers practice (6 FYM and 48 kg
Sawani N/ha) T2 = Recommended dose of fertilizer
(10 TFYM, 72 kg.N, 50 kg P and K/ha) Tj =
5 T biogas digested slurry, 72 kg N, 50 kg P
and K/ha T4 = 12 T Biogas digested slurry, 50
kg P and K/ha

Soybean Shivalik Silty Loam 1000 T,= Farmers practice (10 FYM and 16.25 kg
N/ha) T2 = Recommended dose of fertilizer
(20 TFYM, 20 kg. N, 60 kg P and 40 kg K/ha)
T3 = 10 T biogas digested slurry, 25 kg N, 60
kg P and 40 kg K/ha T4 = 12 T Biogas
digested slurry, 60 kg P and 40 kg K/ha

4 Maize Himvijaya Sandy 1400 T,= Farmers practice (10 FYM and 70 kg
Loam N/ha) T2= Recommended dose of fertilizer
(10 TFYM, 25 T3 = 10 T biogas digested
slurry, 25 kg N, 60 kg P and K/ha T4 = 12.5 T
Biogas digested slurry, 60 kg P and K/ha

Source: Singh et al., 1995:5

The doses of NPK were applied according to the recommended packages of practices for the
respective crops. The crop yields were analyzed for critical difference (CD) at 5 percent level.
Table 48 presents data on yield pod/cob size and plant height.

38
 Table 48: Effect of biogas slurry on pod/cob size, plant height and
yield of pea, okra, soybean and maize
S.N Crop Treatment Average length of Average plant Yield (q/ha)
pod/cob (cm) height (cm)
1 Pea T1 8.58 73.10 88.60
T2 8.83 74.85 105.6
T3 9.25 76.92 125.6
T4 8.10 72.26 76.80
CD. (5%) ---- ---- 12.68
2 Okru T1 8.68 73.34 105.78
T2 9.45 75.13 114.54
T3 11.27 78.81 130.10
T4 8.36 72.56 96.74
CD. (5%) ---- ---- 8.03
3 Soybean T1 4.15 88.43 22.00
T2 4.50 96.26 26.00
T3 5.00 98.43 29.60
T4 4.10 68.03 20.40
CD. (5%) ---- ---r- 3.70
4 Maize T1 18.14 160.58 19.10
T2 19.86 165.12 22.42
T3 21.46 176.51 1 29.17
T4 18.05 59.54 18.80
CD. (5%) ---- ---- 2.45

Source: Singh et al., 1995:5

As the table shows, all the crops under consideration gave highest yield in the treatment, T3 where
balanced amount of biogas slurry was used with chemical fertilizers, T, (farmers' traditional dose) is
deficient in organic and inorganic fertilisers, T4 has complete NPK dose but release of nitrogen is
slow at critical growth period because the major portion of N was supplied through biogas digested
slurry - the reasons for low yield in T,, and T4. In case of maize, okra and soybean, the yields under
T, was at par with T4j but in pea, the yields were significantly higher at T, and T4. In all the crops
under trial, balanced fertilizer dose with FYM (T2 and balanced dose with biogas digested slurry (T3)
gave significantly higher yield than T,
in all the crops, the yield corresponded with plant height and length of pods/cobs. The total nitrogen
dose in T4 was in the form of biogas digested slurry. In this form total amount of nitrogen was
probably not available to the crops at critical stages due to its slow rate of release. The next crop
might have received the residual effect; to look into this aspect was not the purpose of this
experiment.
The report concluded that biogas slurry is a better organic manure than farmyard manure for
obtaining higher yield in pea, okra, soybean and maize. In comparison to the farmyard manure,
biogas slurry if used along with recommended dose of chemical fertiliser, can give better crop
production. Thus biogas slurry was concluded to be a superior manure for raising crops than farm
yard manure (Singh, 1995:7).
Kologi (1993: 20-22) reports the results of the experiments on the effects of biogas slurry conducted
in different locations in North Karnataka. Experiment and check plots of equal (one acre each) size
from fairly uniform soils (red, medium black and black soils) were laid out. The scheme for the
experiment was as follows:
Treatment (T): Application of biogas slurry @ 10 t/ha three weeks before sowing along with
recommended dose of fertilizer.
Check (C): Application of recommended dose of fertiliser only.

39
The data are presented in Table 49 below.
Table 49 : Comparative effects of chemical fertilizer and biogas slurry + chemical fertilizer
on various crops, North Karnataka, India
Crop Variety Year of expt Yield {kg/ha) % increase
Expt. plot Check
Groudnut Dh-8 1985 3000 2250 33.34
Groudnut TMV-2 1988 2500 2000 20.00
Sunflower Morden 1987 1000 875 14.20
Sunflower BSH-1 1991 1650 1375 20.00
Sunflower A-1 1987 750 600 25.00
Cowpea C-152 1987 875 687.5 4.50
Cowpea C-152 1988 300 250 20.00
Hy. Cotton DCH-32 1985 2375 2125 11.76
Hy. Cotton DCH-32 1988 2000 3 500 33.30
Hy. Cotton DCH-32 1987 2500 2000 25.00
Wheat HD-2189 1987 3000 2500 20.00
Wheat HD-2189 1991 1850 1300 42.31
Source: Kologi, I 993: 21
In Groundnut, the yield increased in the range of 20 to 33 percent (average: 26.27 percent) and the
pod number per plant ranged from 60 to 70 as compared to 45 to 55 in the control, Sunflower
showed an incremental yield of 25 percent. The plants from the treatment plot was1 also reported to
be healthier and taller than those from the control plots. Incremental yield in Hybrid cotton ranged
from 11.76 to 33.33 percent with an average increase of 23 to 35 percent. Cowpea showed an
incremental yield of 20-24.5 percent (average: 22.25 percent). In sunflower the increase in yield
ranged from 14.2 to 20 percent (average: 17 percent ). Better crop growth, better head size and
intense green colour of the plant was reported in the treatment plot.
On the whole incremental yield ranged from 1 1.76 to 42.31 percent for all the crops under trial. The
average increase of 24 percent is similar Co the national average of yield increment due to biogas
slurry as reported by Tripathi (1993:14). The highest increase in yield was observed in wheat and
groundnut, followed by sunflower. Kologi et al. (1993:22) note that yield increased due Co
application of biogas slurry irrespective of the types of soil in the trial plots.

Most studies have thus reported some combination of biogas slurry with chemical fertilizer to be
more effective over FYM and chemical fertilizer. A survey of farmers opinions and perception about
the use of biogas slurry in a village in Uttar Pradesh reported the following finding:

"With HYV seeds, productivity is in the order: slurry + chemical fertilizer> Heap Manure +
Chemical fertilizer (Santosh et al., 1993.37)"

Field investigations were carried out in two phases at Annamalai University experimental farm,
Annamalainagar, Tamil Nadu, India (Kuppuswami et al. 1993:15-19) to study the effect of slurry and
gypsum enriched biogas slurry on rice and succeeding blackgram (Vigna muneo). In the first phase,
the direct residual effects of plain gypsum enriched biogas slurry were compared with farmyard
manure. In the second phase plain gypsum enriched slurry along with three levels of NPK were
tested. Table 50 and 51 below present data from these experiments.

40
 Table 50: Direct and residual effect of bio-digested slurry on rice and blackgram
Rice Blackgram
Treatment details
Tiller Panicle Grain yield Straw Pod number plant Gram yield
number hill number t ha -1 yield -+ Kg ha -1
-1
m-2 t ha -1
Wet bio-digested slurry @ 6.83 384 7.46 13.03 9.21 422
10 t ha-1
Dried bio-digested slurry @ 7.08 385 7.80 13.69 8.94 383
10 t ha-1
Wet bio-digested slurry @ 7.58 413 8.41 15.25 9.12 402
10 t ha-1 with gypsum 50 kg ha-1
(1:0.025)
Farmyard manure @ 10 6.58 341 7.33 12.58 10.22 463
t ha-1
Farmyard manure @ 10 t ha ' 7.26 385 8.00 14.69 10.1 1 431
with gypsum 50 kg ha -1
(1:0.025)
Gypsum 50 kg ha-1 6.33 330 6.78 11.54 7.83 294
Control 6.17 324 6.61 1 1.03 7.70 292
CD (P=0.05) 0.22 0.06 0.19 0.49 1.24 51

Source: Kuppuswamy et al., 1993:16

Table 51: Effect of plain and enriched slurry on rice-blackgram cropping system

Treatment details Rice Blackgram

Tiller Panicle Grain yield Straw yield Pod number Gram yield
number hill number m-2 t ha -1 t ha -1 plant -1 kg
-1
ha-1
Control 8.36 332 3.2 5.60 22.33 586
IOO:50:5O:kgNPKha -1 10.37 363 4.56 7.20 32.68 988
Biogas slurry @ 10 tha-1 9.16 347 2.93 6.46 26.64 762
Biogas slurry + 100:50:50: 12.00 384 5.11 7.96 37.42 1 196
kg NPK ha -1
Biogas slurry 75:37.5:37.5 kg 1 1.66 381 5.06 7.76 36.86 1175
NPK ha-1
Biogas slurry + 50:25:25 kg 11.36 379 4.96 7.68 35.94 1170
NPK ha -1
Gypsum enriched biogas slurry + 13.63 408 6.14 8.85 42.92 1283
100:50:50:kg
NPK ha -1
Gypsum enriched biogas slurry + 13.94 411 6.23 9.05 43.68 1295
75:37.5:37.5 kg
NPK ha-1
Gypsum enriched biogas slurry 1.87 396 5.66 8.49 42.06 1279
+ 50:25:25kg
NPK ha -1
Gypsum enriched biogas slurry 9.56 350 4.03 6.68 228.16 787
@ 10 + ha-1
100:50:50kg NPKha1 + 500kg 10.48 361 4.53 7.16 32.91 1011
gypsum ha -1
CD (P=0.05 0.84 3.7 0.10 0.22 2.52 30.86

Source: Kuppuswamy, 1993:18

41
Table 50 above shows that biogas slurry at 10 t ha-1 enriched with gypsum 250 kg ha-1 gave an
additional grain yield of 1.80 t ha-1 compared to the control. Gypsum enriched biogas slurry had a
clear edge over slurry alone. The residual effect of FYM on the succeeding blackgram was
comparatively better than that of biogas slurry. Table 51 shows that gypsum enriched biogas slurry
in combination with 75% recommended NPK registered maximum grain yields in rice-blackgram
cropping system. Based on these findings it was concluded that the basal application of gypsum
enriched biogas slurry holds promise as a viable agronomic practice for the realization of higher
yields in rice-blackgram crop-sequence and the maintenance of soil fertility (Kuppuswamy etal.,
1993:19).

A field trial on a number of vegetable crops and wheat was conducted in AlEgarh in India for
studying the comparative efficiency of biogas slurry and chemical fertilizer Myles et al., 1993: 42-
44). The data are presented in Table 52 below.

Table 52: Effect of biogas slurry and chemical fertilizer on different vegetable crops

S.N. Crops Biogas slurry kg/plot Chemical fertilizer Control kg/plot

kg/plot
1 Tomato 196 230 140
2 Couliflower 528 492 350
3 Cabbage 177 154 120
4 Knol-khoi 859 785 615
5 Capsicum 23 25 !9
6 Peas 19 26 20
7 Gram 11 13 7
8 Onion 174 180 100
9 Wheat 74 85 55
Source: Myles et. al, 1993:44

Table 52 shows that in most cases biogas slurry is as effective as chemical fertilizer. In addition, it is
also reported that the quality of bioslurry applied vegetables were superior in quality. Myles et al.
have also worked out a comparative economics of biogas slurry and chemical fertilizer and claim
that ' biogas slurry use will out weigh the use of chemical fertilizer' {Myles et al. 1993:44)

From Columbia, South America, Campino (1990) reports the results of the effect of nitrogen from
liquid manure, bioslurry and urea on hay, and maize. The tests were conducted in a tropical climatic
environment in the region south of Cali at an altitude of approximately 800 meters in which the soil
was inceptisol (American classification) or pseudogley (German classification). The annual mean
temperature calculated per month was 24 degree centigrade, with only minimal monthly
fluctuations. Annual precipitation totaled around 1,700 mm. The tests on crops were begun in 1986.
An initial test with large allotments (6.0x0.0 m), which was not repeated, analyzed various organic
fertilizers. The object of the study was a three year old grass culture consisting of elephant grass
(Pennisetum puporeum) and king grass (Pennisetum hvbridm). The results indicated that liquid
manure and bioslurry brought the highest yields. Most importantly, nitrogen from these fertilizers
exhibited greatest effectiveness. However, the yields from these trials were lower in comparison to
those reported by Duclos (1975) and Pazold (1986) primarily because of the poor phosphorous
levels in the soil and irregular distribution of rainfall (Campino, 1990:19)

An Additional test (five repetitions) was conducted to see whether, in fact there were significant
differences between the effect of urea and increasing concentrations of liquid manure as well as
bioslurry. This test was conducted on a new elephant grass culture that was laid out not far from the
first one. The soil was clayey, acidic and deficient in phosphorous (2-3 ppm available to plants.
Around 20 ppm would be considered a good supply). Supplemental fertilization @ 75 kg/ha of P2O5
was applied.

42
This increasing concentration of liquid manure caused the yield to increase sharply. In contrast the
effectiveness of nitrogen decreased sharply as the N concentration increased. The comparison of the
three fertilizers also showed that N from urea was the least effective. Bioslurry performed slightly
lower than liquid manure.

Campino argues (1990:20) that the varying effectiveness of nitrogen from different fertilizers
depends upon the way it is converted in the soil. Three different routes may be taken by ammonia
which represents the first compound available to plants from the mineralization of urea or the
organic substance. The first route is absorption by plants and microorganisms in the soil; the second
is binding with clay minerals. The third route is nitrification. Although nitrification occurs relatively
slowly in acidic soils, it is an important aspect of nitrogen conversion in the soil. Nitrification is a
strictly aerobic process and hence takes place during drier periods. When there is rainfall
anaerobiosis occurs and denytrifying bacteria become active and nitrate is transformed into nitrogen
oxide, a process that results in considerable loss of gaseous nitrogen. Gerretsen and Hoop (1957) and
Focht (1978) inter alia have estimated that such losses could occur between 100 and 300 kg/ha N per
year (Campino, 1990:20-21).

Thus a decrease in the effectiveness of the nitrogen from the fertiliser with a high percentage of
ammonium or easily mineralizable compounds as in the care of urea is noted. The slight drop in the
effectiveness of the nitrogen from bio-slurry is attributed to the narrowing C:N ratio as a result of
anaerobic digestion.
The report is silent about what constitutes a ' liquid manure'. Test on Maize
This test involved the following treatments
1. Control (without fertilisation)
2. 75 kg/ha of urea (34.5 kg/ha N)
3. Liquid manure (75 m3/ha + 144 kg/ha N)
4. Bioslurry (1253/ha = 155 kg/ha N)

Monitoring of plant growth in terms of plant heights over a period of ten weeks served as the basis
for obtaining information about the availability of nitrogen.

It was observed that up to the third week not much differences occurred between the treatments
because of the lower nitrogen concentration in the urea treatment. In the first four weeks, bioslurry
treatment emerged as slightly superior to all other treatments. Finally, liquid slurry registered the
highest growth rate. If should be noted that once a moist period, the growth of the bioslurry
treatment decreased, although the nitrogen content in bioslurry was slightly higher than in liquid
manure, it is because the onset of rain fall creates anaerobic conditions in the soil, that along with the
high soil temperature promote denitrification with considerable nitrogen losses. Such loses are
directly proportional to the availability of nitrogen from the fertiliser (Campino, 1990:21). From
these experiments it is indicated that the effect of nitrogen from bioslurry lasts a maximum of six
weeks in warm and moist conditions This means that the effectiveness of a bioslurry concentration
depend substantially on the absorption rate of the crop in question at the time of application. In hay
crops, bioslurry concentration of 20 to 70 m3/ha are reported to be appropriate even if the
effectiveness of the nitrogen in higher concentration drops sharply in comparison to lower
concentration, observation that broadly correspond with the many slurry dose experiments
conducted in India reviewed earlier, and the observations from slurry fertilisation in Germany
(Schulz, 1990:7).

Jianmin et al. (1990:28-30) reports from China about an experiment involving the comparative
effects of slurry, chemical fertilizer and a combination of both. The mixture consisting of chemicals
and slurry produced the highest yield, but the best quality and best health of the plants were achieved
after using pure slurry.

43
In Egypt, Latif's (1990:275-279 ) research on bioslurry utilization involved, among others, the
evaluation of direct and residual effects of biogas manure as a complete substitute for NPK and
micronutrients on the yields of cotton, wheat, maize, broadbean, spinach and carrots. The application
of biogas manure at the rate equivalent to chemical fertiliser is reported to have resulted in increased
yield in these crops as presented in Table 53 below.

Table 53: Effect of biogas manure on crop yield in Egypt

Crops Yield Increase {%)
Cotton 27.50
Wheat 12.50
Rice 5.90
Broad bean 6.60
Spinach 20.60
Carrots 14.40
Maize 35.70
Source: Adopted from Latif, 1990:275-279

An average yield increase of 16.88 % can be discerned in these seven crops.

An experiment was conducted at the Central Luzon University in the Philippines on the effects of
manure (compost, night soil and pig-dung) and chemical fertilizer on string bean { Gaur et al, 1986:
108-109). As Table 54 below shows highest yield was obtained when the crop was manured with
nightsoil. The yield was further increased when the full dose of fertiliser was added.

Table 54 :Yield of string bean treated with different organic manures and chemical fertilizers

Treatment Yield (kg ) from a 3x5 m.

Compost Nightsoil Pig-dung
5 t/ha manure 2.37 3.13 1.93
5 t/ha manure + 3.95 4.33 4.09
60 + 80+100
5 t/ha manure + 3.63 3.77 3.44
30 + 40+50
10 t/ha manure 2.79 3.39 4.70
10 t/ha manure 3.65 3.84 3.53
+60+80+100
10 t/ha manure 2.77 3.86 3.46
+ 30 + 40+50

Source: Gaur el al, 1986: 108-109

This nightsoil and pig-dung used in the treatments were obviously not anaerobically digested. In
view of the nutrient preservation, relative increase of available nutrients, crop yield can be expected
to increase further after anaerobic digestion of night soil. And this is supported by other field
experiments in China involving anaerobically digested spent slurry from biogas plants based on
human excreta. These experiments have shown that use of spent slurry from anaerobic digestion of
human waste, pig waste and rice straw increased the yield of maize rice cotton and winter wheat by
28.1, 24.7 and 12.4 percentages respectively {Gaur et al., 1986).

44
3.2.2.1. Utilization of biogas slurry in seed treatment, insect control and foliar dressing

Seed treatment and disease-pest control is an important aspect of crop production. The review in the
following pages will cover some of the research works involving biogas slurry in this aspect of the
crop production enterprise.

Seed treatment is a technique of applying needed inputs such as organic, inorganic inputs,
biofertilizers and pesticides on the seed themselves in an effort to provide a self-sustaining seed unit
with an improved micro-environment for germination and seedling development (Lakshmanan et al,
1993:5). Seed coating provides an opportunity to package effective quantities of materials such that
they can influence the seed or soil in seed-soil interface (Scott, 1989 cited by Lakshmanan, et al.,
1993:5). As bioslurry contains soluble nutrients and numerous active substances like enzymes and
vitamins secreted by microbes which are capable of promoting metabolism of the seedlings and
because slurry also possesses anti-disease, anti-cold properties (Zhicheng, 1991 cited by
Lakshmanan, 1993:50), it holds promise as an effective seed coating medium (Lakshmanan,
1993:5).

Preliminary research in bioslurry use in seed treatment (pelleting, soaking, spraying, dressing, etc.,)
as well as control of insects in stored grain have been carried out in the past few years. Shen (1985)
reports that spraying digested slurry only or with little pesticide can effectively control red spider
and aphids attacking vegetables, wheat, and cotton. The effect of effluent with 1 5-20% pesticide on
controlling pest is the same as the pesticides. In this sense there is potential for biogas slurry to
reduce cost of production and pollution (Kate, 1991:13). Shen (1988) has also shown that basal dose
of barley seeds with anaerobically fermented sludge can very effectively control the barley yellow
mosaic virus which is one of the most destructive diseases in barley growing areas of India. It has
been estimated that barley yield can be increased by 20-25% by the destruction of 90% of the virus
in this way. It is achieved because slurry dressing prohibits large amount of pathogens and eggs
from entering into the seed by creating slurry coat around the seed and by producing volatile
substances as methane and ethyiene which form a protective layer around the coat. The higher
formation (than in the control) of Vitamin B 12 and hormones like auxinns, kinins, and gibberlins in
the treated plants also offer resistance to diseases (Kate, 1991:15). Seeds pelleted with 20% digested
slurry was reported (Lakshmanan, 1988) to have given higher okra (bhendi) pod production in India.
Seed pelleting in blackgram using effluent slurry at 50% w/w is reported to have increased yield by
35% over control (Kate, 1991:15).
Preliminary studies carried out at Annamalai University in South India during 1989 indicated the
suitability of bio-digested slurry as seed coating medium for rice and pulses (Lakshmanan et al.,
1989). Confirmatory trials were conducted during 1989-92 in rice, sorghum, soybean, blakgram, and
greengram. Following results were obtained

45
Rice:

Table 55: Effect of seed coating with biogas slurry on rice yield South India
Treatment Grain Yield (t ha -1) Straw Yield (t ha-1)
Wet slurry Dry slurry Wet slurry Dry slurry
Control 4.87 4.22 6.52 5.64
Seed Coating with: A 41
Biogas slurry 50% + Azospirillum 1%
Azospirillum 1% 5.14 4.43 6.87 5.78
Zn SO4 2% 5.51 5.50 7.16 7.04
Biogas slurry 50% + Azospirillum 1 %
Biogas slurry 50% +ZnSO4 2% 5.28 5.21 7.16 7.20
Azospirillum 1 % + ZnSO4 2% 5.65 5.77 7.52 7.69
Biogas slurry 50% + ZnSO4 2% 5.74 5.93 7.61 7.45
+ Azospirillum 1%
Gum Arabic 1% 5.91 6.19 7.49 7.64
0.6! 0.23 0.15 0.18

Source: Lakshmanan, 1993:7

Coating with bio-digested slurry at 50% + azospirillum at 1% + Zn SO4 increased grain yield by
1,04 and 1.97 t ha-' over the uncoated in wet and semi-dry conditions, respectively, inclusion of
ZnSO4 in the slurry medium gave more yield than slurry alone. Coating with digested slurry alone
gave more yield than the uncoated in both wet and semi-dry conditions. 'Increased yield in slurry
coated seeds might be due to the supply of readily available ammoniacal nitrogen and micro
nutrients from bio-digested slurry' (Lakshmanan, 1993:7).

Sorghum (Sorghum bicoior):

Table 56 provides data on the effect of seed coating with bioslurry on sorghum yield

Table 56: Seed coating in sorghum Tamil Nadu, India

Treatments Grain yield (t ha -1)
Seed coated with:
Biogas slurry 50% (w/w of seed) 2.36
Biogas slurry 50% + Zn SO4 1% 2.49
Biogas slurry 50% + Azospirillum 2.57
Biogas slurry 50% + ZnSO4 + Azos. 1% 2.66
Uncoated 2.32
Critical Difference (p = 0.05) 0.08

Lakshmanan, 1993:7

Seed coated with bio-digested slurry 50% + Zn SO4 I % + azospirillum 1 % registered the maximum
grain yield of 2.66 t ha-1, which was 14.66 and 12.71% higher than that of the uncoated and coated
with bioslurry alone, respectively. Inclusion of either azospirillum 1% or ZnSO4 1 % in the coating
medium gave similar effect on grain yield. Coating of bio-digested slurry alone did not influence on
grain yield.

46
Soybean:
In soybean, seed coating with bio-digested slurry, superphasphate, rhizobium, and phospobacteria
gave the additional grain yield of 0.64, 0.22. and 0.91 t ha-1 in clay loam, sandy clay loam and sandy
loam soils, respectively.

Blackgram and green gram:

Seed coating with bio-digested slurry and di-ammonium phosphate recorded the additional grain
yield of 0.47 and 0.59 t ha'' over the uncoated in blackgram and green gram, respectively. Seed
coating with bio-digested slurry, azospirrilum and ZnSO4 increased the grain yield by 1.04 and-
1,97-1 ha ' in rice over the uncoated in wet and dry conditions respectively

Seed soaking with biogas slurry:

Zhicheng (1991:46-48) reports from China that seed soaked slurry improved germination rate,
developed into better plants that were greener and less susceptible to disease.

Rice or wheat seeds were packed in plastic-knitted bags. The mouth of the bag was closed by a rope.
In addition, the bag was roped in several circles to avoid bursting. The seed bags thus prepared were
hanged submerged in the slurry of a running hydraulic anaerobic digester (48 hours for rice seeds
and 5 hours for wheat seeds). Seed was soaked in the fresh water with the similar procedure. The
results are presented in Table 57 below.
Table 57: Efficiency comparison of seed coating with digester slurry and fresh water (rice)
Soaking method Variety Soaking quantity Duration for Sprouting rate % Sowing
% germination (days) quantity
(kg/mu)
Digested slurry Cuangyoqgsing 5 5 98 0.85
Fresh water Guangyoqging 5 8 89 1.00
Source: Zhicheng, I 991:47 1 mu = 0.667 ha

As the above table shows, the time required for sprouting of the seeds soaked in digester slurry was
less than that of the seeds soaked in fresh water, the budding rate of the former was 10% higher than
that of the fatter. The sprouting rate for digester soaked seed is higher thus the amount of seed
required is reduced. In addition, following advantages were observed
• Strong and uniform budding
• Better development of roots
• Seedlings with green leaves and strong stem
• Seedlings resistant to diseases and pests as well as cold
• Higher survival rate of seedlings
(Zhicheng, 1991:46)

Another experiment was conducted in China with slightly different treatments. Table 58 below
presents data from this experiment

47
Table 58: Comparison of results of different seed soaking methods (wheat)
Treatment method Sowing area Variety Survival of seedlings Seedling
(mu) survial rate
(%)
Actual Seedling/mu
seedlings
Seed soaked with Digested 0.105 Nongqi 1.922 18.30 99.8
slurry Digested slurry + 0.105 Nongqi 1.620 15.40 84.1
yield increasing bacteria

Fresh water 0.105 Nongqi 1.467 13.92 76.2

Source: Zhicheng, 1991:47 1 mu = 0.667 ha

The fresh water treatment showed the lowest (76.2%) survival rate. Following explanations were
provided for this performance of digester soaked seeds:

• In a normally running and functioning digester, the slurry formed is usually rich in soluble
nutrients which are demanded by crops for their growth and development.

• There are numerous active substances (enzymes and vitamins secreted by microbes) present
in the slurry which promote metabolism and growth of seedlings. In addition disease
resistance and cold tolerance is developed and a better foundation for the somatic
functioning of genes is established.

• Because of large amounts of ammonium ions in the slurry, pathogen and worm ova are
removed from the surface of the seeds. In addition digested slurry in relatively free from
pathogens and parasitic ova.

• Soaking in the digester temperature favours the normal physio-biochemical changes in the
seed as compared to the ambient temperature outside the digester subjected to the seed in
fresh water soaking (Zhicheng, 1991:47-48).

In India, Kanwar et al. (1993:10-1 1) reports the results of a laboratory experiment on the influence
of biogas slurry on germination and early seedling growth of bread wheat The experiment involved
the following treatments:

• for slurry treatment, seeds were packed in cloth bags and dipped into slurry of a running
hydraulic anaerobic cattle dung digester for 6, 9 and 12 hours.
• seeds of bread wheat were soaked in fresh water for 6, 9, 12 hours

• the slurry thus treated were surface washed with running water to remove slurry adherents
from the surface of the seed.

The results reported were:

Germination:

• Treatment of seeds with water and slurry resulted in significant increase in germination
percentage as compared to untreated seeds. Seeds treated for 6 hours with slurry showed
highest germination percentage. Other soaking durations were also at par statistically.

• Slurry removal after 6 hours soaking resulted in reduction in germination percentage.

48
 • Mean germination time was significantly reduced by water and slurry treatments. Slurry
treated for 12 hours was effective In a pronounced way (water treatment for 6 to 9 hours
was also equally effective).

• Removal of slurry from seeds resulted in increased mean germination time particularly at 6
and 12 hours duration.

Root Length

• Root length of seedlings raised from slurry treated seeds increased significantly. Slurry
treatment resulted in maximum increase in mean value of root length as compared to water
treatment.

• Removal of slurry, after 6 and 9 hour of soaking caused reduction in its promotory effect on
root length.

• Kanwar et at. (1993:! 0-12) also report about a relatively more sophisticated experiment on
the effect of bioslurry as a dressing agent on the performance of rice an maize involving the
following treatments.

• For slurry treatment, seeds were packed in cloth bags and dipped in an anaerobic digester
(fixed type biogas plant) operating on cattle dung (for 12, 24 and 48 hours).
• Seeds of maize and rice were soaked in the fresh water for 12, 24, 48 hours.

• The slurry -treated seeds were surface washed with running water to remove any surface
adherents of slurry from the seeds.

Results

Germination

• All the treatments increased germination except untreated controls.

• Biogas slurry was less effective and rather its removal from seed surface resulted in slight
increase in germination.

• Twelve hours time was better than other soaking duration.

Mean Gemination Time (MGT)

• MGT is reduced by 12 and 48 hours soaking duration in maize and 48 hours in rice.

• Removal of slurry from surface of seeds did not yield any significant effect on MGT.

Mean Root Length (MRL)

• Slurry treatment of 48 hours resulted in significant increase in MRL (Maize).

• In rice, slurry treatment proved to be less effective than other treatments as long as MRL is
concerned.

49
Mean Shoot Length (MSL)

• MSL increased significantly in all the treatments (maize)

• No significant increase in MSL in slurry treatment (maize)

• Removal of slurry did result in slight increase in MLS (maize)

• In rice air the treatments increased MSL but the MSL increase in slurry treated seed did not
override the influence of other treatments

Mean seedling length of pot grown plants

• Treated seeds grown in soil showed better growth of seedlings in comparison to control.

• However slurry and water treated seeds did not differ in mean seedling length.

• The removal of slurry from seeds did not effect seed performance.

On the whole, it was found that the application of slurry significantly improved the seed
performance over untreated seeds but its effect was equal or less pronounced than water treatment.
When slurry was rinsed-off before germination its germination value increased. This finding
contradicts the earlier finding of Zhicheng (1991) in China in which digested slurry treated rice and
wheat seeds showed pronounced effects over seeds soaked in fresh water. Kanwar et al. have
observed that removal of slurry from seed surface caused improvement in seed performance in
relation to some parameters which indicated "slurry application for longer duration and its
persistence on seed may prove to be futile or less effective for seed growth' (Kanwar et al., 1993:12).
However, it is also plausible that the Chinese experiment (Zhicheng, 1991) did not involve surface
washing with running water to remove surface adherents of slurry from seeds and it might well be
the reason behind the better performance of slurry treated seeds as compared to seeds treated with
freshwater. Anyway, Zhicheng's (1991) findings could not be confirmed. Of course, Kanwar's (1991,
1993) experiments included design to incorporate these concerns. The findings are far from being
conclusive.

Use of biogas slurry on the prevention and cure of crop diseases:

Very few research works have been carried out in use of biogas slurry in desease/ pest control. Some
of the preliminary results are reviewed below.

Control of rice diseases and pests

An experiment was conducted in 1988 in Hunan Province of China to see the possible effects of
biogas slurry in controlling some of the rice diseases and insect pests (Jiasi et al., 1991:49-52). The
effect of fertilising with slurry and urea was compared to fertilising with human faecal matter and
ammonium carbonate and urea fertilization. Slurry fertilizing proved superior, in some cases, far
superior, in reducing disease ( mildew, helminthosporium, sigmoideum) and in restricting attacks by
insects (leaf weevil, rice weevil). The yield was also higher than that given by the control.

50
Wheat gibberella disease

An experiment was conducted in the Shanxi province of China where (Zhengshan, 1992:24-27)
wheat gibberella disease used to occur, sometimes seriously. Biogas slurry was taken from the outlet
of the normal biogas digester treating human and animal wastes. Two control tests were carried out,
one using clear water and one using a pesticide. The results of the slurry test corresponded
approximately to those of the pesticide test. More specifically, the incidence of wheat gibberella
disease was reportedly 20% lower than the contrast; relative effect of prevention and cure increased
by 45% which was similar to Bavistin. It was also concluded that best effects could be obtained by
spraying undiluted biogas slurry @ 50 kg/mu (75Ot/ha). in this way both pesticides cost could be
served and pollution caused by these pesticides be reduced.

Control of storage insects

Use of chemical fumigants to control storage insects and pests have their own sets of disadvantages.
Residual effects, handling hazards, resistancy development etc., are the disadvantages that are often
cited. Even the practicality of CO2 as a fumigant is hampered by the availability of containers and
other requirements at farmer's level.

Effectiveness of biogas as a fumigant for control of pests during storage of paddy has been
demonstrated under laboratory conditions (Biogas Forum, 1994:15-16). In India, study was
conducted by Mohan et at. {1992:229-232, excerpted in Biogas Forum. 1994) on the use of biogas
from cow-dung for insect control during storage.

A leak-proof bin of 100 kg capacity was developed for biogas fumigation. The bin was made of a
special type of PVC. It was rectangular in shape with a circular top position closed with a removable
air-tight lid. The biogas inlet gate valve was fitted at three quarters height of the bin so that the space
below the Inlet value could be filled with pigeon pea seeds and the remaining space at the top would
be occupied by biogas. An outlet was provided in the lid to facilitate checking for the presence of
biogas.

The testing was carried out on 100 kgs of grains placed in the bin and supplied with biogas at 1.4
kg/cm2 pressure

Result:
• It was found that there was significant difference in insect mortality between 3, 5, 7, 10 and
12 days of fumigation at different layers of stored grain.

• One hundred percent mortality of eggs, grubs and adults was found on the 10th and 12 th
days of fumigation.

• For adequate penetration of the biogas at different layers a pressure of 1.4 kg/cm2 should
be applied for a minimum of 10 days.

• An analysis of treated grains showed no significant amount of CH+ residues.

It was concluded that these findings hold great significance for the future of agricultural produce
storage. However, more research is needed in this area. As the editor of Biogas Forum (1994:15-16)
rightly comments, it will be difficult for a farmer to create a pressure of 1.4 kg/cm2. Further research
into the possibilities of prolonging the fumigation period with lower pressure is perhaps the needed
research agenda at this stage.

51
Foliar dressing with effluent slurry:

In China, foliar dressing with effluent slurry gave better crop yields than dressings done with
chemical fertiliser alone {Shen, 1985). Foliar dressing provides both nutrition as well as moisture.
Perhaps these may be the reasons for improved yield performance.

52
 Chapter 4

Sanitation and Public Health Aspects of Slurry Utilization in Crop production

4.1. Preliminaries

Environmental benefits of biogas technology in terms of reduction of fuel-wood dependency and

soil erosion, etc., have been discussed and reviewed in numerous publications. The same is the case
with environmental consequences of chemical farming in general and excessive chemical fertilizer
use in general (e.g. Shiva, 1988). The betterment of household sanitation, in terms of human and
animal waste disposal and smokeless kitchen and its positive effects on health, has been frequently
written about and commented upon in the context of biogas technology, in addition, the practice of
utilizing organic manure including manures from biogas plants (as the earlier chapters showed) are
frequently taken as ' environment friendly', ' natural7 and as a part of ecological agriculture that
presumably has better sustainability as compared to chemical agriculture which is largely dependent
upon non-renewable energy resources. This review will not delve into these areas because an
extensive attempt to review will have to include. The existing general, interrelated literature ranging
from the romantics (e.g, Walt Whitman1 and latter, Walden Berry (1976,1977), to empirico-
romantics (e.g., Fukuoka of the One Straw Revolution fame) to environmentalists of anti - modernist
pursuits and even post -modernists. The literature in this sense is already too much voluminous.

In addition, the following review will also deliberately exclude public health and sanitation aspects
of the contamination of biogas slurry with toxic organic compounds (e.g. halogenated organic
compounds and polycondensed aromatic compounds), heavy metals, and radioactive substances.
These contaminations at present cannot be a source of major concern to small operators in
developing countries like Nepal because of the nature of the feedstocks used (generally livestock and
agricultural waste matter). The highest risk of heavy metal contamination of bioslurry exists for
those plants that process waste water x a substrate proceeding from certain industrial plants (e.g.,
metalworking, electro-chemical industry, paints and dyes) (Kone, 1991:10). Plants designed for the
treatment of the municipal sewage can be exposed to critical concentration of heavy metals, which
prohibit the utilization of bioslurry as manure on cultivated farmland (bid). The immediate concern
in Nepal and many developing countries are related to the sanitation and public health aspects of
biogas slurry derived predominantly from animal, human and agricultural wastes.

it is obvious that that most epidemic diseases in the rural areas of the third world countries result
from dirty water and poor management and disposal of excreta. The latter is even more important
since poor disposal of excreta may cause the pollution of water source and the breeding flies which
are media for the spread of diseases. If the untreated excreta are directly used 2s fertiliser, pathogens
in them easily spread (APRBRTC, 1983:161).

4.2. Excreta born diseases and organisms

Numerous viruses, bacteria, nematodes and fungi are present in human and animal excreta. As will
be seen the number organisms reported are more in human than in animal excreta. Table 59 below
presents a compilation of types of organisms and the diseases associated with them.

1
This American icon has even a poem called 'This Compost1 besides 'The Leaves of Grass' to his credit-Readers with
poetic inclinations can refer to the Complete Biogas Handbook (d-House,1978:322')

53
Table 59: Excreta-borne organisms and diseases2

Common Name Scientific Name Disease

Helmimhiasis
Schistosoma Scnistosomiasis
S. mansoni, (Biha roasts}
S. japonicum
S. haemaiobium
Hookworm Nectar americanus Hook worm diseases
Round worm Ascaris lumbricoides Ascariasis
Tapeworm Taenia saginata Tape worm infestation (Teeniasis)
Thread worm Taenia solium Thread worm infestation
Stroglyloides stercoralis
Pin worm Enterobius vermiculoris Enterobiosis
Whip worm Trichuris trichuria Tnchuriasis
Selmonete ryphi Typhoid
Salmonella paratyphi A,B. or C Para typoid
Staphylococcus aureus
Pneumonia, boils, internal absecces
Pseudomonas aeroginosa Urinary tract infections
Escherichia coli Normally harmless but can cause gastro-
intestinal infection
Urinary tract infection
Proteus vulgaris Cholera
Vibrio cholerae
Infection of the urinary tract, gall
Citrobacter bladder, etc
Dirrhoea
Camoybacte

Shigella spp Shigellosis

S. dysenteriae Bacillory dysentery
Viral
Hepatitis A,B,CD
Polio virus Infectious hepatitis
Epstein Barr-virus Poliomyelities
Echoviruses
Coxsackie viruses
Reoviruses
Advenoviruses
Echoviruses
Rotaviruses
Protozoal
Entamoeba histolytica Amoebic dysentery
(Amoebiosis), ulcer of colon, liver
absecces

Giardia lamblia Diarrhoea and malaosorption

Balantidium coil Mild diarrhoea, colonic ulcer

Source: APRBRTC, 1983:162; Martin, 1994; Satyanarayana et al. 1986; Navrekar, 1986:53; Mapuskar,
1986:59-63, Khandelwal, 1986:108

2
This listing is not based on the analysis of a single human excreta sample. The organisms are reported by different authors. The list does
not include organisms specifically reported for cattle or buffalo dung. These will be provided in a separate table.

54
Table 60 was presented to show how potentially danger human excreta is if it is not disposed safely.
It is obvious that these parasites/ pathogenic organisms may not be present in one sample at a time at
a place.

Biogas plants are obviously important for health and sanitation from the point of view of organised
disposal of animal and human wastes. They are even more important in situations where toilets are
not constructed and defecation in the open spaces are accepted norms as in many parts of South
Asia. A quote from India is pertinent here

".... our people are yet to accept the use of biogas plants
with latrines connected. As per Manusmriti, it is stated that
latrine should be located 400 steps away as defecation is
considered dirty. In the conventional communities orthodox
people visit latrines by putting on separate clothing. The
Mohejodaro excavations have revealed the provisions of
bathroom and drainage but not of latrines, implying thereby
the prevalence of open defecation which corroborates belief
in Manusmriti" (Patel, 1986:26)
In India it has been reported that human wastes are responsible for 80 percent of the diseases (Dayal,
1986:3). Even if this single source is responsible for half of this percentage of diseases, that is a
matter of grave concern, in India, below I percent of the rural population reportedly enjoy sanitary
facilities and 33 percent of the urban population have no toilet facilities (ibid). It has also been
reported that only 20 percent of the household are covered by sewerage. Only 14 percent of urban
households use latrines that are connected to septic tanks (Dhussa and Myles 1986:86). The situation
in the rural areas must be worst. The number of those resorting to defecating in open spaces is thus
enormous. It has been estimated that the resultant cost in terms of medical treatment and lost
production is around Indian Rupees 4.5 billion per annum (Dayal 1986:3). Statistics are not
available, but no one is in the position to say that the situation is better - off in Nepal.
Similarly, it is not unusual to find human and animals living almost together in smaller farming
households. Spreading of pathogens to humans under these circumstance is easily understandable.
Adoption of biogas technology not only leads to the formation of a sort of 1 clearing house' for these
waste materials subsequently leading to better sanitation and public health, it also reduces the
potentials and number of pathogens substantially so that when the digested output is used in
agriculture, sanitation conditions are improved and health risks reduced as compared to the practices
of utilising undigested animal and human excrete (or leaving them scattered throughout the
courtyards or open spaces near the homesteads).
The concern of this chapter is the health and sanitation aspect of biogas slurry (produced out of both
human and animal excreta) when it is used as fertiliser for crops.
The purpose in this review is to examine the extent of removal of these different parasites and
pathogens during anaerobic digestion.
4.3. Research in pathogen/parasite survivability
Shanta (1970 cited in Satyanarayana et al., 1086:14-15 ) carried out laboratory studies to determine
helminth parasites removal during night soil digestion at 37°c. Table 60 presents the results

55
Table 60 : Percent reduction of helminth ova in laboratory night soil digester

Loading Detention pH Influent Effluent % Reduction

rate time (days) No. Ova/ Litre No. Ova/Litre
Kg./VS
Ascaris Hook Ascaris Hook Ascaris Hook
worm worm worm
2.21 20 7.50 4000 58200 2080 21360 48.0 63.2
1.78 25 7.60 114000 18200 38324 1639 66.5 90.6
1.45 30 7.65 94110 21820 28248 1528 70.0 93.0
Source;-Satyaiwayana-et.al.,.1.98-6:15

The table shows that ascaris eggs survive for longer period than hookworm. In the case of
hookworm, 90% of ova is reduced as compared to 70% reduction in ascaris ova in a 30 days
detention period. These parasite ova are removed to the extent of 67% and 91% respectively at a
detention period of 25 days. It has also been observed that the sludge and supernatant still contain
viable eggs. Prolonged use of thermophilic digestion process may result in lysis of the micro-
organisms and also results in the destruction of pathogenic bacteria as well a parasitic ova in the
night soil (Henze et al. (ed.) cited in Satyanarayana et al., (1986:9).

From public health and sanitation aspects, Kshirsagar (1986:37-43) presents a profoundly cautious
interpretation of the available information on biogas slurry produced from human excreta. He gives
the warning that "night soil-based biogas plants which are being propagated as a health protection
and energy conservation measure may themselves turn out to be the source of dissemination of
diseases unless utmost care is taken at all stages". He further warns that "if the nightsoil is to be
manually collected from elsewhere for feeding into the digester the scavengers come into direct
contact with pathogens. It is possible for the pathogens to survive in large numbers in the digester
and pass over to the effluent. Anaerobic digestion over merely 30-50 day's detention time is
unhelpful for pathogen destruction. Even the drying of effluents removed after this insufficient
detention time does not help in making the manure innocuous. There are great hazards if the crops
grown with such manure are eaten raw. The use of sludge on crop lands or in fish farms suffer from
higher incidence of infections of helminthic and intestinal pathogens, the workers on sludge- fed
forms, too, are likely to be victims;/(ibid).

Kshirsagar (1986:38) justifies his argument of the persistence of pathogenic organisms in the
digested effluent as follows:

".... conditions in biogas units are much the same as are prevalent
in the biogas of living human beings. These conditions are taken
advantage of by the pathogenic organisms discharged by sick
persons or by the vectors which are thus potentially present in the
feed to digesters. Obviously these pathogens will survive in the
digestion processes in large numbers. Some reduction would, of
course, occur due to attack from predators. Thus, the process of
anaerobic decomposition even if carried out in a controlled manner
is not helpful in destroying pathogenic organisms within the
detention period of 30-35 days normally deployed. Hence the
effluent slurries coming out of the nightsoil fed biogas units will be
equally hazardous to handle, dispose of or utilise in the field as
manure."

56
Kshirsagar argues that some of the pathogenic organisms (e.g. those of amoebic dysentery) which
can form cysts or the eggs of some of the helminths will remain "totally unaffected" while passing
through the anaerobic digester. For agricultural use sun -drying (for 10-20 days) is recommended.
Even with this some of the pathogens survive. He suggests that farmers working even with dried
slurries (cakes) should be advised to use protective gears.

According to Chanakya (1986:45) the optimum time of 35-52 days used in the conventional dung
based plants will not hold good for digesters designed to be run on night soil because during this
retention period many pathogens present in night soil will still be viable and it would be dangerous
to discharge such effluents.-into the open permitting human handling and exposure to vectors of
decease transmission. The design of the plants needs to be modified so that pathogens are retained
(or inactivated) within the digester while only the excess water and spent solids are discharged for
secondary treatment. According to Navrekar (1986:52-56) if the actual retention time is low, the
effluent from aquaprivies and septic tanks and even from conventional sewerage treatment plants
contain a high percentage of viable pathogens. Only the biogas plant system has the potential
system; in that too, only the fixed fixed-dome system with a composting complement, is considered
ideal.

The ova of helminths are reported to be denser than the night soil slurry. During liquefaction phase
the ova settle down at the bottom. Within 20 hours, 95% of the ova get settled. The hookworm ova
survive only for nine days under anaerobic conditions and those of schistosoms and ascaris can
survive up to 10 days. If the ova get separated perfectly they can be retained at the sedimentation
space below the outlet pipe. The ova can be retained at this space for more than 100 days causing
their deactivation. Similarly, bacteria like Salmonella spp, Shigella spp, Vibrio cholerae,
Mycobacterium tuberculosis, that are commonly spread through faeces, cannot survive when
subjected to anaerobic condition at 22 - 37° for about 20 days (range: 6 to 20 days) (Navrekar,
1986:56).

When the effluent/sludge come from biogas plants, the remaining chances of pathogen survival is
completely reduced. The temperature of 50° to 60° C, generated in a properly managed compost,
kills the pathogenic flora within a short period of time.

Tables 61 .a. below presents data on the survivability of a number of organisms during anaerobic
digestion and in the sludge.

Table 61. a.: Survival time of pathogens in some excreta disposal system
Organisms Pit and composting latrines Anaerobic digestion at Survival time in sludge
with 3 months retention 32°O 35°C
Enteroviruses Less than 3 months 28 days 3 months
Bacteria
Salmonella typhii Salmonella -do- 4-5 weeks 1 month
paratyphii Shigella -do- 4-6 weeks 1 month
Vibrio choierae -do- 9-10 days 1 month
Pathogenic E. Coli -do- 7-14 days 5 days
-do- 4-8 days 5 days
Protozoa
Entamoeba histolytica Giardia -do- 3 weeks 2 weeks
lamblia Balantidium Coli -do- -do- -do-
-do- -do- -do-

Helmiths
Ascaris lumbricoides Ova survive Ova survive Ova survive
Enterobious -do- -do- -do-

57
Vermicularis
Ankylostoma dudenale •do- -do- -do-
Strongyloides •do- -do- -do-
Sterooralis
Taenia saginata -do- -do- -do-
Taenia solium -do- -do- -do-
Trichuris trichiura -do- -do -do
Source: Mapuskar, 1986:63

The table shows that with a digestion temperature of 32-35 degree centigrade most organisms are
eliminated but the helminth ova survive in this temperature and retention time. This has
consequences for the adjustment of the retention period as well as temperature to be maintained
within the digester. Perhaps the design aspect is linked with these adjustments.

Table 61 .b. below provides a detailed picture of the relationship between temperature, retention
time and the magnitude of pathogen/parasite elimination.

Table 61 .b.: Temperature, residence time and die-off rate of parasites and pathogens
Organism Category Temperature °C Residence time Die-off (%)
(Days)
Poliovirus Viral 35.2 2 98.5
Salmonella spp Bacterial 22-37 6.20 82.96
Salmonella typhosa -do- 22-37.6 6 99
Mycobacterium
tuberculosis -do- 30 Not reported 100
Ascaris Parasite Helminthic 29 5 90
Cysts -do- 30 10 100
Source: Gupta, 1986: 69

The table is self-explanatory. With a digester temperature of 37.65 degree centigrade and a retention
period of ten days organisms listed in the table are eliminated.

If these are based an accurate analysis, adoption of biogas plants and the prospects for the use of
slurry for crop production is bright from public health and sanitation aspect. Composting of
slurry/sludge is claimed to further reduces any chance of the pathogen spreading to the environment.
Table 62 below presents a comparison of pathogen survived in an unheated anaerobic digestion and
composting.

Table 62: Comparison of pathogen survival in unheated digestion and composting

Organism ln-unheated anaerobic digestion In composting
1. Enteric May survive for over three months Killed rapidly at 60°C
2. Salmonellae May survive for several weeks Killed in 20 hrs at 60°C
3. Shigellae Unlikely to survive for more than a few Killed in hr. At 55°c or in 10 dys at
days 4O°c
4. E-coli May survive for several weeks Killed rapidly killed above 60°C
5. Cholera May survive for one or two weeks Killed rapidly 55°C
6. Lepotospire Survive for not more than two dys Killed in 10mts.AtS0°C
7. Entamoabacysts May survive for three weeks Killed in 5 mts at 50°C and 1 day at
40°C
8. Hookworm ova Ova will survive Killed in 5 mts at 50°C in 20 hrs. At
50°c and 200 hrs 45°C

58
9. Ascaris ova Ova will survive for many moths Killed in 2 hrs. At 55°C in 20 hrs. At
50°C and 200 hrs 45°C
10. Schistosome Ova may survive for many months Killed in 1 hr 50°C
11. Taenia ova Ova will survive for a few months. Killed in 10 mts. At S8°C and in over 4
hrs at 45°C
Source: Navrekar, 1986:57 mts-minutes; hr-hour

The reports are contradictory at times. The retention time-temperature is a matter of lively debates
and controversies in India.

Singh (1986:65-66) reports that poliovirus 35° C is reduced by 98.5 percent within two days. Within
the temperature range of 22°-37°C, Salmonella lyphosa is reduced by 99 percent in 6 days.
Salmonella spp is reduced by 82-86 percent in 6-20 days. Mycobacterium tuberculosis is killed 100
percent at 30°C. All encysted helminths are destroyed except ascaris cysts which are able to survive
even after 14 days at 35°C. Ascaris cysts are completely digested during thermophilic digestion (48-
60°C). if digested slurry is dried and stored for about six months the ascaris cysts are destroyed even
if the digestion was achieved in mesophilic (below 40°C) temperature. Singh concludes that
anaerobic digestion of human excreta removes most pathogens and improves public health and
sanitation. With the storage of effluent in solid system, it can be used as manure with reduced health
hazards. Such a conclusion is also reached by Gupta (1986:69). He, however, notes that effective
destruction of pathogenic enteric microorganisms does not preclude the survival of at least some
micro-organisms of public health significance. But these organisms continue to die-off because of
the lack of nutrients and the hostile environment during storage, drying and application to the soil.
Contamination of crops by surviving pathogens is achieved by pasteurization in European countries
(ibid). However, in the Nepali and South Asian context as a whole, such a process is economically
not feasible. Khandelwal (1986: 105-109) is similarly optimistic about the potential of biogas plants
to eliminate pathogens. According to him pathogenic bacteria get killed if the actual retention time
in the digester is 14 days at 35°C. The die-off rate of enteric viruses reported is 22 percent at this
level of temperature and retention time. In line with the analyses and arguments put forward by
Navrekar, Singh, and Gupta, Khandelwal asserts that "there is no cost effective method which can
match anaerobic digestion in the destruction of disease producing organisms. Composting can kill
the most of the remaining pathogens" (Khandelwal, 1986:105). According to Khandelwal, use of
spent slurry not only improves soil fertility leading to increased agricultural production, it is also an
operation of waste disposal leading to better sanitation.

Khandewal reports that plate counts of spent slurry for micro-organism of the farm
manures and 107) in
human excreta samples showed the presence of highest number of bacteria (38 nightsoil.

Table 63 below presents a list of species of bacteria, fungi and other organisms in a sample of farm
manure and predigested night soil from India.

Table 63: Organisms isolated from farm manures and non-digested nightsoil
Group
Sample Bacteria Fungi Others
Night Soil Escherichia coli Rizopus Ascaris
Proteus vulgaris Penicillium lumbricoides (eggs)
Citrobaaer Aerobacter aerogines Aspergillus

Staphylococcus aureus
Salmonella paratyphi
Pseudomonas aeroginosa

59
Farm manures (poultry and Escherichia coli Rhizopus Actinomycetes
cattle dung) Citrobacter Peniciilium
Aerobaaer aerogenes Aspergillus
Pseudomonas Mucor
Bacillus Pilobolus

Source: Gaur et al., 1986:108

Some of these organisms are pathogenic while others are non-pathogenic normal commensals of the
gastro-intestinal tracts. However as shown earlier (Table 59), the list of pathogenic organisms in
human faeces reported by researchers is long. Even if the case with animal manures is the same the
number of pathogens reported are relatively low.

The review reveals that even in a country like India where biogas has received such an enormous
interest both at the policy levels and research institutions, there are still many unsettled issues
pertaining to health and sanitation aspects of slurry utilisation in agriculture. However, firstly, the
major issues on which consensus seemed to have reached among the scientists are as follows.
• On-site disposal systems for human waste through anaerobic digestion are best suited for
India. Anaerobic digestion in a biogas plant is hygienically a very promising and desirable
system

• Plants designed for human waste should give primacy to hygienic considerations.

• Raw human wastes should not be manually handled

• Undigested or semi-digested nightsoil should not be exposed to surroundings. Care must be

taken to see that insects or animals do not get access to it.

• Pathogen survival time in the effluent slurry should be the primary concern in the design of
biogas plants. Only these designs which fulfill health parameters (i.e. maximum pathogen
elimination) should be permitted for wider adoption.

• The benefit cost ratio of nightsoil biogas plant operations should be increased by gas
production efficiency and by optimizing manurial value. This should be done by
considering
public health aspects as the first requirement of a nightsoil biogas plant.

• In terms of quantity, human waste is an important resource of plant nutrients, next only to
animal waste.

• Spent slurry is rich in nitrogen but drying is considered not a desirable method

• The idea of enriching slurry with rock phosphate, superphosphate and preparation of

• organo-mineral biofertilizer should be systematically explored.

60
 • Preliminary tests show that the addition of 15% ammonia solution to the spent slurry kills
pathogens. This needs to be systematically explored.
• Further studies on survival of pathogens in the digester as well as during application of spent
slurry in agricuiturai fields and fish pounds need serious considerations due to the
importance
of the manurial aspects of slurry in the total biogas system.
• Suitable mechanical devices should be developed for handling the effluent
• Field trials need to be conducted on the use of different forms of slurry from different
feedstocks for manuring in agricultural fields and fish ponds.
• Spent slurry from excreta fed plants can be used for manuring crops after adequate dilution.
It can be used for composting other organic wastes.
• Effect of spent slurry from excreta fed plants on physical, micro-biological properties of
soils
including health and sanitation, socio-economic benefits and costs need to be studied further.
• Adoption of a multi-disciplinary approach {health, sanitation, agriculture, forestry, fisheries
etc.) has to be evolved to facilitate a package approach in slurry utilisation.
• Mass awareness on the various aspects of the excreta fed biogas should be created.

• Major disagreements

Those who support nightsoil based biogas plants keep on arguing that whatever the
imperfections and the resulting hazards, the situation will be better than open defecation. Others
claim that human faeces based effluent slurries are not quite free from pathogens, and that by
virtue of its fluidity spread the contamination to the wider environment. Researches belonging to
this camp also agree that nightsoil's biogas potential, however great per unit of excreta, is
negligible in the total because the per head output of human faeces is only one twentieth (or even
less) of the cattle's per head output of dung. This potential is considered to be insignificant in
comparison with the total nutrient potential of biogas from cattle and plant wastes. This ' little
amount of methane' is considered not worth the risks of faecal effluent slurry, which could
pollute a greater mass than the solid excreta ever could. It has been agreed that sanitary disposal
of excreta can be achieved by other means such as anaerobic composting of four to six months'
duration or aerobic composting of four to five week's duration. Because composting is recycling
as far as nightsoil is concerned "let us not aspire for gas from night soil because the faecal slurry
produced in the process is far from safe" (cited by Ghosh, 1986:135).

Disagreements on specific scientific and technical Issues:

Hydraulic Retention Time (HRT), temperature and pathogen survivability:

Wider differences in opinion with regard to the HRT is evident among the scientists involved. HRT
is linked to the survivability of pathogens which in turn, has consequences for the utilization of
slurry as manure.

Satyanarayan et al. (1986:23-25) claim that "at an average digester temperature of 28°C, some 67%
ascaris and 90% of hookworm eggs were destroyed during a retention period of 25 days." Parikh
(1986:74-77) on the other hand claims that ascaris eggs "neither grow nor die at 27°C for 40 days",
and that parasite eggs can survive for 15-40 days at 2O-3O°C temperature." Gaur and Khandelwal
(1986:105-109) claim that pathogenic enteric bacteria are killed if their actual retention time in the
digester is 14 days at 35°C. The die-off rate of even the enteric viruses is reported to be 22% at this
level of temperature and retention time. Chanakya (1986: 100-102), on the other hand, reports that

61
enteric viruses can persist for 180 days at 2O-3O°C and considers that retention time of 35-52 days
insufficient for night soil digesters. Gupta (1986:68-70) claims that a retention time not shorter than
14 days at a temperature not significantly lower than 30C, to be sufficient reasons that at this level of
operation, pathogenic enteric micro-organisms, with a few exceptions, are effectively killed. He
argues that since pathogens, in any case, cannot be destroyed hundred percent and that effluent
should be and can be effectively utilised because most pathogens are destroyed during digestion and
remaining few continue to die off due to the hostile environment in which these organisms cannot
receive appropriate nutrients!

Such a lower retention time is opposed by Dhussa and Myles (1986:86-89) who claim that night soil
must remain in the plant for at least 70 days to become free from pathogens and parasitic ova. Since
public health is of overriding concern, and since it is difficult to exercise control over millions of
individual households' practices of composting etc., it is better to exercise utmost control in the
digester design itself, most importantly, by fixing the HRT on the basis of winter temperature. In this
context the digester's volumetric capacity should also be increased (Ghosh, 1986:139). Mapuskar
(1986) however does not favour this approach because the costs involved will be a deterrent for
biogas adoption. According to him a retention period of 40-45 days at 32-35°C eliminates the viral,
bacterial and protozoa! pathogens; the helminth ova settle at the bottom of the digester.
Mapuskar claims that ascaris ova survive in the slurry after 30 days of anaerobic digestion at 32-
35°C and even thereafter in the sludge (in contrast to Gupta's (1986) claim that a 90% die-off of
heiminthic ascaris within 15 days at 30°C). Even then there is no reason to extend the retention
period beyond 40-45 days. It could even be reduced to 25-30 days if retention of effluent for 25-30
days in an adjacent pit for secondary treatment is assured (Mapuskar, 1986: 81-85).

On the application of slurry:

Gaur and Khandelwai (1986:105-109) seem to have no objection on the direct application of slurry
(without drying) provided that the land is ploughed immediately after slurry application. In this
process ammoniacal nitrogen is saved for use by plants. In addition, plants receive moisture from the
slurry. Gaur and Khandelwai also argue (mentioned earlier) that slurry can be mixed with either
solid crop residues, farm and city organic wastes, or mixed with already humified compost for
maturity before transfer to fields. They also report that slurry can also be composted with phosphatic
fertilisers to reduce the loss of ammoniacal nitrogen.

However the uses of fresh slurry out of excreta fed biogas plants is fraught with technical
controversies. Gaur and Khandeiwa! was (like Mapuskar) seem to think that the unfavourable
environment as well as soil microbes would kill the remaining pathogens in the spent slurry.
Kshirsagar's (1986: 37-43) position in this issue was reviewed in detail earlier. He is extremely
cautious about the use of fresh slurry from human excreta fed biogas plants as manure. According to
him "if labourers working on sewage farms are having a high incidence of infections from
helminthic and intestinal pathogens, the workers who would be working with effluent slurries, too,
would certainly be vulnerable. Lack of data in this respect cannot be construed as a positive
indication of safety in handling and using this material (i.e. sewerage and nightsoil sludge for
fertilising land and fish farms)" (p. 39). Kshirsagar thus argues for sun-drying or aerobic composting
of effluent slurry. It has also been reported that enteroviruses can come out prematurely and can
cause epidemic, and also that pathogens from raw nightsoil can penetrate the cell wall barriers of
plant root systems and get into human found sources. Logically, then, for him, it seems plausible that
if pathogens from raw nightsoils can penetrate the plant cell and enter human food sources, pathogen
remaining in spent slurry may also be able to do the same (Ghosh, 1986:141).

62
Thus it seems that convincing data to those differences are lacking, it should also be noted that
engineering aspects of biogas plants have been receiving better attention than the microbiological
aspects in India. Ghosh has gone to the extent to state that "perhaps it is not microbiology alone,
questions of science in general have been side stepped (Ghosh, 1986:141).

The process of elimination of pathogenic ova:

The Chinese rely on the sedimentation procedure to eliminate the ova of some of the important
pathogens present in manures and faeces (APRBRXC, 1986).

According to the Chinese reports, the specific gravity of the effluent in the digester is generally
1.005-1.010 as compared to 1.055-1.060, 1.140 and 1.200 of hookworm, ascaris and schistosome
ova respectively. As the specific gravities of the ova of these common parasites are heavier than that
of the effluent in the digester, these ova sink spontaneously due to their own weight, to the bottom of
the digester. Table 64 below presents the settling down time of some of the common ova in a 1
meter deep liquid manure.
Table 64: Settling time of some of the common pathogenic ova
Pathogenic Ova Setting time (hours)
Schistosome (mostly) 2
Ascaris (mostly) 8
Hookworm (45.77%) 4
Ova of all three (96.6%) 20
Source: APRBRTG 1986:165

Some ova remain floated in the upper layer. Very few remain suspended in the middle layer. On the
whole 95% of the total ova can be found in the sedimented residue. The middle layer is used as
fertilizer. All the faecal sediments are left in the digester. Thus, one can see that the number of ova
in the effluent is reduced by 95% in comparison with the excreta in the inlet pipe. Ova left in the
residue is killed by disinfection and this residue then is also used as fertiliser. Thus, in terms of
design, the digester with middle layer outlet is better than one with discharge chamber.

Pathogen survivability, HR.T and temperature:

Table 65 below presents summaries of experiments carried out in these aspects in China. The
experiments involved putting live schistosome ova in a nylon net bag and placing the bag into a
fermenting task.

Table 65: Survival periods of schistosome ova

Ova survival Season

period in the digester (days)
7- I 4 days Summer
15-22 days Autumn
26-40 days Winter
Source: APRBRTC, 1986:169

63
Table 66: Fatality rates of hookworm ova
Retention period (days) Fatality rate {%)
6 40
30 90
60 99
90 100
Source: APRBRTC, 1986:169

Table 67: Fatality rates of ascaris ova (summer and autumn)

Retention period (days) Fatality rate (%)
18-1 7 12.5-44
100 30
Source: APRBRTC, 1986:169

From another experiment in China (APRBRTC, 1986:169) (using fermenting bottle under anaerobic
condition), it is reported that Shigella flexner lasted 30 days at 25°C and 100 days under aerobic
conditions (control). Both Salmonella typhi and Salmonella paratyphi lasted about 44 days under
anaerobic conditions and 98 days in the cooled boiled water (control).

From these studies it has been concluded that the treatment of excreta in the digester at the ambient
temperature is feasible in vast rural areas of China.

Chinese research works find that the optimum temperature range for the survival and growth of ova
range from 22-40°C.

Table 68 below presents data on the relationship between temperature and survivability of pathogen
ova as reported from researchers in China.

Table 68: Pathogen survivability under different temperatures

Organism Temperature Survivability

Ascaris ova 50°C Can live for 20 minutes
Ascaris ova 55°C Can live for 10 minutes
Ascaris ova 60°C Killed right away
Hookworm ova 15°C Can live for few hours
Hookworm ova S5°C Killed immediately
5crtistosome ova 45.5°C Can live for 2 hours
Schistosome ova 53°C Death occurs within one minute
Liplospira 50°C Destroyed within 10 minutes
Salmonella 55°C Killed within one hour
Salmonella 60°C Killed within i 5-20 minutes
Escherichia coli 55°C Killed within one hour
Escherichia coli 60°C Killed within 15-20 minutes
Source: Adopted from APRBRTC, 1986: 169-170
Studies by Garde et al. (1987:4-8) have shown that mesophilic anaerobic digestion results in complete
inactivation of Salmonella typhimurium in 10 days. It is also suggested that since in the Indian design of
biogas plants animal dung is digested along with nightsoil with a detention time of more than 30 days,
there is no possibility that Salmoneila typhimurium will survive in the digested slurry. Even
Enterobacteriaceae elimination under mesophilic anaerobic digestion is seen as a possibility.

64
It has also been reported that most viruses except hepatitis viruses may lose their activity at 60°C within
one hour.

From thermophilic3 and mesophilic4 experiments conducted in Shangdon Province in China, it is reported
that 98% of the ascaris ova died in one day, and 100% in two days. Schistosome, hookworm,
saimoneiia and shigelia ova were destroyed within 21 hours. In a smaller experimental digester,
Salmonella and shigella were reportedly killed within one day. Also 99.5% of ascaris ova were killed in
one day and 100% died after two days under 51°C+_1°G When the temperature was decreased to
48°C+J°C, shigella ova died within one day. Salmonella ova died within 3 days.

From the mesophilic experiments, it is reported that hookworm ova died in 10 days and 96.5%, 98.8%
and 99.1 % of ascaris ova died in 20,26 and 33 days respectively.

From Europe Scheffer et al. report that they found no confirmation of the claim that pathogenic typhus-
enteritis bacteria are destroyed during fermentation at 30°C. They however believe that anaerobic
digestion may be considered a more hygienic process than aerobic systems of manure processing. But the
30°C fermentation temperature requires a very long retention time to yield reasonably safer outputs
(cited by Van Brakel, 1980:106)

Thus it is clear that higher fermenting temperature can accelerate the fatality of ova and pathogen.
The alternative for lower temperature is longer HRT. In addition it is doubtful whether the Third
World small farmers can afford extra energy sources to heat the digester.

Feedstock combinations and survival time of schistosoma:

An experiment was conducted in China in which the feedstock used comprised of 5% human excreta,
90% animal excreta and 5% stalks. The data on survival time of schistosoma is presented below.
Table 69: Relation between feedstock concentration and the
survival time of schistosoma ova
Experiment 1
Season Summer Autumn
Digester temp. 19-23.5°C 24-24.5°C
Outcome Survival days Free ammonia(%) Survival days Free ammonia

Feed concentration (%) 90 It.5 0.15-0.17 13 0.11-0.11

60 12.5 0.09-1.10 18 0.10-1.11
40 15.0 0.05-0.07 20 0.07-0.08

Source: APRBRTC, 1986: 171

Experiment 2

Concentration of human excreta (%) 1 6 10 14 20

Survival days of schitosoma ova 21 15 15 7 7

Source: APRBRTC, 1986: 171

3
In China a temperature range of 16-60°C is considered as a thermophilic formentation. In practice 53°C is adopted as
thermophilic.
4
The temperature adopted for mesophilic fermentation is 32-37°C

65
These experiments indicate that higher feedstock concentration generate higher proportion of
free ammonia which then accelerate the death of schistosoma ova.

Treatment of residual sludge from the digester:

It was mentioned earlier that ascaris ova settle in the residual sludge at the bottom of digesters.
Disinfection of this residue was mentioned as a necessary step before applying in the Reid. It is
estimated that about 50% of live acaris ova may be found in this residue. Some of the treatment
methods developed in China and other places will be reviewed in the chapter on slurry treatment
and composting.

4.4 Sanitary regulations

In Europe and North America there are strict regulations pertaining to the utilisation/disposal
of slurry/sludge from biogas digesters involving seewage sludge and agricultural/human
wastes. China has also developed such regulations. In China ascarias is one of the major diseases.
Thus, the data on ascaris ova are commonly taken as the parasitological index. In areas where
schistosomiasis and hookworm disease occur in epidemic forms, the ova of these pathogens are
taken as reference index.

Bacteriological index based on Bacillus coil is developed. This index is used for the detection of
other enteropathogenic bacteria that have similar characteristics and that live in manures.

These indices are used to determine whether or not the following sanitary regulations are
followed:
• The retention time in digester must be 30 days,
• The reduction rate of parasitic ova must be 95% or more,
• No living ova of schistosome and hookworm should be found,
• The breeding of flies and mosquitoes should be effectively prevented,
• Scum and residue can be used as fertilizer only after disinfection,
• The fatality rate of the ascaris ova should be 95°-100
• In case compost is adopted in treating residue, the period of composting should
be for 5-7 days with temperature of 5O-55°C, etc. (APRBRTC, 1986:164;
ENFO, 1988:1)
4.5. Biogas slurry utilization and health and sanitary improvements:

The efforts in China have significantly contributed in the improvement of health and sanitation
in rural China by systematically utilizing scattered garbage, pieces of straw and stalks.

A case study in a village before biogas adoption reports that hookworm infection registered
63.8%. The average egg count was 500/gram of faeces and the soil was infected with
hookworm larvae. After biodigestion was adopted the hookworm infection declined to 4.07%
within few years. The egg count decreased to 50 egg/gram of faeces. Similar results have been
reported from other Chinese villages. Similar reduction is also reported in dysentery and
enteritis cases. Within a few years dysentery and enteritis cases reportedly decreased by
80-%. Reduction of fly density by as much as 80.1 % is reported from some areas where biogas
plants are adopted (ibid).

66
4.6. Sanitation and public health aspects of slurry utilization in Nepal

In Nepal systematic studies in terms of" before' 'after' scenerious in the context of public health
and sanitation have not been conducted. Some general reports have indicated the improvements
of l general hygienic conditions' since the attachment of toilets to biogas plants (Castro et al,
1994:22; East Consult, 1994:33; 1996:34-35 ). East ConsuIt (1994) has also reported
that all the plant owner respondents felt some reduction in odour due to toilet connection. In
the 1996 study, East Consult has reported: 'Contamination of water source and soil have been
reduced largely (JK). Diseases transmitted by water, air, dust and insects have also decreased
appreciably....'(1996:34):

General literature on biogas normally claims a reduction in odour of faeces and other manures.
From North America there comes a report that shows the application of anaerobic digestion in
odour reduction of swine manure. According to this report (Welsh et al., 1977:22-26)
anaerobic digestion at 35°C is more effective in reducing odour than anaerobic digestion at 25°C.

In Nepal, the Biogas Support Program (BSP) a biogas programme funded by the Netherlands
Development Organisation (SNV), commissioned laboratory analysis of slurry compost, sun-
dried slurry, fresh slurry, fresh slurry from toilet attached biogas plants (ATC, 1977). The
parasitical and bacteriological test of toilet attached slurry from nine districts showed the
presence of ova of three species of nematodes Ascaris lumbicoides, Trichuris trichuria (the
report is not specific about which of the two species, Nectar americanus and Ancylostoma
duodenaie, was present in the sample), one species of protozoa (Giardia lamblia) and one species
of bacteria (Salmonella typhi). It is useful here to briefly mention the diseases associated
with these organisms.

Ascaris lumbricoides:

Ascaris lumbricoides is a nematode worm that is distributed throughout the world. It is the
largest of the human intestinal worm. An adult female measures up to 35 cm in length. Eggs,
passed out in the stools may be transmitted to a host in contaminated food or drink. Larvae
hatch out in the intestine and then undergo complicated migration, via the hepatic portal vein,
liver, heart, lungs, windpipe, and pharynx, before returning to the intestine where they later
develop into adult worms. The disease caused by this nematode is known as ascariasis. Adult
worms in intestine can cause abdominal pain, vomiting, constipation, diarrhoea, appendicitis, and
peritonitis; in large numbers, they may cause obstruction of the intestine. The presence of
migrating larvae in the lungs can provoke pneumonia. Ascariasis occurs principally in areas of
poor sanitation.

Trichuris trichuria (Whipworm}

Whipworm is a small parasitic whip-like nematode worm that lives in the large intestine. Eggs are
passed out of the body with the faeces and human infection results from the consumption of
water or food contaminated with faecal material. The eggs hatch in the small intestine but
mature worms migrate to the large intestine. The diseased condition known as Trichuriasis occurs
principally in humid tropical regions. Symptoms include bloody diarrhoea, anaemia,
weakness, and abdominal pain. But these symptoms are evident only in heavy infestations.

67
Hookworm

Although the ATC analysis does not indicate which species was detected in the samples, it should
be noted that either of the two species Nector americanus and Ancyslostoma duodenale live as
parasites in the intestine of man, and cause Hookworm disease. Hookworm larvae live in the soil
and infect man by penetrating the skin. The worms travel to the large intestine and from there
pass via the windpipe and gullet to the small intestine. Heavy hookworm infestations may cause
considerable damage to the wall of the intestine, leading to a serious loss of blood; this in
conjunction with malnutrition, can provoke severe anaemia. Symptoms include abdominal pain,
diarrhoea, debility; and mental inertia. The disease occurs throughout the tropics and sub-tropics
and is prevalent in areas of poor personal hygiene and sanitation.

Giardia lamblia

Germs of parasitic pear shaped protozoa inhabiting the small intestine of man. Gardiasis or
lambliasis, the disease caused by this protozoa exhibits symptoms that include diarrhoea, nausea,
belly ache, and flatulence, as well as the passage of fatty stools. Man becomes infected by eating
food contaminated with cysts containing the parasite. The disease occurs throughout the world
and is particularly common in children.

Salmonella typhii

Salmonella is a genus of motile rodlike gram-negative bacteria that inhabit the intestines of anima!
and man and cause disease. Salmonella typhi causes typhoid fever. Other species cause various
other conditions. This was the only bacterial species found by the ACT analysts from the 50
samples from various parts of the country

The ATC analysis found the ova parasitic worms in only 16% of the sample (in 8 out of 50
samples). Except for Trichuris trichuria and Giardia lamblia the egg counts were very low.
The ATC report noted that the samples might have been collected during a period of lower
microbial activity. An analysis of samples collected during the summer, notes the report, would
have given a potentially different result of parasitic and bacterial presence.

Anyway, if the number and magnitude of parasitic and pathogenic presence in the toilet
connected slurries are accurately represented in the report, the consequences for health and
sanitation should not be so alarming. As shown in earlier part of the review in this chapter,
human excreta is attributed to numerous pathogenic organisms, the numbers of species generally
exceeding those found in animal manures. The lower number and magnitude of pathogenic
species present in the Nepali sample could be due to the lower human excreta to cattle manure
ratio in the digester input.

68
 CHAPTER 5

SLURRY TREATMENT

As the effect of different forms of slurry on crop production has been reviewed in Chapter 3, this
chapter will deal with different forms of slurry with special attention to slurry composting.

5.1. Fresh liquid bioslurry

It is evident that the- biogas plant slurry is mostly used as manure with some additional applications
as seed dressing agent and pesticide. Biogas slurry is also used in vermiculture and mushroom
production as well as feed for cattle and fish. To delve into these areas is out of the scope of the
present review.

By now it is evident that bioslurry in liquid from involves relatively minimal amount of nutrient loss.
But bioslurry cannot be applied to the field the moment it comes out of the digester because
efficiency can be obtained only when it is applied in phytophysiologically most advantageous times.
This is perhaps the most important limiting factor for fresh liquid slurry application. As was
reviewed in Chapter 3, fresh slurry has also the potential to cause eutrophication and toxic effects
(e.g. H2S, ammonia concentration) on crops. In addition, as the preceding chapter has shown,
concerns have also been expressed on the health and sanitation aspects of fresh liquid slurry,
especially fresh liquid slurry derived from human excreta (Kshirsagar, 1986). Even if pathogen
elimination in conjunction with the adoption of appropriate HRT is achieved, the application of fresh
liquid slurry is still problematic in view of the unavailability/unaffordability of mechanical systems
for fresh slurry application in South Asia. Even if application of slurry through irrigation channels is
often advocated, lack of sufficient gradient, irrigation sources and channels, etc., are often the
limiting factors.

Thus even if fresh liquid slurry is nutritionally superior, slurry researchers generally agree that
utilisation in this form is not always applicable. Furthermore, if the slurry is derived from human
excreta, fresh liquid application is even more problematic due to socio-cultural taboos associated
with human faeces, at least in parts of South Asia (Patel, 1986). In addition, as already seen, some
researchers are extremely cautious (Kshirsagar, 1986:37-43) about the health and sanitation aspects
of utilising fresh liquid slurry from biogas plants fed with human excreta.

Surveys among farmers in Nepal (Castro et a!., 1994: 21-22; East Consult 1994: 35: DevPart 1998:
36; Gajurel et al., 1994:12) reported that farmers felt that the liquid slurry was not convenient for
field application and that slurry was not always available at the time of field application. Another
study (New ERA, 1995:22) reported that only 18% of the respondents used slurry in semi-liquid
form. Only 4% of the respondents said that they used slurry after making compost.

A study in Nepal (New ERA, 1995:2) showed that 72 % of the farmers used slurry in dry form. A
later study by DevPart (1996:36) reported that 64% of the biogas adopters were using slurry in dried
form. A study by East Consult showed that 60% of the slurry users were using it in dried form.
These evidences indicate that wet slurry is indeed an inconvenient form for utilization in the farm
lands in underdeveloped countries like Nepal.

69
5.2. Treatment of fresh slurry.

Slurry researchers largely agree that liquid slurry has to be treated to make it easier for handling and
transportation; to enable it to be conveniently used according to the critical growth stages of crop
plants, and to eliminate whatever parasitic/pathogenic organisms are left in it after the digestion.
'Treatment' here has both chemical and physical dimensions. Some of the treatment, methods are as
follows:

5.2.1. Liquid slurry storage

Due to a multiplicity of reasons, slurry is not only dried it is also stored in liquid form. Generally,
immediate application is neither warranted nor possible. The possible range of options are many. If
nutrient conservation is one aspect, transportation and storage in large volumes are formidable for
ordinary farmers in the third world.

The collection tank can be a brickwork storage basins or, if the soils are suitably impermeable,
simple reinforced pits are constructed. Since complete liquid storage for extended storage periods
would necessitate high storage volumes, usually only part of the bioslurry generated can be stored in
this form. The size of the storage basin is determined by the amount of fertiliser needed at the time
of application. If liquid application is planned, storage capacity is usually planned for few weeks.
Storage basins with volumes ranging from 2 to 6m3 are generally recommended for small scale
plants. For a smaller plant this should be adequate for even drying and composting (Demont, etal.,
1991:29-30).

• Application of liquid slurry:

In areas with relatively mechanised farm operations, the contents of the storage tanks are thoroughly
agitated and filled into a liquidmanure spreader; or if the slurry is mobile enough, put through
irrigation sprinklers (GATE, 1996). If the storage system is properly conserved and is not exposed to
the sun little nitrogen is lost and this is the main advantage of liquid storage. On the other hand, as
mentioned earlier, liquid storage requires a large storage capacity entailing high initial capital
outlay. The practice of spreading liquid slurry also presents problems in that not only storage tanks
are needed, but transport vessels as well, and the amount of work involved depends, in part, on how
far the digested slurry has to be transported. For example, transporting one ton for a distance of 500
m in an oxcart takes about five hours (200 kg per trip). Distributing the dung over the field requires
another three hours (GATE, 1996). Similar studies with liquid slurry is lacking, but in any case,
handling and transportation of liquid slurry must be more difficult in the South Asian situation.
One of the advantages of liquid slurry is that it can be spread uniformly in the field. Slurry
researchers in India suggest that for basal dressing, bioslurry can be applied before sowing or
planting and easily worked into the soil during tillage operation. If the crops are sown or planted in
rows, bioslurry can be applied in furrows or seed holes (Demont et al., 1991:30). Careful covering of
bioslurry after application prevents nutrient losses and enhances crop yield. For fruit and other
perennial cultures, bioslurry should be applied around the plants and covered with mulch. Bioslurry
in such cultures is not worked in order not to disturb the root system. The mulch layer prevents the
bioslurry from drying out and promotes the absorption of nutrients by the plant. Bioslurry should be
applied regularly during the vegetation period in accordance with the plant nutrient requirements. It
is relatively easier to apply in the kitchen gardens due to their closer proximity to the biogas plants.
However, it has often been suggested that fresh liquid bioslurry, especially if it is derived from
human excreta, should be kept from coming into direct contact with harvested crops.

70
Fresh liquid bioslurry derived from human excreta is also not advised for application (top dressing)
in lettuce and vegetable crops {GATE, 1966, Kshirsagar, 1986).

5.2.2. Dehydration by sun drying

It is only possible to dry digested slurry as long as the rate of evaporation is substantially higher than
the rate of precipitation (GATE, 1996). The main advantage of drying is the resultant reduction in
volume (i.e. weight). Also it makes spreading possible. The cost of constructing a shallow earthen
drying basin is modest. It can even be dried on a stable surface near the plant overflow (Demons
1991). On the other hand, drying results in a near-total loss of inorganic nitrogen (up to 90% ,
corresponding to roughly 50% of the total nitrogen content (Demont et al, 1991; GATE, 1996).

Due to the excessive moisture content (over 90%) of the slurry, sun drying is one of the most widely
used slurry treatment practices in South Asia. It facilitates simple storage. Sun-dried slurry can be
transported and applied like dung. It is not necessary to devise new application modes or arrange
new transport equipment. In the drying process, the pits or beds are periodically filled with
bioslurry, which is removed once the desired moisture content is reached. The drying process
requires relatively large drying areas.

5.2.3. Filtration

In North America and Europe large sewage treatment plants and livestock operations use larger
filtration systems (Haywood, 1997: 55-57). In others, methods like coagulation using either
chemical, electrolytic or air flotation processes, or mechanical processes using vacuum drum filters,
hot year drying etc., are in use. However these are not practical systems as far as farmers in South
Asia are concerned. Filtration by employing sand, stones and leaf has been tried at few places but its
practicality is yet to be established (Dhussa, 1986:31).

It has been reported (Kate, 1991: 10-11) that ammonia loss during direct sun drying could be
reduced by using low grade apatite of single superphosphate.

In a process developed at IARI, the supernatant is removed from the top and the settled sludge is
removed from the bottom of the digester. Broken leaves, sawdust or charcoal dust are used as
absorbent and repeatedly soaked in the slurry. The drying process results into doubling the quantity
of manure compared to drying of slurry alone. A further improvement of this process was
accomplished at the Center of Science for Village (Wardha, India). The effluent slurry from the
outlet of biogas plant passes over the organic bed arranged in the filtration tank and the water liquid
flows out through an outlet placed at the far end and collects in a tank. Two such filtration tanks are
made to run alternately (Kate, 1988 in Kate, 1991:1 I). It is reported that about 20 to 30% of the
total water added to digester with cow dung is recovered and average moisture content of slurry is
brought down to about 30-35% after two weeks of drying (ibid).

As elsewhere, Lakshmanan (1988) from Annamalai University in South India reports the result of an
experiment involving gypsum, rock phosphate, calcium carbonate and burnt rice husk as absorbents.
Among these materials gypsum added to the wet slurry at 25% of the weight of the slurry reduced
the moisture content of the slurry by 30% (W/W) and reduced the loss of nitrogen by 1 7%. Kalia et
al. (1994:22-24) reports the results of an experiment on low cost filtration pit for dewatering biogass
plant slurry in the hills. The filtration materials used were 3-5 mm thick sticks of weeping wilow,
bamboo, mulberry and kaigrass; the soiled contents of the slurry were found to have increased by
87%, 71%, 73% and 66% respectively after using these filters as compared to 29% in the slurry
dried in conventional pit. The developed pit cost only Rs. 150 and provided easy way of dewatering
slurry for its transport and for using the filtered water for mixing the fresh feedstocks. Goswami et

71
al. (1996:23-26) reports on a simple low cost technology, involving the preparation of a straw-screen
on a stout iron netting with mature rice straw, fresh neem leaves, and green weeds-- an improvement
over the earlier IARI versions of dewatering technologies- from which they claim that 88% of the
added water was recovered and the reuse of the water resulted in higher gas output. The recovered
semi solid residue looked almost similar to fresh cow dung in its physical state for easy handling and
disposal.

It is evident that biogas slurry can be directly applied to the farm land or dewatered to provide
separate liquid fertiliser and solid residual product that can be composted or used as manure as such.
The other alternative, the one practiced by most farmers in Nepal, is to use organic materials to use
as moisture absorbents and use the resultant product directly as manure or for composting.

5.2.4. Centrifugation.

If the separation for high nitrogen content materials is required to be done dehydration and filtration
methods cannot be effectively employed. If nitrogen rich biogas effluent is intended to be used as
cattle feed centrifugation process should be employed to get moisture free solid without losing the
nutritive value (Dhussa, 1986:111). Again the affordability of a centrifugation system in poor
farming households is a problem.

5.2.5. Composting

Composting is the biodegradation of organic materials into a humus-like substance. Composting, as

practiced by man is one of the more ancient of the agricultural arts. Traditionally, composting
consisted of piling of readily putrescible materials such as garbage, nightsoil, animal manure and
agricultural wastes with straw and leaves, and periodically turning the material as decomposition
progressed. Composting remained more of an art than a science when Sir Albert Howard
systematised the procedure in India (Price, Undated:! 35).

The review of effects of different forms of bioslurry on crop yield in Chapter 3 revealed the
important nutritional role of composts on crop production. But the differences and similarities
between aerobic composts and anaerobic digestates on the one hand and aerobic composts and
composts prepared from anaerobic digestates (slurries/sludges from biogas plants) are far from being
clear. Biocycle - The Journal of Composting Science reports that the differences are not clear even
in North America. Journal contributor Riggle (1996:82) reports that even if anaerobic digestates
contain higher nitrogen (because it is not volatilised during the digestion process) than aerobic
composts, the need for a series of comparative trials is envisaged. The matter of systematic research
in slurry/sludge/residual sludge composting is still in a very
preliminary stage.
Nonetheless composted bioslurry is said to combine the advantages of both dried and liquid
substrates:

• Matured bioslurry compost can be stored easily in windrows or heaps, and covered with
large leaves (banana, coconut, etc.) or plastic foil to protect against rain or excessive
evaporation.
• A composted bioslurry has a moisture content of only about 45% to 60%; it can be easily
transported to the field in standard containers.

72
 • Losses of the plant nutrients available in the bioslurry are substantially minimized since
most plant nutrients are incorporated by the microorganisms which decompose
carbonaceous plant tissues.

• The use of different plant residues expands the number of plant nutrients in the final
substrate {Demontetal. 1991:31).

• Composting can kill most of the remaining pathogens not eliminated during the anaerobic
digestion process (see Khandelwal, 1986:105-109, APRBRTC, 1983:172-173; Ghosh
1986:146 among many others).Thus composting is also important from health and sanitation
point of view.

5.2.5.1. Composting methods

Composting literature reveals that composting in the West is a highly mechanized process (Fairfield-
Hardy Process, Mechanical Static Pile system, Silo-Counter Flow Aeration System, Rotating Drum
Digester, Briquette System, to name a few). It is fruitless to go into the details of these systems for
their lack of applicability in Nepal.

Modern composting is a biological process which operates under aerobic conditions. The process
depends on the growth and activities of a mixed population of bacteria and fungi contained in the
organic materials to be composted. When condition is favourable, the decomposition proceeds. Five
fundamental parameters (common to all processes) essential to the composting process must be at
optimum levels if aerobic/thermophilic composting is to proceed rapidly,, effectively and efficiently:

• Temperature: Composting involves both mesophilic and thermophilic temperature

ranges which affect biological activity. At temperature below 40° C, the rate of reaction
and efficiency of the process increases in proportion to increase in temperature. This is
the range in which the mesophilic bacteria are active. The composting biomass initiates
its activity at ambient temperatures, steadily builds heat as microorganisms begin to
multiply, and the biomass undergoes degradation. When the mesophilic threshold has
been achieved, the mass will remain at a plateau, then gradually rise in temperature until
it reaches the thermophilic range. This plateau exists due to the acclimatisation and
adaptation of organisms which are divided into mesophiles and thermophiles. As the
temperature rise above 55° C, the rate of decomposition decreases, and very little
activity takes place above 70° C (Price, Undated: 136).

• Aeration: Aeration determines whether the composting process is aerobic or anaerobic.

It also determines the rate of the process; high-rate composting involves high-rate
aeration, slow-rate composting involves slow-rate or minimal aeration (ibid: 137).
• Nutrient (Substrate) and Nutrient Balance: Generally the simpler the form in which
the substrate occurs, the more rapid the decomposition occurs. To maintain adequate
food for the microorganisms a balance of nutrients is required. The C:N ratio has been
identified as significant; the optimum range for nearly all systems is 20-
25:1 (Gray, 1971:22).

73
 • Moisture Content: The optimum moisture content of the sludge-bulking agent (carbon
carrier) mixture before decomposition has been found to be in the range of 50-60%
(ibid).

• pH Level A profile of the pH level in a compost biomass indicates a drop in the pH

from a level of pH 6-7 to pH 4-5 at the outset of biological activity in the mesophilic
range. As decomposition proceeds the biomass becomes more alkaline till it reaches a
stable level at around pH 8 (Epstein, 1977:5).

It has been generally accepted that biogas slurry is a good starter for composting. Experiments
conducted at the Indian Agricultural Research Institute, Delhi, have shown that the digested slurry
can be profitably used as a starter culture for composting other organic waste materials like leaves,
straw etc. and in obtaining three times the quantity of manure than otherwise {Kate, 1991:12). It has
been reported that only 10 litres of slurry is sufficient to compost 100 kg of agro-waste by employing
semi-aerobic method of composting (ibid). Laura and ldnani{1977) composted wheat straw and
sorghum fodder with digested slurry under anaerobic condition for 45 days and found that the
addition of slurry accelerated decomposition of wheat straw and sorghum fodder from 10 to 30% and
15 to 40 % respectively (cited in Kate, 1991:12). The literature in the Asian context reveals the
following major composting method using biogas slurry.

5.2.4.1 .a. Open Window or "Window' System

Before mixing the dried plant residues with liquid bioslurry a location and shallow should be
selected near the biogas plant.

• One pan of dried plant residues should be soaked in 5-7 parts of bioslurry. One compost
unit (a heap, pile or a windrow) should be set up in one day in order to guarantee the
initiation of biological activity. The heat will begin to generate after 40 to 96 hours (Demont
et al, 1991:32) (a bamboo or metal rod can be placed in the middle of the heap to see the
temperature build up. Bare hands can grip the rod at 60°C. Compost thermometers are
available but they are expensive for ordinary Nepali farmers). After several days the
microbial reactions will shift from mesophilic to thermophilic and the temperature will raise
up CD 7O°C This biotic heat kills pathogens and pathogenic ova (APRBRTC, 1983:172).
An experiment from China reports that within 4 days, the temperature of the compost heap
gradually increased from 31°C-32°C to 60°C, and when this temperature was maintained for
32 days ail ascaris ova died (ibid).

• In ordinary rural conditions, the dimension of a bioslurry compost heap should be around
Ixixl.5m (height) and should not exceed 2.5 m in width or 1.8 m in height (Demont et
al, 1991:32).
• The compost heap should be turned after 14 days. Turning of the pile permits cooling
(mesophiiic) and assists in aerating the pile so that the metabolism remains aerobic and the
moisture content adjusted to 60%. After several turns the temperature falls. The failure of
the compost to increase temperature is used as a means to determine that the compost has
been stabilised. Bioslurry compost with window method becomes ready for field application
after six to ten weeks (APRBRTC, 1983:172). (After 15 weeks according to Demont,
1991:33).

74
5.2.4.l.b. 'General composting' of bioslurry

The difference in this method is that the materials described above are directly piled on the ground
without ventilation. Even if the temperature is lower than the open window system, experiments in
China have shown that longer period of composting in this way can get rid of ascaris ova and other
pathogens and ova.

Experiments in China (APRBRTC, 1986:173-174) have shown that addition of ammonia water raise
the ammonia concentration in the compost. This ammonia permeates into the egg shell and shell
membrane of ova and bacteria and kill them. With the addition of ammonia water at a concentration
of 0.2%, schistosome cannot remain alive after six days. Addition of urea is also reported to perform
the same function. A 0-4% urea water is needed to kill hookworm ova. The Chinese researchers have
also reported that granular manure can be prepared by mixing the biogas slurry with 1.3% urea and
fine soil. A reduced water content in these granules kill ova of ascaris and hookworm (ibid).

5.2.4.1.c. Pit composting of bioslurry

One often recommended practice in India and Nepal is to dig 2 to 3 compost pits (the size usually
depending upon the capacity of the biogas plant) near the biogas plant. Slurry is allowed to flow over
plant materials till these materials are wet with slurry. The slurry is then covered with plant
materials. This process continues till the pit is filled. When the pit is filled -up completely it is
covered with dry plant materials and soil. The pit so covered is somewhat higher than the ground
surface. The pit is left in this condition for about a month. After this the materials in the pit are
turned to facilitate aeration. The pit is again covered by plant materials and soil. Second and third
tunings are done in an interval of about two weeks. Similar process is followed for other pit/s.

As was mentioned earlier biogas slurry is a good starter for compost making. Table 70 below shows
that it takes less time for bioslurry compost maturation as compared to FYM compost maturation
(both covered and uncovered). The 'Losses' (the report is not specific about what constitutes 'losses')
is lowest in the biogas slurry pit composting as compared to FYM composting (both covered and
uncovered). The highest loss is reported in FYM composting without cover.

Table 70: Comparison of FYM and biogas slurry pit composting

Type of Manure Time taken for Losses (%)
maturing (days)
FYM composting without cover 120-150 45

FYM composting with cover 90-100 20-25

Biogas digested slurry (Spread over 60-70 7-10

composting material)

Source: Myles, 1985: 27

In Nepal, Surveys have reported increasing trend of using pits for composting biogas slurry. A study
conducted by Gajurel et al. (1994:11-12) reported that 40% of the respondents used slurry for
composting. It is not sure whether ' composting' also meant the haphazard putting of manures and
household wastes together. Karki et al. (1996:16) report that before the launching of the slurry
extension pilot programme, there were very few compost pits. After the programme they found
compost pits with a total volume of 7494 m3. They also found that the number of compost pits per
biogas family averaged 1.4 and the size of the pits averaged 6.6 m3.

75
DevPart (1996:35-36) reports that in 90% of the cases observed, slurry from the digester was directly
led to compost pits. The farmers also reported to have told the researchers that if dry materials are
added to the pits in the ratio of 1:4 (slurry: dry materials on w/w basis) moisture is absorbed by the
dry materials.

Lack of time, labour and space seems to be some of constraining factors for pit slurry composting.
Table 71 presents data on various constraining factors for pit slurry composting.
Table 71: Constraints faced by farmers for slurry compost making
S.No Constraints Response
I Time 21
2 Labour 21
3 Space 13
4 Bedding materials 9
5 High water table 9
6 Diluted slurry 7
7 Wide distance from shed to pit 6
8 Negligence by farmers themselves 5
Source: Karki et al. 1996 :16
The perceived effects of bioslurry compost on crop production is largely theoretical as data for
comparing fresh liquid slurry, sun dried slurry, bioslurry compost and ordinary compost are hard to
find. As long as farmers' perceptions are concerned, studies in Nepal have shown that they usually
they do not think that bioslurry compost has increased crop yield even if they feel that bioslurry
compost was more potent (Britt et al, 1994: 42). From another study, Karki et al'. (1996:19)
reported that 40% of the farmers were not sure about the superiority of slurry compost over FYM
vis-a-vis crop yield (rice and potato). Table 72 below presents farmers feelings about the quality of
slurry compost.

Table 72: Quality of compost against FYM

S.No. Farmers' feeling Respondents Percentage
1 Superior to FYM 42 48
2 Inferior to FYM 1 1
3 Yet to see 35 40
4 No response 10 11
5 Total 88 100
Source: Karki et al. (1996: 19)

In terms of quality, the study found that around 24% of the farmers were not sure about whether or
not slurry compost was a good manure (as compared to 64% who thought that slurry was a good'
manure). Table 73 below presents farmers7 perceptions on the quality of slurry compost.

Table 73: Farmers' perceptions on the quality of slurry compost

S.No. Quality of compost Respondents Percentage
1 Good 56 64
2 Bad 2 2
3 Yet to see 21 24
4 No response 9 10
5 Total 33 100

Source: Karki et al., 1996:14)

76
It seems that the idea of superior manurial value of slurry compost (over FYM) is not a taken by all
the farmers. Demonstration programmes can be effective in these situations.

The composition of slurry compost varies according to the different plant residues used to produce it.
Table 74 presents data on the composition of slurry compost.

Table 74. General composition of slurry compost based on cattle dung based slurry
Constitution Percentage
Dry-substance 41-55
Organic carbon 56-77
Total nitrogen 0.6-1.0
Total phosphorous 0.5-0.8
Total potassium 0.6-1.5
Source: Demont et al. 1991

There have been no systematic comparative studies of the nutritive quality of slurry composts based
on slurries derived from different organic materials ( used as digester feedstocks). In addition,
research is also lacking in the quality of slurry compost prepared from different organic materials as
additive. One experiment from China reports on the effect of slurry compost prepared from
phosphorous (phosphohumate). Table 72 below presents data from this experiment.

Table 75: Effect of biogas phospo-humate on major crops

Rice (2)* Wheat (13)* Sweet potato (3)* Rape (5)*

Treatment Yield increase Yield increase Yield increase Yield increase
jin/mu jin/mu % jin/mu jin/mu I % jin/mu jin/mu % jin/mu jin/mu %
1. Check 581.5 ----- — 528.6 ..... .... 2772 ........ ... 246.0 —- ...
2. Phosphorite 620.0 38.5 6.6 558.6 60.0 1 1.4 2959 !87 6.7 246.0 0 0
powder 40-50
jin/mu
3. Digester 634.3 52.8 9.1 581.4 72.8 13.8 3250 478 17.6 260.2 14.2 5.8
sludge 400-
1000 iin/mu
4. Bio-gas 653.3 71.8 1.3 611.7 83.1 15.7 3302 530 19.1 258.0 22.0 8.9
phosphohumate
Note: * The numbers in parenthesis indicate the number of experiments
Source: APRBTC, 1983:158 1 jin = .5 kg; l mu = 0.667ha

Table 75 shows increased yield in wheat, sweet potato and rape with the application of phospho-
humate. in the case of rice, digester sludge gave higher yield than phospho-humate. Higher moisture
requirement for rice may be the reason.

5.2.5. Pathogen reduction by bioslurry composting

The assertions of majority of the slurry researchers have been that with composting the further
reduction of pathogens/parasitic ova will take place. Thus bioslurry compost is taken as a product
which has higher manurial value and which is safer, from health and sanitary aspects, for field
application. Table 76 below provides data on pathogen elimination in aerobic digestion and
composting.

77
 Table 76. Pathogen elimination and survivability in unheated anaerobic digestion and
composting

Organism In-unheated anaerobic digestion In composing

1, Enteric May survive for over three months Killed rapidly at 60°C

2. Salmonellae May survive for several weeks Killed in 20 hrs at 60°C

3. Shigellae Unlikely to survive for more than Killed in hr. At 55°c or in 10 dys at
a few days 40°c
4. E-Coil May survive for several weeks Killed rapidly killed above 60°C
5. Cholera May survive for one or two weeks Killed rapidly 55°C
6. Leptospire Survive for not more than two days Killed in 10 mts. At 50°C
7. Entamoebacysts May survive for three weeks Killed in 5 mts at 50°C and i day at
4O°C
8. Hookworm ova Ova will survive Killed in 5 mts at 50°C in 20 hrs. At
SO°C and 200 hrs 45°C
9. Ascaris ova Ova will survive for many moths Killed in 2 hrs. At 55°C in 20 hrs.
At 50°C and 200 hrs 45°C
10. Schistosome Ova may survive for many months Killed in 1 hr 50°C
11. Taenia ova Ova will survive for a few months. Killed in 10 mts. Ai 58°C and in
over 4 hrs at 45°C
Source: Navrekar, 1986:57 mts-minutes: hrs-hours

The above table shows that with appropriate retention time composting helps the elimination of
many pathogens and parasitic ova. Composting of bioslurry thus contributes in the public health
as well as better crop yield.

78
 Bibliography

Acharya, C.N., 1961. Preparation of Fuel Gas and Manure by Anaerobic Fermentation of Organic
Materials. New Delhi: Indian Agriculture Research institute.

Acharya, C.N., 1953. 'Cow Dung Gas Plants.' Indian Fmg. N.S. 2 (9): 16-18; Acharya, C.N., 1952.
'Organic Manures.' I.C.A.R. Res. Rev. Ser. Bull. 2. New Delhi.

Adhikari, Poorna K., 1996. Effects of Biogas Plants on Family Health, Sanitation and Nutrition ( A
Case Study in Lamjung District). Kathmandu: BSP, SNV-Nepal.

Asia-Pacific Regional Biogas Research-Training Centre (APRBRTC), 1983. Biogas Technology:

UNDP-ESCAP-FAQ-CH1NA Biogas Training Course. Chendu, China.

ATC, 1997. Report of Laboratory Analysis of Manure Samples. Kathmandu: ATC

Berry, Walden. 1976. 'Where Cities and Farms Come Together'. In Merrill (ed.) Radical Agriculture,
Mew York: Harper and Row
Berry, Walden. 1977. "The Agricultural Crisis as a Crisis of Culture'. In Gordon Douglass (ed.)
1984. Agricultural Sustainability in a Changing World Order. Boulder, Colorado: West view
Press

Bhatta, A.P., A.K. Shukla and P.K. Dangi, undated. Performance of Bio-gas Plants in Mangalpur
and Sharadan3gar Village Development Committees in Chitwan. Rampur,Nepal: 1ASS

Bhattarai, Mukunda P., 1990. Study Report for Detailed Biogas Potential in Dhading District.
Kathmandu: Dhading Development Project.

Bhattarai, S., 1987. ' Report on the Observations on Effect of Effluent of Bobar Gas Plant on the
Yield of Wheat Under Irrigated and Rainfed Condition.' Contribution from Sol Science and
Agriculture Chemistry Division for the Winter Crop Seminar, Aug. 14-17, 1978).
Kathmandu: Division of Soil Science and Agricultural Chemistry

Bhattarai, S. and S.L. Maskey, 1988. 'Effect of Azotobactor Inoculation in Combination with
Different Sources of Organic Manures .' Proceedings of National Conference on Science and
Technology, April 24-29, 1988, pp 81-85. Khumaltar, Kathmandu: Division of Soil Science
and Agricultural Chemistry

BMZf GTZ, BOARDA, Ministry of Energy, DNES, and UNDARP, 1990. International Conference
on Biogas-Technologies and Implementation Strategies (Report) Pune, India.

Britt, Charla, 1994. The Effects of Biogas on Women's Workloads in Nepal: An Overview of
Studies Conducted for the Biogas Support Program Kathmandu: BSP.

Britt, Charla, 1994. The Effect of Biogas on Women's Workloads in Nepal: An Overview of Studies
Conducted for the Biogas Support Programme. Kathmandu: BSP.

79
Bulmer, A., John Finley, David Fulford, and Namie M. Lau-Wong.1985. Biogas-- Challenges and
Experience from Nepal Vol. 1,11 Kathmandu, Nepal: Mnited Mission to Nepal.

Campino, 1990. The Effect of Nitrogen from Liquid Manure, Bioslurry and Urea on Hay and
Maize in Tropical Columbia.' In Biogas Forum, Vol 1 special.

Chanakya, H.N., 1986. 'Nighsoil Biogas Plants: Health Aspects and Design.' In Biogas from
Human Waste. (Workshop Report) New Delhi: CORT.

Chawla O.P., 1984. ' Manurial Aspects.' Advances in Biogas Technology. New Delhi: ICAR.

Consolidated Management Service Nepal (P). Ltd., 1996. District Level Training Manual on Biogas
Technology. Nepai: FAO/TCP.

Consortium on Rural Technology {CORT) , 1993. Biogas Slurry Utilisation. (Seminar Report) New
Delhi: CORT.

Consortium on Rural Technology (CORT) , 1986. Biogas from Human Waste. (Workshop Report)
New Delhi: CORT.

Cott, A.M, 1974. ' Anaerobically Digested Pig Slurry as Resource for Crop Production.' Anaerobic
Digesiion MIRCEN, Vol. No. 1, 1984 page 85-86.

Daize, Hu, Meng Xun, Yang Kejun and Ren Shengquing, 1991. 'Bio-Digestion - the Pivot of China's
Eco-agricultural Construction.' In Biogas Forum Vol. II, No. 45, 1991.

Dayal, M. 1986. ' Keynote Address,. In Biogas from Human Waste. (Workshop held in Delhi) Delhi:
Consortium on Rural Technology.

de Castro, J.F.M., A.K. Dhussa, J.H.M. Opdam and B.B. SNwal. 1994. Mid-Term Evaluation of the
Biogas Support Program. Kathmandu: Dutch Directorate for International Cooperation

Demont, D., A. Sckeyde, and A. Ulrich, 1990. ' Possible Applications of Bioslurry for the Purposes
of Fertilisation.' In Biogas Forum , Vol. 1 Special.

Department of Science and Technology, Govt. Of India, 1981. Biogas Technology and Utilization:
A Status Report. New Delhi: DST.

Demont, D., A. Sckeyde, and A. Uirich, 1991. ' Possible Applications of Bioslurry for the Purposes
of Fertilisation.' In Changing Villages, Vol. 10, No.l, ]an-Mar., 1991.

Demant, Dierk. 1990. ' Biomanure from Small Biogas Plants'. In gate 2/90

Demuynck et al, 1984. Biogas Plants in Europe: A practical Handbook (Solar Energy R and D in the
European Community) Series e, Volume 6 (Energy from Biomass). Dordrech, Holland: D.
Reidel Publishing Company (for the Commission of the European Community).

Desai, S.V. and S.C. Biswa, 1945. 'Manure and Gas Production by Anaerobic Fermentation of
Organic Wastes.' Indian Fmg. 6:67-78.

Desai, S.V. and S.C Biswas, 1964. 'Combustible Gas from Cow Dung.' Indian Fmg. July, 1946:140-
43.

80
DevPart - Nepal, 1996. Final Report of Impacts of Biogas on Users. Kathmandu: BSP.

Dhussa, A.K., 1985. ' Biogas Plant Effluent Handling and Utilisation.' in Changing Villages Vol.7,
No.l.

Dhussa, A.K., Raymond Myies, and Nasae Canada Lmisae, 1985. 'Design and Implementation of a
Pilot Demonstration Community Night Soil Biogas Scheme.' in Changing Villages Vol.7,
No.5.

Dhussa, A. 1986. 'Nightsoil based biogas plants'. In Biogas from Human Waste. CORT: Delhi

Dhussa, A. 1986.' Biogas plants effluent handling and utilization'. In Biogas from Human Waste.
CORT: Delhi

Droogers, P. And }. Bouma, 1996. ' Biodynamic vs. Conventional Farming Effects on Soil Structure
Expressed by Simulated Potential Productivity.' in Soil Science Society of America Journal
Vol. 60 No. 5.

EastConsuIt (P) Ltd., 1994. Final Report BSP Biogas Users Survey -1992/93. Kathmandu: Biogas
Support Programme, ADB/N, SNV-Nepal, GGC.

EastConsuIt (P) Ltd., 1996. Biogas Users Survey 1994-1995. Final Report Biogas Support
Programme (A Joint Programme of Recognized Biogas Companies, ADB/N, RBB, NBL and
SNV-Nepal. Kathmandu: BSP.

Ef-Halwagi, M.M., 1980. ' The Development and Application of Biogas Technology in Rural Areas
of Egypt. National Research Center, Egypt: Applied Science and Technology Project No.
263-0016.

ENFO, 1988. Chinese Biogas Digesters.' In Environmental Sanitation Information Center. Bangkok:
AIT.

Fair, G.M., 1934. * Digestion of Garbage.' Journal of Sewage Works. 6:259-61.

Farrinton, J. and Adrienne Martin. 1990. Fanner Participation in Agricultural Research: A Review of
Concepts and Practices. Agricultural Administration Unit Occasional Paper 9, London:
Overseas Development Institute

FAO, 1975. Organic Materials as Fertilizers (Report of an expert consultation held in Rome, 2-6
December 1974). Rome: FAO.

Fowler, G. J and G. W. ]oshi,1923. "Studies on the Fermentation of cellulose.' Journal of Indian

institute of Science, Banglore 3:39.

Frossard, E., S. Sinaj, L-M Zhang, and JX. Morel, 1996. "The Fate of Sludge Phosphorus in Soil-
Plant Systems.' In Soil Science Society of America Journal, Vol. 60, No. 4, 1996.

Fulford, D.J. 1978, Biogas in Nepal -- The State of the Art. Butwal, Nepal: UMN

Gajurel, Om. P., Wim J. van Nes, and Basudev Neupane, 1994. Survey 1990-91 on GGC Biogas
Plants. Butwal: Gobar Gas Company Research Unit, Nepal.

Garde, R.V., D.R. Ranade and S.H. Godboie, 1985. 'A Note on Survival of Saimonellas during
Anaerobic Digestion of Cattle Dung.' In Biogas Forum No. 29.

81
Gaur, A.C. and K.C Dhandelwal, 1986. "Manure from Anaerobic Treatment of Human Waste/ In
Biogas from Human Waste (Workshop Report). New Delhi: CORT.

gate, 1996. ' Sludge ~ Management'" .In Internet Website htt://www.gtz.de/gate/isat/at-

info/biogas/appldev/sl udge.html

Geoffrey, Barnard, 1985. Agricultural Residues as Fuel in the Third World. Earth Scan: International
Institute for Environment and Development, The Beijer Institute, The Royal Swedish
Academy of Sciences, Energy Information Program. Tech. Report No. 4. London: IIED.

Gerretsen, F.C. and H.de Hoop, 1957. 'Nitrogen Losses during Nitrification lb Solutions and in Acid
Sandy Soils, in Can. J. Microbiol, 31, pp. 359-80. 1957.

Ghosh, S.I986. Prologue'. In Biogas from Human Waste. CORT: Delhi

Goswami, K.P., P.S. Bhorania and K.P. Patel, 1996. ' Recovery of Water and Manure From Biogas
Plant Slurry.' In Changing Villages, Vol. 15, Jan-June

Gnanamani , A. And R. Kasturi Bai, 1993. 'Carbon and Nitrogen Transformation of Biodigested
Slurry.' In Biogas Slurry Utilsation. New DeIhi:CORT.

Gupta, D.R., 1991. 'Bio-Fertilizer from Biogas Plants/ In Changing Villages, Vol. 10, No.l. Jan-
Mar., 1991.

Gupta, D.R., 1986. x Biogas from Human Waste: Public Health and Social Aspects.' In Biogas from
Human Waste (Workshop Report). New Delhi: CORT.

Gurung, Jit B. 1997. Evaluation of Farmer Participatory Action Research in Bhumlichwok VDC,
Gorkha. (Report prepared for GDP/GTZ Nepal). Kathmandu: Deva Pvt Ltd.

Gutterer, Bernd and Ludwig Sasse, 1993. ' Summary and Recommendations/ Report Biogas Survey
1992: Cross Section Analysis of Biogas Dissemination Programmes. Bremen, FRG:
BORDA (Bremen Oversees Research and Development).

Haywood, Frank, 1997. ' Handling Liquids and Solids on Hog Farms.' In BioCycIe Vol. 9, March.

HMG/ Nepal and SNV-Nepal, 1996. Proposal: Biogas Support Programme Phase III. Kathmandu:
BSP. Nepal.

House, D., 1978. The Compleat (sic) Biogas Handbook, Aurora: VAH1D, CR7002, USA.

Innotti, E.L., J.H Porter, ]. R. Fisher and D.M. Siever, 1979. 'Changes in Swine Manure Anaerobic
Digestion/ In Development. Ind. Microbiol., 20:519-529.

Institute of Soil and Fertilizer, 1979. 'The Utilization of Research Work on Digester Sludge and
Effluent as Fertilizer/ in Biogas Technology and Utilization- Chengdu Seminar, Sichuan
Provincial Office of Bio-Gas Development.

Isman, M., 1950. ' line etude sur les modes d'utilization pratique des appareils a gaz de fumier.
Elevage of Cult. 21, October, 1950.

]arvis, S.C., 1996. "Future Trends in Nitrogen Research.' In International Journal on Plant and Soil
Relationship 181:196. Dordrech: Kluwer Academic Publishers, Netherlands.

82
Jianmin, Fan, Liu Changix and Cao Shangxue, 1992. 'Effect on the Production and Quality of Beileil
Tobacco by Applying Biogas Fertilizer.' In Biogas Forum Vol (2) special. [Excerpted from
China Biogas, 1991, 9 (3), 34-35, translated by Ren Shengquing.

Jiashi, Sun and Zhu Reng, 1991. 'A Study on Applying "Biogas Fertilizer" to Prevent Plant Disease
and Insect Pests.' In Biogas Forum, Vol. 11 Special. [Excerpted from China Biogas, 8(4), 31
-33, 1990, translated by Ren Shengquing]

Joshi,N.V., 1945. Pres. Add. Agric. Sec, Proc. Indian Sci. Congr. Nagpur, 32 (2):219-21.

Kalia, Anjan K. And S.S. Kanwar, 1994. 'Filtration Pit for Dewatering Biogas Plant Slurry in Hills.'
In Biogas Forum, Vol. I, No. 56.

Kanthaswamy, V., 1993. ' Effect of Bio-Digested Slurry in Rice.' In Biogas Slurry Utilsation. New
Deihi:CORT.

Kanwar, S.S., Harsh Nayyar, D.P. Walia, 1993. Influence of Biogas Slurry on Germination and
Early Seedling Growth of Bread Wheat.' In Biogas Forum, Vol. Ill, No. 54.

Karki, Krishna B. And Bhimsen Gurung, 1996. Evaluation of Biogas Slurry Extension Pilot
Programme. Kathmandu: BSP, SNV-Nepal.

Kate, Tarak, 1991. 'Utilization of Anaerobically Digested Biogas Effluent Slurry or Sludge.' In
Changing Villages Vol. 10, No. 1 Jan-Mar., 1991.

Keizer, Cecilia, 1966. Effect of Biogas on the Workload of Women in Nuwakot District in Nepal.
Kathmandu: SNV-Nepal.

Keefer, C.E. and H. Kartz, Jr., 1 934. * The Digestion of Garbage with Sewage Sludge.' Journal of
Sewage Works, 6: 14-23, 250-25.

Ketkar, CM. , 1993. Use of Biogas Slurry in Agriculture.' In Biogas Slurry Utilsation. New
DelhkCORT.

Keyun, Deng and Choi Yunchu, 1990. "China Actively Promotes the Development of Biogas
Technology." In International Conference o Biogas: Technologies and Implementation
Strategies ( Conference Report, Pune India: a Joint Initiative of FRG and Republic of India,
Jan. 10th to 15th, 1990).

Khandeiwal, K. C. and S. S. Mahdi, 1986. Boigas Technology: A Practical Handbook Vol. I. New
Delhi: Tata McGraw.

Khandelwal, K.C., 1981. 'Promotion of Biogas System: Problems and Prospects.7 Seminar Com
Workshop on Janata Biogas Technology and Fodder Production. Karnal: NARI.

Kijne, Eric, 1984. Biogas in Asia Ultrecht, Holland: CDP (Consultants for Management of
Development bv).

Kogblevi, A., 1987. "Biodigester Effluent Boosts Up Vegetable Production in Benin.' In Biogas
Newsletter No. 25, November, 1987. [Excerpted from Directeur du Centre National
d'Agropedologie, B.P. 988, Cotonou, BENIN, July 1985).

Kololgi,S.D., S.S. Nagalikar and L.V. Hirevendkanagoudar, 1993. ' Effect of Biogas Slurry in Crop
Yield/ In Biogas Slurry Utilsation. New DeIhi:CORT.

83
Kone, Siaka, 1991. ' Contamination of Bioslurry.' In Biogas Forum Vol. IV. No. 47.

Kshirsagar, S.R., 1986. ' Nightsoil Biogas Plants: Health Aspects.' In Biogas from Human Waste
(Workshop Report). New Delhi: CORT

Kuppuswamy, G., A.R. Lakshmanan and A. Jeyabal, 1993. "Effect of Biogas Slurry on Rice-
Blackgram Cropping System.' In Biogas Slurry Utilisation. New DeihhCORT.

Latif, Ch. Magda Yassien abd el, 1990. Implementation Strategies and Biogas Technologies
Applied in Egypt.' In International Conference on Biogas. Jan. 10-15, 1990. Pune, India

Laura, R.D. and I.Idnani. 1972. "Effect on wheat yield and nitrogen uptake from manures made from
manures made from spent slurry'. In Plant Soil.32:283-295

Laurie, J.P., 194]. Methane-its Production and Utilization. London: Chapmann and Hall.

Lakshmanan, A.R.,1988.1 A report communicated at the R ST. D review meeting organized by the
DNES, Banglore

Lakshmanan, A.R., G. Kuppuswamy and A.Jeyabal. 1989.' Seed coating with biogas slurry and bio
fertilizers on blackgram'. In Microbiological Abstracts (31st Annual Conference of
Microbiologists of India, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. p.
106-107)

Laxamanan, A.R., G. Kuppuswamy and A. Jeyabal, 1993. I Use of Biogas Effluents as Seed Coating
Media for Successful Crop Production/ In Biogas Slurry Utilsation. New DeihhCORT.

LI, N.G., 1982. Is the Xinbu System Economically Feasible? Unpublished Manuscript.

Madan, Savitri, 1986. 'Nightsoil Based Biogas Plant: Its Role in Social Equality and Community
Benefits and the Problems of its Social Acceptance.' In Biogas from Human Waste
(Workshop Report). New Delhi: CORT.

Mahapatra, Krishna, 1985. 'The Puri Nightsoil Biogas Plant: A Sociological Evaluation Through A
Case Study.' in Changing Villages Vol. 7 No.6, Nov-Dec.

Mapuskar, S.V., 1991. Acceptance of Biogas from Human Nightsoil/ In Changing Village Vol. 10,
No. 3.

Mapuskar, S.V., 1986. 'Nightsoil Based Biogas Plants: A Useful Device for Rural Health and
Development. In Biogas from Human Waste (Workshop Report). New Delhi: CORT.

Maramba, Felix D., 1978. Biogas and Waste Recycling: The Philippine Experience. Manila: Maya
Flour Division, Liberty Flower Mills.

Martin-Leake, H. And LE. Howard, 1952 (a). Methane Gas from Farmyard Manure. Albert Howard
Foundation of Organic Husbandry (England): Publ.No.9.

Maskey, S.L, undated. Manurial Value of Biogas Slurry: Some Observations. (Paper presented at
International Workshop on Microbiologial aspects of Biogas production. May 31-
June3,Kathmandu).

84
Mohan, S. And M. Gopalan, 1994. % Biogas from Cow-dung for Insect Control During Storage/ In
Biogas Forum (1994) Vol II, No. 57. [Excerpted from Bioresource Technology, Vol. 39, No.
3, 1992, pp. 229-232.].

Moulik, T.K., 1990. 'Diffusion of Biogas Technology: Strategies and Policies.' In GATE 11, 15-3-6.

Myles, R.M., Rajen Sundaresan and T.C. Sharma, 1993. ' Biogas Slurry Experiment.' In Biogas
Slurry Utilsation. New Delhi:CORT.

Myles, R.M., 1985. ' Strategy for Promotion of Biogas Plants from Human Waste in Rural Areas.' in
Biogas from Human Waste (Workshop Report). New Delhi: CORT

Myles, R.M., 1985. A Practical Guide to Janata Biogas Plant Technology. New Delhi: AFPRO,
India.

Navarro, J. Diaz, 1984. ' Slurry as Bio-fertilizer.' In Biogas Forum No. 16, 1984.

Navrekar, S.M., 1986. ' Biogas From Nightsoil: The Health Aspect and Design.' In Biogas from
Human Waste (Workshop Report). New Delhi: CORT.

Nayyar, Harsh, S.S. Kanwar and D.P. Walia, 1993. ' Effect of Biogas Slurry as Seed Dressing Agent
on Seed Performance of Maize and Rice.' In Biogas Forum Vol. !V No. 55.

Neelakantan, S., 1981. ' Chemical Composition of Cattle Excreta and Its Manurial Value/ Seminar
Com Workshop on Janata Biogas Technology and Fodder Production. Karnal: NAR1.

Neelakantan, S., 1981. "Principles and Application of Anaerobic Fermentation and Biogas
Production. Seminar Com Workshop on Janata Biogas Technology and Fodder Production.
Karnal: NDRI.

New ERA, 1995. Survey of Users of Biogas Plants in Nepal. Kathmandu: BSP. New ERA, 1985.
Biogas Plants in Nepal An Evaluative Study. Kathmandu: Unicef.

Parikh, Rahul, 1989. ' Garbage Gas Manure Plant.' In Changing Villages Vol. 8, No.4, Oct.-Nov,
1989.

Parikh Jyoti K. And Parikh Kirit S., 1976. "Mobilization and Impacts of Bio-gas Technologies/ In
Energy (The International Journal) Voi.2., No. Great Britain: Pergamon Press.

Patel, Ishwarbhai, 1986. 'Social Aspects of Nightsoil Biogas/ In Biogas from Human Waste
(Workshop Report). New Delhi: CORT.

Patel, J.J., 1951. 'Digestion of Waste Organic Matter by Production of Methane and Organic
Fertilizer and a New Economic Apparatus for Small Scale Digestion (Gram Laxmi)/ Poona
Agriculture College. Mag. 42 (3): 150-59.

Myles, Raymond, 1982. Biogas Technology. New Delhi: Action for Food Production

Riggle, David, 1997. ' Anaerobic Digestion Gets New Life on Farms/ In BioCycle, January, 1997.

Riggle, David, 1996. "Anaerobic Digestion for MSW and Industrial Wastewater.' In BioCycle,
November, 1996 .

85
Rajagopal, R. and N. Chitra, 1992. 'Environmental Impacts of Bio-energy/ In Energy Environment
Monitor Vol. 8, No. 1, 1992.

Robin, Gregory and Juliana Hinterberger, 1990. ' Biogas Unit Slurry as a Fertilizer: The Experience
in Donimica.' In Biogas Forum, Vol. Ill, No. 42., 1990.

Rosenberg, G.7 1952 (a). Methane Production from Farm Wastes as Source of Tractor Fuel.' Journal
of Min. Agric. (England) 58: 487-94.

Sankaran, K.; G.V. Kothandaraman, and T.S. Manickam. 1981. ' Comparative study of biodigested
slurry as source of organic plant nutrient'. Coimbtore ; Tamilnadu Agricultural University
(Presented in a seminar in microbiology of biogas fermentation).

Sankaran, K and K. R. Swaminathan.1988. Residual impact of biodigested slurry as source of

organic manure'. In Management and Utilization of Slurry. Himansulu Publications

Santosh, Y.S. Satya, R. S. Arya and P. Vasudevan, 1993. ' Biogas Slurry-Production and Utilization
in Agriculture.' In Biogas Slurry Utilsation. New DelhhCORT.

Sathianathan, M.A. 1975. Achievement and Challenges. New Delhi: Association of Voluntary
Associations.

Schulz, Heinz, Dr., 1990. 'Agriculture Biogas Plants and the Use of Slurry as Fertilizer in the Federal
Republic of Germany/ International Conference on Biogas Technologies and
Implementation Strategies Report. January 10-15, 1990, Pune, India.

Scott, J.M.,1989. 'Seed coatings and treatments and their effects on plant establishment'. In
Advances in Agronomy, 42-43-83.

Schreeg, Thomas M. And D. Lyle Jarrett, III, 1996. 'Biosolids Cut Fertilizer Costs by $200 an Acre/
In Biocycle, October 1996

Shen, R.Z. 1985." The utilization of biogas digester in China'. In 'Aerobic Digestion, 1985'
(Proceeding of the 4th International Symposium on Anaerobic Digestion. Ghogzhou,
China).

Shen, R.Z. et. al. 1988. Study on the application of AFP and AES with anaerobically fermented
residues to prevent Barley Yellow Mosaic Virus'. In 'Anaerobic Digestion, 1988' Tilohe and
A. Rozzi (eds.). (Proceedings of the 5th International Symposium on Anaerobic Digestion,
Bologne, Italy).

Shiva, Vandana. 1988. The Violence of the Green Revolution: Ecological Degradation and Political
Conflict in Punjab. London Zed Books

Sindhu, B.S. and V. Beri, 1989. 'Effect of Crop Residue Management on the Yields of Different
Crops and on Soil Properties.' In Biological Wastes 27 (1989). England: Elsevier Science
Publisher.

Singh, ]. B. 1989. ' Biogas Slurry Manure/ In Changing Villages Vol. 8, No. 3, (Aug, 1989). Singh,
]. B.I990 ' Biogas Slurry Manure/ In Changing Villages Vol. 9, No. 3, (]uly-Aug) 1990.
Singh,]. B. ' Biogas Slurry Manure/ In Changing Villages Vol. 10,No.l (Jan.-Mar.), 1991.

86
Singh, Harpal, 1995. ' Indian Advances in Biogas Technology- Review of Work Done under A1CRP
On RES.' In Biogas Forum Vol. I, No. 60, 1995.

Singh, Shiv. P., H.N. Verma, D.K, Vatsa and A.K. Kalia, 1995. ' Effect of Biogas Digested Slurry on
Pea, Okra, Soybean and Maize/ In Biogas Forum Vol. IV, No.63, 1995.

Singh, Y . 1986. 'Health Aspects of Anaerobic Digestion'. In Biogas from Human Waste Delhi:
CORT

New ERA. 1995. Survey of Users of Biogas Plants in Nepal. Kathmandu: BSP

Tarn, D.M. and N.C. Thanh, 1983. ' Biogas Technology in Asia: The Perspectives/ In Renewable
Energy Review Journal Vol. 5, No.l, April 1983. Bangkok: Asian Institute of Technology.

Tentscher, W., 1985. 'Digested Effluent as Fertilizer'. Anaerobic Digestion, M1RCEN, Vol 3, No. 2,
1986, Page 136.

Theilen, Udo, 1990. ' Biogas-An Appropriate Technology or Third World Countries/ In GATE, 1 1-
15-3-6.

Thysen and Bunker, 1927. Microbiology of Cellulose, Hemicelluloses, Pectins and Gums. London:
Oxford University Press.

Tripathi, A.K., 1993. Biogas Slurry - A Boon for Agriculture Crops/ In Biogas Slurry Utilisation.
New Delhi:CORT.

UMN/Nepal, 1985. Biogas-- Challenges And Experience From Nepal Vol. I. Kathmandu: UMN.

UMN/Nepal. 1985. Biogas-- Challenges and Experience from Nepal Vol. 1,11 Kathmandu, Nepal.

Vaidya, A.K. and K.D. Joshi, 1996. 'Animal Housing Improvement Programme and Biogas Plants:
A Users' Assessment.' LARC Working Paper No. 96/40.

van Brake!, ]., 1980. The Ignis Fatuus of Biogas. Small Scale Anaerobic digesters ("biogas plants"):
a critical review of the pre-1970 literature Delft, the Netherlands. Delft University Press.

van Nes, Wim ]., 1996. ' Biogas Support Programme: Results in the Period July 1992-1995. In
Biogas and Natural Resource Manangement (BNRM) Nepal No. 51, April 1996.

van Nes. Wim ]. Undated. - proper use of Slurry' Kathmandu: BSP

Vargas, A.M., 1986. 'Regulation of Vegetation Growth Through Biogas Effluent/ Biogas Newsletter,
No. 23, November 1986.

Verma, O.S., 1981. ' Operational System of Govar Gas in Rural India/ Seminar Com Workshop on
Janata Biogas Technology and Fodder Production. Kamal: NARI.

Verma, O.S., 1981. ' Profitability of Biogas Plant.' Seminar Com Workshop on ]anata Biogas
Technology and Fodder Production. Karnal: NARI.

Vogtmann, H. And J.M. Besson, 1979. ' European Composting Methods: Treatment and Use of
Farm Yard Manure and Slurry/ Compost Sci./Land Uttil., 19(1): 15-19.

87
Waksman, S.A, 1932. Principles of Soil Microbiology, 2nd ED. Baltimore: Williams and Wilkings
Co. Inc.

Welsh, F.W., D.D. Schulte, E.J. Kroeker, and H.M. Lapp, 1977. The Effect of Anaerobic Aaerobic
Digestion upon Swine Manure Odors.' in Canadian Agricultural Engineering, Vol. 19, N0.2,
December.

WECS.1974. Energy Synopsis Report Nepal 1992/93. Perspective Energy Plan, Supporting
Document No.1 Report No.4/4/270494/1 /I Seq. No.451. Kathmandu: WECS

Zhicheng, Ye, 1991. ' Utilization of Biogas Slurry to Soak Seed Has Achieved a Remarkable Result/
In Biogas Forum, Vol.2/special. [Excerpted from China Biogas, 8(3), 41-42, 1990, translated
by Wu Libin].

88
 General references
(Not cited in the text)
Acharya, C.N., 1935. ' Studies on the Anaerobic Decomposition of Plant Materials.' Biochem.

Acea, MJ. and T. Carballas, 1988. * Effects of Cattle-Slurry Treatment on the Microorganisms of the
Carbon- and Sulphur- Cycles in the Soil.' In Biological Wastes 24 (1988)251-258. England:
Elsevier Applied Science Pulbishers Ltd., GB.

Anonimous, Undated: Proper Use of Biogas Slurry.

Bahadur Shahzad, 1981. Seminar-corn- Workshop on Janata Biogas Technology and Fodder
Production. Karnal: NDRI.

Bala B.K. and M.A. Satter, 1990. 'Kinetic and Economic Considerations of Biogas Production
Systems.' In Biological Waste 34 (1990) 21-38.

Brklacich, M. and Others, 1991. "Review and Appraisal of Concept of Sustainable Food Production
Systems.' In Environmental Management Vol. 15, No. 1. New York: Spring-Verlag Inc.

Brown, Norman, 1987. ' Biogas Systems in Development.' In Appropriate Technology Vol. 14,
No.3. London: IT Publications Ltd.

Brunding,5.G. and L.K.K. Rodhe, 1995. 'Comparison of Manure Handling Systems under Swedish
Conditions.' In AgBiotech News and Information Vol. 7, No. 1. [Excerpted from Journal of
Agricultural Engineering Research, 1994, 58 (3)].

Cacciatore, David A. and Mefanie A. McNeil, 1995. 'Principles of Soil Bioremediation.' In BioCycle
Vol. 8, No. 10.

Carrion Perez, P and R. Martinez Ramirez, 1995. ' Fermentation Process of Compost Controlled by a
PC In Waste and Organic Byproduct Processing Vol.7 No.l. {Excerpted from TEA
Produccion Vegetal, 1994, 90 (1).]

Chakraborty, Amulya, 1986. 'Biogas Plants Based on Nightsoil.' In Biogas from Human Waste.
(Workshop Report) New Delhi: CORT.

Daily, Gretchen C. And Paul R. Ehrfich, 1991. " Socioeconmic Equity, Sustainbility, and Earth's
Carrying Capacity.' In Ecological Applications, 6(4), 1996. Washington D.C.: ESA.

Daize, Hu, Meng Xun, Yang Kejun and Ren Shengquing, 1991. "Bio-Digestion - the Pivot of
China's Eco-agricultural Construction.' In Biogas Forum Vol. 11, No. 45, 1991.

DaSilva, Edgar ]., 1981. Biogas: its Potential and Applications for Developing Countries.' In
StamboHs, Costis, ed., Renewable Energy Sources for Developing Countries. London:
Heliotechnic Press.

Demant, Dierk, 1990. ' Biomanure from Small Biogas Plants.' In GATE 11,15-3-6, 1990.

Demant, D., 1986. ' Use of Digested Slurry From Biogas Plants.' In Biogas Forum No. 27, 1986.
Kathmandu.

89
Dev, S.P., M.K. Gupta and K.K.R. Bhardwaj, 1992. " Effect of Crop Waste and Nitrogen Levels on
the Number and Activity of Microorganisms in Soil in Wheat- Maize Cropping Sequence.'
In Biological Nitrogen Fixation and Biogas Technology. Tamilnadu: Tamilnadu Agricultural
University.

Devkota, Govinda P., 1982. "Report on Second Inspection Visit to Dome Design of Gobar Gas
Plants Constructed in Pokhara, Nepal/ In Biogas Forum:

Dewes, T., L.Schmitt, U. Valentin and E. Ahrens, 1989. "Nitrogen Losses during the Storage of
Liquid Livestock Manures.' In Biological Wastes 31. England: Elsevier Science Publishers
Ltd.

Dhanpai, D., 1992. ' Rural Energy and the Quality of Air-with Special Reference to a Tribal Area in
Tamil Nadu. In Energy Environment Monitor Vol. 8 No.l, 1992.

Dhussa, Anil. K.; 1986. " Biogas Plant Effluent Handling and Utilisation.' In Biogas from Human
Waste. (Workshop Report) New Delhi: CORT.

Dohne, E., 1990. ' Optimal Bioslurry Fertilisation in West Germany.' In Biogas Forum, Vol. 1
Special, 1990.

Domsch, K.H. and et al., 1979. 'A Comparison of Methods for Soil Microbiai Population and
Biomass Studies/ In Eingegangen. Weinheim: Verlag Chemie.

FAO7 1977. China: Recycling of Organic Wastes in Agriculture (Report on an FAO/UNDP study
tour to the Peoples' Republic of China, 28 April - 24 May 1977 (FAO Soils Bulletin 40)
Rome: FAO.

Frossard, E., S. Sinaj, L-M Zhang, and ). L. Morel, 1996. "The Fate of Sludge Phosphorus in Soil-
Plant Systems.' In Soil Science Society of America Journal, Vol. 60, No. 4, 1996.

Govilkar, Maltid, 1981. Key Note address: Why Study Biogas Technology?' In Seminar-Cum-
Workshop on Janata Biogas Technology and Fodder Production. Karnal: NDRl.

Goswami, K.P., P.S. Bhorania and K. P. Patel, 1996. * Recovery of Water and Manure From Biogas
Plant Slurry/ In Changing Villages, Vol. 15, Jan-Jun.

Gutterer, Bernard and Ludwig Sasse, 1993. 'Summary and Recommendations.' Report Biogas
Survey 1992: Cross Section Analysis of Biogas Dissemination Programmes. Bremen, FRG:
BORDA (Bremen Oversees Research and Development).

Havard-Ducfos, B., 1975. Las Plants Farrajeras Tropicales. Blume, Ed. Madrid.

Hisserich, H., 1947. " Le gaz de fumier an Ailemagne.' Land Wald und Garten, May 1947.

Horn, Thomas F., undated. ' Sludge Treatment- Soil Conditioning and Composting.' In Biogas
Production and Utilization (ed. By Eiezabeth C. Price and et al.). Ann Arbor, Mich: Ann
Arbor Science Publisher's Inc.

Hofman, G., 1988. ' Nitrogen Supply from Mineralization of Organic Matter/ In Biological Waste
26(1988).

Itrabansh, Shova, undated. Isolation of Different Types of Aerobic and Anaerobic Bacteria From
Biogas Digester Under Laboratory Condition. Kathmandu: CEDA.

90
ICIMOD, 1991. 'Biogass and the Conservation of Energy through Improved Cooking-stoves in
Nepal: Problems and Prospects/ In Report of the Seminar on Rural Energy and Related
Technologies in Nepal. Kathmandu: ADB/n, ICIMOD, WECS.

lwabuchi, K. and T.Kimura, 1995. 'Aerobic Biodegradation of Dairy Cattle Faeces (Part 1). Heat
Production Rate and Oxygen Uptake Rate/ In Waste and Organic Byproduct Processing Vol.
7, No.l. [Excerpted from Journal of the Japanese Society of Agricultural Machinery, 1994,
56(2).

Jarvenpaa, M and T. Maunu, 1995. 'The Economics of Energy Biomass Production on Set-Side
Land/ In Waste and Organic Byproduct Processing Vol. 7, No.l. [Excerpted from Biomass
tuotannon talous maatiloilla. Tyotehoseuran Julkaisuja, 1994, No. 333.]

Jiashi, Sun and Zhu Reng, 3 991. 'A Study on Applying "Biogas Fertilizer" to Prevent Plant Disease
and Insect Pests/ In Biogas Forum, Vol. 2/ Special. [Excerpted from China Biogas, 8(4), 31-
33, 1990, translated by Ren Shengquing]

Jiayu, Min and Li Zhengfang, 1991. 'A comparative Study on the Efficiencies of Fingerling Raising
with Slurry from Biogas Disgester Chicken Manure and Mixed Baits/ In Biogas Forum Vol
2/ special. [Excerpted from China Biogas, 1990, 8( 1) 36-38, translated by Min Jiayu].

Kannaiyan, S., K. Ramasamy, K. Ilamurugu, and K. Kumar, 1992. Biological Nitrogen Fixation and
Biogas Technology. Tamilnadu: Tamilnadu Agricultural University, India.

Karki, Amrit B. And Krishna M. Gautam, 1995. Effects of Slurry from Anaerobic Digestion of
Organic Wastes on Crops and Vegetables and its Residua! Effect on Soil. Kathmandu.

Khanna S., Krishna Mohan (eds), . Wealth from Waste. New Delhi: TERI

Klein, C.A.M. de, R.S.D. van Logtestijn, H.G. van de Meer and J.H. Geurink, 1996. 'Nitrogen
Losses due to Denitrification from Cattle Slurry Injected into Grassland Soil with and
without a Nitrification inhibitor. In International Journal on Plant Soil Relationship.'
m
Lichtman, Rob, 1992. ' Diffusion or Confusion: Some Thoughts on 15 years of Biogas Programs/
Biogas Forum Vol. II, No.49.

Lichtman, Rob, 1993. ' Confusion about Diffusion/ In Biogas Forum Vol. I, No.52.

Mahadevaswamy M. And L.V. Venkataraman, 1990. 'Integrated Utilization of Fruit-Processing

Wastes for Biogas and Fish Production/ In Biological Wastes 32 (1990) 243-251. England:
Eisevier Science Publishers Ltd.

Mahapatra, Krishna, 1985. 'The Puri Nightsoil Biogas Plant: A Sociological Evaluation Through A
Case Study/ In Changing Villages Vol. 7 No.6, Nov-Dec.

Marry, B., S. Recous, D. Darwis and D. Robin, 1996. l Interactions Between Decomposition of Plant
Residues and Nitrogen Cycling in Soil/ In International Journal on Plant and Soil
Relationship 181.

Mazumdar, N.B. and Yashwant Singh, 1986. 'Promotional Strategy on Biogas Programmes.' In
Biogas from Human Waste (Workshop Report). New Delhi: CORT.

91
Meng Xun, Hu Daize, Yang Kejung and Ren Shengqing, 1991. 'Biogas and the Construction of
Ecological Agriculture in China.' In Biogas Newsletter No. 36, April 1991. Kathmandu
Nepal.

Mengei, K., 1996. 'Turnover of Organic Nitrogen in Soils and its Availability to Crops/ In
International Journal on Plant and Soil Relationship 181. Dordrecht: Kluwer Academic
Publishers, Netherland.

Moser, Mark A., 1996. Biogas Utilization, in Lusk, P., P. Sheeler, C. Rivard {eds.) , Deploying
Anaerobic Digesters: Current Status and Future. Colorado: National Renewalbel Energy
Laboratory.

Mosey, Frank E., 1996. ' Environmental Impacts of Anaerobic Digestion and the Use of Anaerobic
Residues as Soil Amendment.' In Lusk, P., Wheeler P., Rivard c (eds.) Deploying Anaerobic
Digesters: Current Status and Future. Colorado: National Renewable Energy Laboratory.

Pluschke, Peter, 1990. 'Contamination in Sewage Sludge and Bioslurry.' In Biogas Forum Vol.
I/Special.

Pokharel, R.K. and R.P. Yadav, 1991. Application of Biogas Technology in Nepal: Problems and
Prospects. Kathmandu: IC1MOD.

Polak, Hans, 1992. ' Confusion about Diffusion: Some Remarks on Rob Lichtman's article on 15
years of Biogas Programmes/ In Biogas Forum Vol.1., No51.

Pry, L.J., 1975. Practical Building of Methane Power Plants for Rural Energy Independence.
Andover, Hampshire, UK Chapel River Press.

P., Venkata Ramaiah, Suresh Kumar M. and Gopikrishna T, 1994. 'Bio Village - A New Perspective
for Rural Development.' In Changing Villages Vol. 13, No. 1.

Rawat, B.S., 3 981. 'Gobar Gas-Cum-Compost Plant and the Economics of its Outputs.' Seminar
Com Workshop on Janata Biogas Technology and Fodder Production. Kamal: NDRI.

Rajabapaiah, P, S. Gayakumar and Amuiya K.N. Reddy, 1981. 'Biogas Electricity.' In Renewable
Energy Sources for Fuels and Electricity. Washigton D.C.: Island Press, Lovelo, California.

Santhanakumar, G., G. Kanthaswamy and T. Muthumaneksha, 1993. 'Studies on the Residual Effect
of Organic Manures and Inorganic Fertilizers on Blackgram.' In Biogas Slurry Utilsation.
New Delhi:CORT.

Santhanakumar, G. And S. Mutharasan, 1993. ' Impact of Biogas Slurry and Inorganic Fertilizer on
the Soil Microorganisms/ In Biogas Slurry Utilsation. New Delhi:CORT.

Sasse, Ludwig, 1993. ' Comparison of Utilising Biogas Plants by Farmers in India and Indonesia/ In
Biogas Forum Vol. IV., No. 55, 1993.

Sasse, Ludwig, 1990. ' Evaluation of Biogas Programmes - Methodology and Criteria. In GATE 11,
15-3-6, 1990A

Sasse, Ludwig, 1989. ' Evaluation of Ecological Benefits. In Biogas Forum No. 37.

92
Saxena, K. K., K. Nath and S.K. Srivastava, 1989. 'The Effect of Using Dung from Cattle Fed
High-> Law-or No-Concentrate Rations, on the Quality and Nutritive Value of Slurry from
a. Biogas Plant.' In Biological Wastes 28 (1989) 73-79.

Schreier, H., P.B. Shah, and S. Brown, 1995. Challenges in Mountain Resource Management in
Nepal: Process, Trends, and Dynamics in Middle Mountain Watersheds. Proceedings of a
Workshop, April 10-20, 1995. Kathmandu: ICIMOD.

Schreier, H., P.B. Shah, LM. Lavkulich and S. Brown, 1994. Maintaining Soil Fertility Under
Increasing Land Use Pressure in the Middle Mountains of Nepal.' In Soil Use and
Management (1994) 10, No. 3, 137-142. Huddensfield England: CAB International
(Published for the British Society of Soil Science).

Sharma, U.P., 1981. 'Complete Recycling of Cattle-Shed Wastes Through Biogas Plant.' Seminar
Com Workshop on Janata Biogas Technology and Fodder Production. Kamal: NARI.

Sherchan, D.P. and G.B. Gurung, 1996. ' Effect of Five Years Continuous Application of Organic
and Inorganic Fertilizers on Crop Yields and Physico-Chemical Properties of Soil Under
Rainfed Zaize/Millet Cropping Pattern.' Draft Report Presented at the Summer Crops
Workshop at the National Maize Research Programme, Pampur.

Sherchan, D.P. and G.B. Gurung, 1995. 'An Integrated Nutrient Management System for Sustaining
Soil Fertility: Opportunities and Strategy for Soil Fertility Research in the Hills. 'In
Challenges in Mountain Resource Management in Nepal: Process, Trends, and Dynamics in
Middle Mountain Watersheds. Proceedings of a Workshop, April 10-20, 1995. Kathmandu:
ICIMOD.

Shi zhengshan, Zhang Ping and Huang Changke Li Peiqian, 1992. ' Study on Prevention and Cure of
Wheat Gibberella Disease with Biogas-Slurry. In Biogas Forum Vol (2) special. [Excerpted
from China Biogas, 1991, 9 (1), 11 -14, translated by Zhang Mi.

Shroff, V.N., 1993. 'Organic Manures and Biofertilizers - Only Solution to Many Problems.' In
Changing Village, July-Sept., 96.

Sihe, Jia, 3 991." Technology of Planting the Pond Lotus Roots with Digester Slurry.' In Biogas
Forum, Vol.2/special. [Excerpted from China Biogas, 8(4), 37, 1990, translated by Song
Yuhua].

Subedi, Kalidas, 1993. 'Results of Various Composting Experiments Carried Out at Lumle.' A
Review Papaer No. 93/1. LARC.

Takahashi, Shigeru and S. Yamamuro, 1995. ' Quantification of Effect of Temperature and Air-
Drying Treatment in Paddy Soils on Mineralization of Soil Organic Nitrogen.' In ]AEQ 29
(2).

van Nes, Wim J. .1996. 'Biogas Support Programme: Results in the Period July 1992-1995'. In
Biogas and Natural Resource Management, Number 51

Whitmore, A.P. and J.J. Schroder, 1996. 'Modelling the Chang in Soil Organic C and N and the
Mineralization of N from Soil in Response to Applications of Slurry Manure.' In
International Journal on Plant and Soil 184:185-194. Kluwer Academic Publishers. Printed
Dordrecht in the Netherlands.

93
Wong, Mamie Lau, 187. 'Calculation of the Quantity of Input for Biogas Plants.' In Biogas
Newsletter No. 25, Nov. 1987. Kathmandu.

Yu, Min Jia, 1992. 'The Development of Fish-Breeding with Bio-Manure in China.' In Biogas Forum
Vol (2) special. [Excerpted from China Biogas, 1991, 9 (4), 1-4, translated by Zhang Mi.

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 Prologue
The field of slurry utitilization is an important one if the perceived twin benefits of biogas
technology is to be fully utilized. The theoretical and conceptual bases behind biogas and slurry
promotion is essentially justified in view of the finite nature of commodities we use for both fuel and
mineral fertilizer. In fact, biogas and bioslurry both have potentials to contribute in our
contemporary strivings for a sustainable society.

Lack of comparative studies of the effects on crop production of bioslurry compost, fresh liquid
slurry, sun-dried slurry and ordinary compost are lacking. Nutritional analysis and field results in
many cases are of dubious value because of the absence of proper research designs. This situation
can be cleared only with experimentations footed on rigorous scientific principles.

The newness of slurry research is evident from the fact that literature is full of idiosyncratic usage of
the terms like these: "sludge', 'bioslurry', 'biogas slurry', 'biodigested slurry', 'sun dried slurry' 'wet
slurry', 'effluent', 'slurry' 'biomanure' 'biosol' 'biol' ' digested slurry' ' biofertilizer 'sludge manure'
'residual manure', 'liquid manure', 'fresh slurry', 'digested residue', 'digested sludge' 1 organic
manure', etc. To be sure these are all organic manures/fertilisers and also these are biofertilisers. But
slurry by definition is the mixture of solids and liquids. And it remains slurry as long as this mixture
maintains a fairly constant proportion of liquid and solid in an accepted range. But then the literature
often use biogas 'slurry' in such a loose manner (without proper explanations) that often times it is '
slurry' even if t is sun-dried with a drastically reduced moisture content. As 1 slurry' in its literal
meaning is different from (in terms of moisture, the chemical stages of nutrients and their
availability to plant) say a sundried form ( some how moist and wet substance with charges in its
physical and chemical/nutritional composition), loose and unqualified usage of the terminologies
makes slurry research results ambiguous and vague. The literature frequently distinguishes the
differential effects of this biproduct of biogas plants. Yet ' BDS' or ' plain slurry' or 'bioslurry' are
used no matter whether they are completely dried powdery forms or in the form of pastes or a free
flowing mixture. The matter is further compounded by the use of the term ' sludge'. The residue
when slurry is dewatered is called sludge in many cases. In others, the sedimented (residual) portion
of slurry is taken as sludge. There are no problems with these. Problem arises when sludge' most
oftentimes is used, indiscriminately and interchangeably, for 'slurry' in research reports. Some
conceptual definitions providing boundaries between the terms, between the lay usage and scientific
definitions, are in the need in slurry research. The is how science advances-the clearing of the
terminological jungle is an urgent task before conducting any fruitful research. The term ' fresh
slurry' is also frequently used in the literature. There will be not much problem if ' fresh' is defined in
terms of the time slurry is taken out from the digester. Problem arises when fresh slurry is also
sometimes taken as filtered or dewatered solid biproduct and entered into the research protocols as '
fresh slurry.' In others, the terms ' liquid manure' ' liquid slurry' are also used without qualifying
whether it is the slurry as it comes out from the digester or whether it is a deliberately diluted,
liquidified material, or the liquid obtained from the dewatering process. Ambiguity of research result
compounds when sometimes wet' or ' moist' is taken as ' liquid.'.

In the Indian literature the term 'demonstration' is overwhelmingly used since the inception of the
large scale farmer participatory research in slurry utilisation in crop production in the Eighties.
Traditional agricultural extension tells us that a demonstration is usually an educational method in
which proven and credible technologies are demonstrated in farmer's field. It seems from the review
that the technology is just emerging. Yet, terms such as 'testing' 'trials' and 'experiments', '
verification trials', etc., are seldomly used. Of course, there will be " demonstration effects' of those
trials and experimentations. It is just that in the accepted conventional academic parlance these
activities were not 'demonstrations' but "trials' and 'experimentations'.

95
For any research agenda in the natural sciences (as against in the social sciences where the concepts
and terminologies have ‘sensitizing’ responsibilities), it is as important aspect that terminological
ambiguities be cleared before proceeding ti the research work and pubilishing the reports.

96