GROWTH, YIELD, AND QUALITY OF ONION (Allium cepa L.

) AS
INFLUENCED BY INTRA-ROW SPACING AND NITROGEN
FERTILIZER LEVELS IN CENTRAL ZONE OF TIGRAY, NORTHERN
ETHIOPIA

MSc. THEIS

GUESH TEKLE

OCTOBER 2015
HARAMAYA UNIVERSITY, HARAMAYA
Growth, Yield, and Quality of Onion (Allium Cepa L.) as Influenced by Intra-
row Spacing and Nitrogen Fertilizer Levels in Central Zone of Tigray,
Northern Ethiopia

A Thesis Submitted to the College of Agriculture and Environmental Sciences

School of Plant Sciences, Post Graduate Directorate
HARAMAYA UNIVERSITY

In Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE IN AGRICULTURE
(HORTICULTURE)

Guesh Tekle

OCTOBER 2015
Haramaya University, Haramaya

ii
 HARAMAYA UNIVERSITY

SCHOOL OF GRADUATE STUDIES

As thesis research advisers, we hereby certify that we have read and evaluated the thesis
prepared, under our guidance by Guesh Tekle, which is entitled “Growth, Yield and Quality
of Onion (Allium cepa L.) as Influenced by Intra-row Spacing and Nitrogen Fertilizer
Levels in Central Zone of Tigray, Northern Ethiopia”. We recommend that the thesis be
accepted as it fulfills the requirements.

Prof Nigussie Dechassa (PhD) ______________ _______________

Major Adviser Signature Date

Gebremedhin Woldewahid (PhD) _________________ ____________

Co-adviser Signature Date

As members of the Board of Examiners of the MSc. Thesis Open Defense Examination, we
certify that we have read and evaluated the thesis prepared by Guesh Tekle and examined the
candidate. We recommend that the thesis be accepted as it fulfills the requirements for the
Degree of Master of Science in Agriculture (Horticulture).

_________________ _________________ _____________

Chairperson Signature Date

__________________ _________________ _______________

Internal Examiner Signature Date

________________ _________________ ____________

External Examiner Signature Date

Final approval and acceptance of the thesis is contingent up on the submission of its final copy of the
thesis to the council of graduate program (CGP) through the departmental or school of graduate
committee (DGC or SGC).

iii
 DEDICATION

I dedicate this thesis manuscript to my mother Guey Weldegerima for her advice and for
nursing me with affection and care and for her partnership in the success of my life.

iv
 STATEMENT OF THE AUTHOR

First, I declare that this thesis is a result of my work and all other sources of material and
information used for writing it have been duly acknowledged. This thesis has been submitted in
partial fulfillment of the requirements for MSc degree at Haramaya University and is deposited at
the university’s library to be made available to borrowers under the rules and regulations of the
library. I solemnly declare that this thesis has not submitted to any other institution anywhere for
the award of any academic degree, diploma, or certificate.

Brief quotations from this thesis are allowed without requiring special permission provided that
an accurate acknowledgment of source is made. Requests for permission for extended quotations
from or reproduction of this manuscript in whole or in part may be granted by the head of the
Department of Plant Sciences or the dean of the School of Graduate Studies when in his or her
judgment the proposed use of the material is for a scholarly interest. In all other instances,
however, permission must be obtained from the author.

Name: Guesh Tekle

Place: Haramaya University
Signature ----------------------
Date of submission: --------------------------------

v
 BIOGRAPHICAL SKETCH

The author, Guesh Tekle, was born on 17 June 1984 at Axum, Central Zone of Tigray to his
father Tekle Gebregziabher and his mother Guey Weldegerima. He attended Elementary
education (grades one to six) at Mytruengi Elementary School from 1993-1996, junior secondary
education (grades seven to eight) at Mahbere-Dego School from 1997-1998, and secondary
education at Axum Comprehensive Secondary School from 1999-2002. After completing his
elementary and secondary education, he joined the College of Agriculture and Veterinary
Medicine of Jimma University in 2003, and graduated with the degree of Bachelor of Science
(BSc) in Horticulture in July 2006.

Immediately after graduation in 2007, he was employed by South Tigray, Alamata Woreda
Office of Agriculture and Rural Development as a vegetable and fruit expert, where he worked
up until 10 May 2009. In May 2009, he joined Tigray Agricultural Research Institute (TARI) as
a researcher in Horticulture. He continued working at TARI up until he joined the School of
Graduate Studies of Haramaya University in 2011 to pursue a study leading to the degree of
Master of Science (MSc) in Horticulture.

vi
 ACKNOWLEDGEMENTS

Foremost, I would like to express my sincere gratitude to my major adviser Prof. Nigussie
Dechassa for the continuous support he provided me throughout the period of my study with
great affability, enthusiasm, and immense knowledge. His guidance, comments, suggestions and
insightful advice helped me at all stages of my research work and during the writing of my thesis.
I would also like to thank my co-adviser Dr. Gebremedhin Woldewahid for his encouragement,
insightful comments and advice in preparing the thesis. His suggestions, guidance, insightful
ideas, and editorial supports were helpful for me to complete the write up of the thesis.

I would like to take this opportunity to thank the Livestock and Irrigation Value Chain Project
(LIVES) for sponsoring my research. I would also like to express my gratitude to Tigray
Agricultural Research Institute, which provided with leave of absence to my MSc study and for
paying my salaries regularly while I was on the study leave.

My special thanks also go to staff members of Axum Agricultural Research Center specially
Nahom Weldu, Haftamu Hailekiros, Atakilti Mekonen, Muruts Belay, Kiros Welday, Tesfuom
Fitsum, Fasikaw Belay, Tesfay Araya, Atsede Teklu and others who helped during preparation of
the research site, transplanting onion seedlings, data collection, and harvesting. I would also like
to express my gratitude to drivers of the Axum Agricultural Research Center particularly for
Gebregziabher Atsbeha and Mulualem Tadele for their supporting me with facilitation of
transport services starting from transplanting till the final harvesting.

Last, but not least, I would like to thank my family members for their unlimited support and help
throughout the period of my study. Above all, I praise and glorify the Almighty and Merciful
God for providing me with the patience and stamina to complete my MSc work.

vii
 ABBREVIATIONS AND ACRONYMS

ANOVA Analysis of Variance

AxARC Axum Agricultural Research Center

AVRDC Asia Vegetable Research and Development Center

CEC Cation Exchange Capacity

CIMMYT Center of International Maize and Wheat Improvement

CSA Central Statistical Agency

EARO Ethiopian Agricultural Research Organization

FAO Food and Agricultural Organization

HI Harvest Index

DMRT Duncan Multiple Range Test

MoARD Ministry of Agriculture and Rural Development

MRR Marginal Rate of Return

MARR Minimum Acceptable Rate of Return

NUE Nitrogen Use Efficiency

SAS Statistical Analysis System

TSP Triple Super Phosphate

TSS Total Soluble Solids

viii
 TABLES OF CONTENT

STATEMENT OF THE AUTHOR v

BIOGRAPHICAL SKETCH vi
ACKNOWLEDGEMENTS vii
ABBREVIATIONS AND ACRONYMS viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF TABLES OF APPENDIX xiii
1. INTRODUCTION Error! Bookmark not defined.
2. LITERATURE REVIEW 5
2.1. Description of Onion Crop 5
2.2. Environmental Requirements of Onion 6
2.3. Importance and Production Status of Onion in Ethiopia 8
2.4. Response of Onion to Nitrogen Application 9
2.4.1. Roles of nitrogen in onion nutrition and growth 9
2.4.2. Response of onion to nitrogen fertilization 10
2.5. Effect of Plant Spacing on Onion Yield and Yield Components 13
2.6. Response of Onion to Interaction Effect of Nitrogen and Plant Spacing 17
3. MATERIALS AND METHODS 19
3.1. Description of the Study Area 19
3.2. Experimental Materials 20
3.2.1. Planting material 20
3.2.2. Fertilizer material 20
3.3. Treatments and Experimental Design 20
3.4. Management of Experimental Field 21
3.5. Soil Sampling and Analysis 22
3.6. Data Collection 23
3.6.1. Phenology and growth parameters 23
3.6.2. Yield and yield components 24

ix
 3.7. Data Analysis 26
4. RESULTS AND DISCUSSION 27
4.1. Physico-Chemical Properties of the Experimental soil 27
4.2. Phenology and Growth Characters 28
4.2.1. Plant height 28
4.2.2. Leaf number per plant 29
4.2.3. Leaf length 30
4.2.4. Leaf diameter 31
4.2.5. Shoot dry matter yield 32
4.2.6. Dry total biomass yield 34
4.2.7. Days to maturity 35
4.2.8. Bolting percentage 36
4.2.9. Stand count percentage 37
4.3. Yield and Yield Related Traits 39
4.3.1. Average bulb weight 39
4.3.2. Bulb diameter 40
4.3.3. Bulb neck diameter 41
4.3.4. Bulb dry matter yield 41
4.3.5. Total bulb yield 43
4.3.6. Unmarketable bulb yield 45
4.3.7. Marketable bulb yield 45
4.3.8. Under size bulb yield (< 20 g) 52
4.4. Harvest Index 53
4.5. Total Soluble Solid 54
4.6. Correlation Analysis 56
4.7. Partial Budget Analysis 58
5. SUMMARY AND CONCLUSION 61
6. REFERENCES 64
7. APPENDICES 73

x
 LIST OF TABLES
Table Page

1. Treatment combinations, number of plants m-2, number of plants per plot and plant 21
population per hectare
2. Chemical characteristics of the experimental soil 27
3. Main effect of intra-row spacing and nitrogen fertilizer levels on plant height of onion 29
4 Interaction effect of intra-row spacing and nitrogen fertilizer levels on leaf number per 33
plant, leaf length, leaf diameter and shoot dry weight yield of onion
5. Interaction effect of intra-row spacing and nitrogen fertilizer levels on dry total 37
biomass, days to maturity and bolting percentage of onion
6. Main effect of intra-row spacing and nitrogen fertilizer levels on stand count 39
percentage of onion
7. Interaction effect of intra-row spacing and nitrogen fertilizer levels on average bulb 43
weight, bulb diameter, neck diameter and bulb dry weight yield per plant of onion
8. Interaction effect of intra-row spacing and nitrogen fertilizer levels on marketable, 47
unmarketable and total bulb yield of onion
9. Interaction effect of intra-row spacing and nitrogen fertilizer levels on marketable 52
bulb size distribution of onion
10. Interaction effect of intra-row spacing and nitrogen fertilizer levels on under sized 56
bulb yield, harvest index and total soluble solid yield of onion
11. Partial budget and MRR analysis for fertilizer rate and intra row spacing trial on 60
marketable yield of onion

xi
 LIST OF FIGURES
Figure Page

1. Map of the Study Area 19

xii
 LIST OF TABLES OF APPENDIX

Appendix Table Page

1. Mean squares of analysis of variance for leaf length (LL), leaf diameter (LD), plant 73
height (PH), leaf number per plant (LN), bolting percentage (BP) and stand count
percentage (SCP)
2. Mean squares of analysis of variance for yield and yield related traits of onion 73
3. Mean squares of analysis of variance for marketable and unmarketable size distribution 74
of onion
4. Mean squares of analysis of variance for shoot dry weight per plant (SDWPP), harvest 74
index (HI), Dry total biomass (DTB), Total soluble solids (TSS), Days to maturity
(DTM) and Bulb dry weight per plant (BDWPP)
5. Simple correlation between yield, yield components and growth characters 75

xiii
 GROWTH, YIELD, AND QUALITY OF ONION (ALLIUM CEPA L.) AS
INFLUENCED BY INTRA-ROW SPACING AND NITROGEN
FERTILIZER LEVELS IN CENTRAL ZONE OF TIGRAY, NORTHERN
ETHIOPIA

ABSTRACT
Haphazard and inappropriate plant spacing and poor soil fertility management practices are
among the major factors constraining onion production in the Central Zone of Tigray. Therefore,
a field experiment was conducted in Axum district from October to March 2014 to assess the
influence of intra-row spacing (2.5, 5, 7.5, 10 and 12.5 cm) and nitrogen rate (0, 41, 82 and 123
kg N ha-1) on growth, bulb yield, and quality of onion. The experiment was laid out in a
randomized complete block design (RCBD) of factorial arrangement with three replications. The
main effects of nitrogen rate and intra-row spacing influenced only the plant height and stand
count significantly (P < 0.01). The tallest plants (46.70 cm) were obtained from plants treated
with 82 kg N ha-1 as well as those spaced at 7.5 cm intra-row spacing (43.78 cm). The highest
stand count (90.33%) at harvest was recorded from plots that received 82 kg N ha-1 and spaced
at 12.5 cm (98.04%). Nitrogen rate and intra-row spacing interacted to significantly (P < 0.01)
to influence all parameters. Thus, increasing the rate of nitrogen across the increasing intra-row
spacing significantly prolonged days to maturity, enhanced average bulb weight, bulb diameter,
bulb neck diameter, leaf number per plant, leaf diameter, shoot dry matter, and dry total biomass
yield. In general, the highest values of these parameters (126.67, 123.85 g, 6.05 cm, 1.35 cm,
12.57, 1.38 cm, 3.22 g and 13.08 g, respectively) were attained in response to the application of
123 kg N ha-1 and 12.5 cm intra-row spacing. However, their least values (100, 23.99 g, 2.33 cm,
0.68 g, 6.60, 0.47 cm, 0.73 g, and 2.72 g, respectively) were obtained at 0 kg N ha-1 and 2.5 cm
intra-row spacing. The highest value of bolting (31.95%) was observed from the application of 0
kg N ha-1 and plant spacing of 2.5 cm. Increasing the N rate across the increasing intra-row
spacing increased the yields of over-sized bulbs whereas decreasing the yields of small-sized,
under-sized bulbs and unmarketable bulb yield. The highest yield of over-sized bulbs (4.03 t ha-1)
was recorded at 123 kg N ha-1 and the intra-row spacing of 12.5 cm. Whereas, the highest yield
of medium sized (28.27 t ha-1) and large sized bulb yield (8.03 t ha-1) was obtained both at 82 kg
N ha-1 and plant spacing of 5.0 cm and 7.5 cm, respectively. The total and marketable bulb yields
increased markedly across the increasing rate of nitrogen and intra-row spacing only up to 82
kg N ha-1 and 5.0 cm intra-row spacing which attained maximum values of (39.51 t ha-1 and
39.69 t ha-1), respectively and beyond which their yields decreased significantly. However, total
bulb yield decreased as nil nitrogen level interacted with across the increasing of intra-row
spacing. Thus, the lowest total (18.89 t ha-1) and marketable bulb yields (17.93 t ha-1) were
obtained from plants that received no nitrogen at the intra-row spacing of 12.5 cm and 2.5 cm,
respectively. The highest value of harvest index (79.98%) was produced at 82 kg N ha-1 at the
plant spacing of 5.0 cm and 7.5 cm. However, the highest total soluble solid (13.57 0Brix) was
obtained at 123 kg N ha-1 and intra-row spacing of 2.5 cm. In conclusion, as the partial budget
analysis revealed that the highest net benefit with low cost of production was obtained in
response to the application of 82 kg N ha-1 and the intra-row spacing of 10 cm and was optimum
for producing the crop in the study area.
Key words: Onion, intra-row spacing, nitrogen, marketable yield, bulb size distributions

xiv
 1. INTRODUCTION

Onion (Allium cepa L.) is one of the most important vegetable crops commercially grown in
the world. It probably originated from Central Asia between Turkmenistan and Afghanistan
where some of its relatives still grow in the wild. Onion from Central Asia, the supposed onion
ancestor had probably migrated to the Near East (Grubben and Denton, 2004; Bagali et al.,
2012).

The crop onion is a popular vegetable and its bulb is used raw, sliced for seasoning salads, and
cooked with other vegetables and meat. Onion bulbs are essential ingredients in many African
sauces and relishes. The leaves, whole immature plants called ‘salad onion’ or leafy sprouts
from germinating bulbs are used in the same way. In some parts of West Africa, leaves still
green at bulb harvest are propounded, and then used to make sun-dried and fermented balls,
which are used later for seasoning dishes. Sliced raw onions have antibiotic properties, which
can reduce contamination by bacteria, protozoa or helminths in salads (Grubben and Denton,
2004).

Onions are day length sensitive, several onion types exist depending upon the latitude at which
they grow. It is estimated that around the World, over 3,642,000 ha of onions are grown
annually. On a worldwide scale, around 80 million metric tons of onions are produced per
year. China is by far the top onion producing country in the world, accounting for
approximately 28% of the world’s onion production, followed by India, USA, Iran, Egypt,
Turkey, Russia, Pakistan, Netherlands and Brazil. The worldwide onion exports are estimated
at around 7 million Metric tons. The Netherlands is the world’s largest onion exporter with a
total of around 220,000 Metric tons followed at a distance by India (FAO, 2013).

Onion has economically important role in Ethiopia. The country has enormous potential to
produce the crop throughout the year both for domestic use and export market. Ever since the
crop is distributed to different parts of the country, it is widely cultivated as a source of
income by many farmers in many parts of the country as a whole. Onion production also
contributes to commercialization of the rural economy and creates many off-farm jobs
 2

(Lemma and Shimeles, 2003; Nikus and Mulugeta, 2010). Onion production in the country is
increasing from time to time. During the 2013/2014 cropping season, the total area under
onion production was estimated to be 24, 375.7 ha with an average yield of about 9.02 tons per
hectare and estimated a total production of greater than 2, 19, 735.27 tons (CSA, 2014).

Nutrients play a significant role in improving productivity and quality of vegetable crops.
Onions are the most susceptible crop plants in extracting nutrients, especially the immobile
types, because of their shallow and unbranched root system; hence they require and often
respond well to addition of fertilizers (Brewster, 1994; Rizk et al., 2012). Therefore, optimum
fertilizer application and cultivation of suitable varieties with appropriate agronomic practices
in specific environment are necessary for obtaining good yield of onion.

Nitrogen (N) and phosphorus (P) are often referred to as the primary macronutrients because
of the probability of plants being deficient in these nutrients and the large quantities taken up
from the soil relative to other essential nutrients (Marschner, 1995). Nitrogen plays an
important role for optimum yield of onion and is found to be essential to increase the bulb size
and yield. Increasing nitrogen application rates significantly enhances plant height, number of
green leaves per plant and weight of bulb, marketable yield and also total soluble solids
(Nasreen et al., 2007; Al-Fraihat, 2009).

In addition to nitrogen, plant spacing is an important factor determining onion yield and
quality. An essential aspect of any crop production system is the development of a crop
canopy that optimizes the interception of light, photosynthesis, and the allocation of dry matter
to harvestable parts. A crop canopy is commonly managed by manipulating row spacing and
plant population; as plant density increases, yield per unit area increases and will approach an
upper limit, the plateau. Then, the yield per unit area declines since yield per plant tends to
decrease with further increase in the plant density because of competition for growth factors
between adjacent plants (Silvertooth, 2001). Thus, spacing is an important factor for the
production of onion since it affects both bulb yield and quality. Plating density greatly
influences quality, texture, taste and yield of onion even within a particular variety (Saud et
al., 2013). Yield responses to plant population need to be known for practical purposes, as
 3

planting density is a major management variable used in matching crop requirements to the
resources by the environment (Smith and Hamel, 1999). Coleo et al. (1996) reported that the
highest commercial bulb yield was recorded at a higher planting density, but the highest
proportion of large bulbs and average bulb weight at lower planting density.

The enhancement of onion production and productivity can be related to different growth
factors. Onion dry bulb production depends on nutrient requirements, location of production,
variety, soil type, agronomic practices etc. Thus, research should be undertaken to determine
specific application rates for individual fields since it is important to avoid over fertilization
with nitrogen or phosphorus, as this will contribute to increased pest attacks and stimulation of
succulent growth that may predispose the plant to damage by field or storage pathogens Ware
and McCollum (1980). On the other hand, under fertilization should also be avoided lest low
yield and quality of the crop are obtained.

The use of appropriate agronomic management has an undoubted contribution to increased

crop yields. One of the major problems to onion production is improper agronomic practice
used by farmers. The optimum level of any agronomic practice such as plant population,
planting date, harvesting date, and fertilizer of the crop varies with environment, purpose of
the crop and cultivar. Optimum plant spacing and nitrogen recommendations have been
formulated for onion particularly in the Rift Valley region of Ethiopia, which is double row
spacing of 10 cm between plants and 20 cm between rows and application of 46 kg N ha-1 and
92 kg P2O5 ha-1 (Lemma and Shimeles, 2003; Nikus and Mulugeta, 2010). However, these
recommendations cannot be directly adopted for the soil and growing conditions of the Central
Zone of Tigray, which are different from the conditions in the Rift Valley region. This means
that, it is very difficult to give general recommendations that can be applicable to the different
agro-ecological zone (Upper Awash Agro-Industry Enterprise, 2001). Therefore, to optimize
onion productivity in the study area, a specific package of recommendation of nitrogen
fertilizer and plant spacing is required (Gupta et al., 1994; Lemma and Shimeles, 2003).

Onion is one of the most important vegetable crops cultivated mostly under irrigated
conditions in Axum District in Central Zone of Tigray Region. There are many production
 4

constraints responsible for low yield per unit area in the Districts. According to Problem
Appraisal of Axum Agricultural Research Center (Unpublished, 2012), different agronomic
practices are undertaken to produce the crop in the District. For example, growers use different
levels of inorganic fertilizers for production of different vegetables under irrigation
particularly for onion production. The farmers often apply between 100-200 kg ha-1 of DAP
and 50-150 kg ha-1 Urea. However, a few of the farmers use higher doses of these fertilizers,
and a significant number of farmers use small doses of N fertilizer in the form of Urea. This
shows no specific nitrogen levels are applied by smallholder farmers in the District. However,
the blanket recommended rates of fertilizers are 200 kg ha-1 of DAP and 100 kg ha-1 Urea
(Nikus and Mulugeta, 2010). Farmers in the district also grow onion using double row
planting method at the spacing of 40 cm between furrows and 20 cm between rows on the
ridge. However, the different growers use different spacing for improving the yield of onion.

Onion is traditionally grown at the recommended spacing of 40 cm x 20 cm x 10 cm in

Ethiopia (Lemma and Shimeles, 2003). However, farmers in Axum District use narrower
intra-row spacing. Farmers’ reasons for using narrow plant spacing are to minimize the
number of oversized bulbs produced in wider plant spacing and for producing bulbs with
higher yields and optimum sizes per unit area and for effective use of the limited irrigable
land. Moreover, oversized bulbs have little market demand in the local markets of Axum and
its environs. The reasons for less market demand of large onion bulbs have not been
documented, but may be attributed to the poor shelf life and other quality attributes of large
bulbs. At present, onion growers in the Central Zone of Tigray produce onions with the
application of blanket recommendation of nitrogen fertilizer rates and intra-row spacing or
using N rates and spacing which they feel as best for obtaining higher yields. Therefore, the
present study was initiated with the following objectives:
• To assess the effect of intra-row spacing and nitrogen fertilizer level on growth, yield
and quality of onion; and
• To identify the appropriate intra-row spacing and nitrogen fertilizer rate that improves
yield and quality of onion.
 5

2. LITERATURE REVIEW

2.1. Description of Onion Crop

Onion (Allium cepa L.) belongs to the family Alliaceae or Amaryllidaceae which is one of the
most important monocotyledonous crops. It belongs to the genus Allium and recent estimations
accept about 750 species in the genus Allium, among which onion, Japanese bunching onion,
leeks, and garlic are the most important edible Allium crops. And about 60 taxonomic groups
at sub-generic, sectional and sub-sectional rank (Baloch, 1994; Rabinowitch and Currah,
2002). Onion from central Asia, the supposed onion ancestor had probably migrated to the
Near East. Then it was introduced to India and South-East Asia; and into the Mediterranean
area and from there to all the Roman Empire (Grubben and Denton, 2004).

Onion is a cross-pollinated cool season vegetable crop. It is the oldest known vegetable. Onion
is an indispensable and important vegetable item which is used in every kitchen therefore its
constant demand always remains throughout the year. Besides its high food value, it is also a
good source of income for vegetable growers. It can be eaten as green leaves, bulbs that are
mature and immature which can be eaten as fresh and also can be used in preparation of
different dishes. The pungency of the onion bulbs is due to the presence of a volatile oil that is
allylpropyl disulfide (Baloch, 1994). The onion has its own distinctive flavor and used in
soups, dishes, salad and sandwiches and is cooked alone as a vegetable. It is consumed at its
young green stage or after its full development and maturity when it is harvested in the form of
a dry bulb. The mature bulbs contain some starch, appreciable quantities of sugar, some
protein, and vitamins A, B and C (Jilani et al., 2010).

Onion is a shallow rooted, biennial crop which is grown as annual. The leaves are long, hollow
with widening, overlapping bases. The tubular leaf blades are flattened on the upper surface,
and the stem of the plant also is flattened. Roots arise from the bottom of the growing bulb.
Leaf initiation stops when the plant begins to bulb. The base of each leaf becomes one of the
“scales” of the onion bulb, so the final bulb size depends in part on the number of leaves
present at bulb initiation. The leaf base begins to function as a storage organ at bulb initiation,
 6

so the size of the leafy part of the plant also influences bulb size. Thus, the more leaves
present and the larger the size of the plant at the onset of bulb initiation, the larger will be the
bulbs and the greater will be the crop yield (Hamasaki et al., 1999).

The onion develops distinct bulbs depending on the varieties. These bulbs are varying in size
(small, medium and large). Bulb weight may be one kg in some Southern European cultivars,
and the shape covers a wide range from globose to bottle like and to flattened disk-form. The
color of the membranous skins may be white, silvery, buff, yellowish, bronze, rose red, purple
or violet. The color of the fleshy scales can vary from white to bluish-red. There is also much
variation in flavor and keeping or storage ability of the bulbs ((Baloch, 1994; Rabinowitch and
Currah, 2002).

2.2. Environmental Requirements of Onion

Onion can be grown in a wide range of climatic environments, but it thrives best at mild
climate without excessive rainfall or extremes of heat and cold. Onion is a cool season crop
that has some frost tolerance but is best adapted to a temperature range between 13 and 24 0C.
Optimum temperatures for early seedling growth are between 23 and 27 0C; growth is slowed
at temperatures above 30 0C. Acclimatized plants are able to tolerate some freezing
temperature. Best production is obtained when cool temperature prevails over an extended
period of time, permitting considerable foliage and root development before bulb formation
starts. After bulb formation begins, high temperature and low relative humidity extending into
the harvest and curing period are desirable (Purseglove, 1985; Rubatzky and Yamaguchi,
1997; Jilani et al., 2010).

Onions can be grown on a wide range of soils, varying in texture from coarse-grained sands to
clays. Lighter soils are easy to manage. Soils should be 45-60 cm deep and well drained. Soils
with high water holding capacity are better able to provide moisture to the shallow rooting
system but must also drain well to be suitable. Growth is retarded when available soil moisture
is low, but onions are also sensitive to a high water table or water logging. Uniform moisture
availability about 400-800mm per crop is conducive to large bulb size and high yields.
 7

Favorable soil pH is about 6.5–8.0 in mineral soils (Rubatzky and Yamaguchi, 1997; Savva
and Frenken, 2002).

Light and temperature influence the process of bulbing. Both factors must be at optimum for
the initiation of the bulbs. Cool conditions with long days are normally important for
production, although there are cultivars that tolerate warm conditions and short day-lengths.
Cool conditions are usually required during the first part of the season, when the plants start to
form bulbs. Warm and dry weather is needed for harvesting and curing. Each cultivar differs
in its sensitivity to day-length (Savva and Frenken, 2002).

The onions are grouped into short-days and long-days depending on the day length
requirements. The bulbs that acquire day length of 11.5 hours are categorized into short-day
group and those take 14 hours or more for bulb formation fell into long-day group. Onion also
requires varying day length and temperature for the purpose they produced. A relatively high
temperature and long photoperiod are required for bulb formation, and for seed production,
temperature is of immense importance than day length. Onion bulbs have specific temperature
requirement for seed and bulb production (Baloch, 1994). Light intensity, light quality, and
other factors interact with temperature and day length to influence the bulbing response of
onion cultivars. With warm weather and bright days, onions bulb at shorter day lengths than
when the days are cool and over cast (Hamasaki et al., 1999).

Onion dry bulb are established either by direct sowing to the field, by transplanting seedling or
from dry sets depending on the growing conditions of the specific regions. Sowing seeds
directly into the soil where the crop is to be grown is potentially the most economical method
of raising an onion crop, particularly where the availability of labor for transplanting is limited
and its cost is high or where the availability of facilities for raising transplants is limited
(Brewster, 1994). Sets and transplants are used in areas where the season is not long enough
for proper bulb development. Transplants have the advantage on economic use of seed,
selecting superior (healthy and vigorous) seedlings. It saves weeding and watering effort
during the early weeks of onion growth it enables the farmers attend to the seedlings in a
compact area (Lemma and Shimeles, 2003).
 8

2.3. Importance and Production Status of Onion in Ethiopia

The production of vegetables is becoming important with the expanding irrigated agriculture
and with the growing awareness on the importance of the sector as source of income,
improved food security, sources of raw materials for industries, employment opportunity
because it demands large labor force. The expansion of water harvest schemes in small
farmers sector and irrigated agricultural development projects have made significant
contribution to the development of the sector. The success of production depends on the
adoption of improved technologies such as cultivars that have acceptable standard and high
value in the local use and export markets (Lemma et al., 2006).

Ethiopia has a great potential to produce onion throughout the year both for local
consumption and for export. It grows best at an altitude of between 700-2200 meters above sea
level. Onion is a rapidly becoming popular among producers and consumers. Its popularity
among producers is because of the advantage of high yield potential, availability of desirable
cultivars for various uses, ease of propagation by seed, high domestic (bulb and seed) and
markets in fresh and processed forms (Lemma and Shimeles, 2003). Onion contributes
substantially to the national economy, apart from overcoming local demands. With the
growing irrigate agriculture in the country, there is a great potential for extensive onion seed
and dry bulbs production in the different production belts of the country.

Specifically to onion production and improvement, the Ethiopian Agricultural Research

Institute has made efforts to generate different improved varieties. As a result of this effort the
varieties Adama Red, Bombay Red, Red Creole, Melkam, Mermiru Brown, Nasik Red and
Nafis are made available to farmers (Lemma and Shimelis, 2003; MoARD, 2010). It is widely
produced by small farmers and commercial growers throughout the year for local use and
export market. Onion is important in the daily Ethiopian diet and all the plant parts are edible,
although the bulbs are widely used as a seasoning or a vegetable in various dishes. Onion is
valued for its distinct pungency and form essential ingredients for flavoring varieties of dishes,
sauces, soup, sandwiches, snacks as onion rings etc. It is popular over the local shallot because
 9

of its high yield potential per unit area, availability of desirable cultivars for various uses and
ease of propagation by seed (Lemma, 2004).

Onion is considered as one of the most important vegetable crops produced on large scale in
Ethiopia. It also occupies an economically important place among vegetables in the country.
The area under onion is increasing from time to time mainly due to its high profitability per
unit area and ease of production, and the increases in small scale irrigation areas. The crop is
produced both under rain-fed in the “Meher” season and under irrigation in the off season. In
many areas of the country, the off season crop (under irrigation) constitutes much of the area
under onion production. Despite areas increase, the productivity of onion is much lower than
other African countries. The low productivity could be attributed to the limited availability of
quality seeds and associated production technologies used, among the others (Nikus and
Mulugeta, 2010).

2.4. Response of Onion to Nitrogen Application

2.4.1. Roles of nitrogen in onion nutrition and growth

Onion being among the high nitrogen demanding vegetables, its productivity depends on use
of optimum fertilizer rates and if not adequately fertilized, considerable yield losses are
apparent. Among all nutrients, nitrogen is the most important and also the most limiting to
crop production. Efficient N use is important for the economic sustainability of cropping
systems (Brewster, 1994; Fageria and Baligar, 2005). Excessive use of N fertilizers is a
concern, since large amounts of N can remain in the soil after crop harvesting (Neeteson et al.,
1999). In a temperate climate, usually ≤ 50% of N applied is effectively used by plants, while
a considerable part is lost by leaching and contaminates ground and surface waters (Fageria
and Baligar, 2005).

Mineral fertilizers are one of the principal factors that materially set up onion growth and
production. Onion plants take up large amounts of the three primary nutrients, i.e. nitrogen,
phosphorus and potassium (Kandil et al., 2013). Marschner (1995) also stated that nitrogen
 10

and phosphorus are often referred to as the primary macronutrients because of the large
quantities taken up from the soil relative to other essential nutrients.

2.4.2. Response of onion to nitrogen fertilization

Onion, compared with most crops, is usually the weakest crop plant in terms of extracting
nutrients, especially the immobile types, because of their shallow and unbranched root system
(Brewster, 1994). Thus, the crop is a heavy feeder, requiring ample supplies of N; hence it
requires and often responds well to addition of fertilizers. However, excess application of
nitrogen causes excessive vegetative growth, delayed maturity, increase susceptibility to
diseases, reduces dry matter contents and storability and ultimately reduces yield and quality
of bulbs (Brewster, 1994; Sørensen and Grevsen, 2001).

Soleymani and Shahrajabian (2012) showed that the highest and the lowest marketable yield
were obtained in to the application of 300 kg N ha-1 and 0 kg N ha-1, respectively. Negash et
al. (2009) also reported that increasing the rate of N fertilization from 0 to 138 kg ha-1
increased total bulb yield from 19.26 t ha-1 to 32.24 t ha-1. Similarly, increasing the rate of
nitrogen application from 0 to 138 kg ha-1 significantly increased marketable bulb yield from
18.82 t ha-1 to 31.90 t ha-1 which was 69.5% higher than the control. Jilani et al. (2004)
reported that with increase in dose of nitrogen up to120 kg N ha–1 the marketable and total
bulb yield was increased, but below this level the total yield t ha–1 began to decrease. A
significant increase in total bulb yield in response to nitrogen fertilizer levels was also
observed by (Balemi et al. 2007).

Bolting is triggered in response to exposure of the onion plant to conditions like low
temperature or limited N supply which induces flowers to emerge before bulb are adequately
grown to suppress flower initiation (Yamasaki and Tanaka, 2005). Al-Fraihat (2009) also,
stated that highest percentage of bolting was obtained from plants fertilized with the lowest
level of nitrogen (100 kg N ha-1). Abdissa et al. (2011) also showed that nitrogen fertilization
significantly reduced bolting in onion. The authors reported that ratio of bolting percentage per
 11

plot decreased by about 11 and 22% in response to the fertilization of 69 and 92 kg N ha -1,
respectively as compared to the control.

Yield is composed of marketable and unmarketable dry bulbs. The marketable product
typically depends on onion cultivar (Lemma and Shimeles, 2003). According to the authors,
marketable bulb weight can be grouped into different size of bulb categories: Oversized
(above160 g), large (100-160 g), medium (50-100 g), small (20-50 g) and under-sized below
(20 g). These sizes can be preferred by consumers or users according to their purpose for
planting material, food, as well as for processing. EARO (2004) stated that the different bulb
size category was indicated for different varieties under the Ethiopian conditions: Bombay
Red (85-100 g), Adama Red (60-80 g), Red Creol (80-100 g), Melkam (70-90 g), Mermiru
Brown (70-90 g) and Dereselign (85-100 g). This showed that bulb size category is also highly
dependable on variety in addition to intra-row spacing.

With regard to unmarketable bulb yield of onion, it is related to the under sized bulb which is
below 20 gram, diseased, decayed, physiological disorder such as thick necked, splits and
bolters. Disorders are influenced by location, season, cultivar, and management practice. On
the other hand, thick necked also occurs mainly when some of the proportion of bulbs fail to
complete bulbing in which the leaves continue growing. Under this condition, the neck does
not get soften and the bulb does not become dormant. Heavy and continuous watering and late
application of nitrogen contribute to this disorder (Lemma and Shimeles, 2003). The onion
bulb size increased significantly with the application of different doses of nitrogen.
Application of higher nitrogen of 120 kg ha-1 recorded the maximum bulb size while the
minimum bulb size was recorded in control (Jilani et al., 2009).

Nitrogen significantly affected yields of various onion bulb size categories. Onion fertilized
with different N levels decreased the yield of small sized bulbs, but increased the yield of large
sized bulbs. Small sized bulbs decreased by 61.8% when N application was increased from 0
to 138 kg ha-1. On the hand, when N fertilization increased from 0 to 138 kg ha-1 the increased
large size bulbs increased from 12.58 t ha-1to 25.67 t ha-1, respectively, resulting in 104%
increment (Negash et al., 2009).
 12

Nitrogen fertilization increased the bulb yield of onion and yield components. Increasing
nitrogen levels from 0 to 120 kg ha-1 resulted in progressive increase in bulb yield. Application
of 120 kg N ha-1 increased the number of leaves per plant and plant height over the control as
well as lower levels of nitrogen. There was an increase in diameter and weight of bulbs due to
application of nitrogen up to 120 kg N ha-1 and thereafter decreased (Nasreen et al., 2007). A
report also described by Morsy et al. (2012) indicated that 120 kg N ha-1 appeared higher
values of plant height, number of leaves per plant, bulb diameter and days to maturity as
compared to adding of 90 kg ha-1.

Al-Fraihat (2009) stated that with increasing application of nitrogen fertilizer from 100 kg N
ha-1 to 200 kg N ha-1 in the first and second growing seasons, the TSS value increased from
13.75% to 14.70% and 13.90% to 15.07% during the first and second growing seasons,
respectively. Morsy et al. (2012) also showed application of 120 kg N ha-1 led to the highest
values of TSS whereas, application of 90 kg N ha-1 resulted in the lowest values of TSS in both
seasons. Moursy et al. (2007) also indicated that increasing the level of N fertilizer to 80 kg N
ha-1 resulted in about 8.5% increase in the TSS as compared to the level of 40 kg N ha-1.

The different N levels affected the leaf diameter and length of onion. The application of 150
kg N ha-1 gave the highest value with regard to leaf diameter. Generally, with increasing
nitrogen level from 0 kg ha-1 to 150 kg ha-1 the leaf diameter of onion increased from 0.81 cm
to 1.00 cm (Kokobe et al., 2013). Al-Fraihat (2009) reported the highest level of nitrogen
significantly increased plant height and number of green leaves per plant as compared to the
control treatment.

Nitrogen fertilization significantly extended the number of days required for onion crop to
attain its physiological maturity. Regardless of the rate, N fertilization extended physiological
maturity by about 6 days over the unfertilized treatment (Abdissa et al., 2011). A report by
Meena et al. (2007) also described the delay in maturity of onion bulb due to application of
enhanced level of nitrogen.
 13

Generally, considering the status of the soil, additional nitrogen fertilizer levels application
may be necessary in order to meet the crop N requirements. The amount of N needed is
usually based on soil organic matter content, crop uptake and yield levels. Nitrogen uptake
levels by onion crops may vary from less than 50 kg to more than 300 kg ha-1, depending on
cultivar, climate, plant density, fertilization and yield levels (Soujala et al., 1998).

2.5. Effect of Plant Spacing on Onion Yield and Yield Components

Plant population refers to number of plants per square meter (plants m-2) or hectare (plants ha-
1
) and is important in onion production since it has an influence on growth, yield and quality
of onion bulbs (Brewster, 1994). Plant and row spacing are considered important to the
optimum plant population which may be reflected in higher yield and quality. Onion bulb size
can be controlled to a certain extent by plant population. In order to produce large bulbs (> 70
mm in diameter) a plant population of between 25 and 50 plants m-2 is required, for medium
bulbs (25-50 mm) between 50 and 100 plants m-2 and for small bulbs (< 50 mm) more than
100 plants m-2 are required (Brewster, 1994).

According to Dorcas et al. (2012) reported that with increasing plant density of onion from
lower 100,000 plants ha-1 to higher plant density of 500,000 plants ha-1 then average bulb
weight and bulb diameter decreases from 58.22 g to 40.04 g and 4.56 cm to 2.83 cm
respectively. The authors also reported that highest and lowest yield was obtained in the higher
plant density of 500,000 plants ha-1 and lower plant density of 100,000 plants ha-1. Yemane et
al. (2013) indicated that with increasing intra-row spacing from 5 to 10 cm, statistically bulb
diameter and bulb neck diameter of onion increased from 4.66 to 5.63 cm and 1.48 1.74 cm
respectively. Dawar et al., (2005) indicated that as plant population increased from 40 to 80
plants m-2 onion neck diameter declined significantly. Jilani et al. (2009) indicate that bulbs of
thick neck of onion were found in plots of lowest plant density (20 plants m-2). Bulb neck
diameter decreased as population density increased. Mean bulb weight and plant height
decreased as population density increased (Kantona et al., 2003).

Khan et al. (2002) reported that various plant spacing leads to the increase in plant height,
onion bulb size, and weight of the bulbs, bulbs ha-1 and yield of the bulbs. Khan et al. (2003)
 14

reported that wider spacing (20 x 10 cm) produced higher size of plant height, leaf length and
number of leaves, bulb length, diameter and weight of onion. On the contrary, highest yield
was observed at the closest spacing and the lowest yield at widest spacing. Yamane et al.
(2013) also indicated that as intra-row spacing increased from 5 to 10 cm, marketable bulb
yield in t ha-1 decreased from 34.49 to 28.10. Seck and Baldeh (2009) reported that plant
density has an impact on marketable bulb size and the higher the plant density the smaller the
marketable size. Kantona et al. (2003) also reported that as plant density increased number of
marketable bulbs increased.

Sikder et al. (2010) evaluated three intra-row spacing (20x20, 20x15 and 20 cmx10 cm) of
onion. Based on this, the maximum yield were recorded from 20 cm x 10 cm spacing and the
narrow plant spacing produced comparatively lower values on fresh weight of leaves per plant,
plant height, leaves number per plant, bulb diameter and fresh weight of bulb. Stoffela (1996)
also found that as number of rows per bed increased, marketable onion yield linearly increased
and mean bulb size decreased. Latif et al. (2010) showed that yield of onion bulbs produced at
the spacing of 20 cm x 10 cm was recorded as the highest compared to 20 cm x 20 cm spacing.
Mahadeen, (2008) also reported that narrow intra-row spacing produced higher yield.

According to Balraj et al. (1998) with increase in plant spacing, the bulb weight and size
increased, but the yield ha-1 decreased. Kumar et al. (1998) indicated that the spacing has a
direct effect on the quality and production of onion. Lower planting density was the best with
regard to leaf length. Latif et al. (2010) indicated that the numbers of leaves per plant, bulb
weight, foliage dry weight, plant height was highest when the plants were grown at wider
spacing of 20 x 20 cm. However, yield per unit area was higher in the narrow spacing. Nasir et
al. (2007) also stated that the highest leaf number per plant was recorded at lower planting
density. Planting of onion at 20 and 25 cm spacing produced larger bulbs compared with
planting at 10 and 15 cm spacing (Mahadeen, 2008). Jilani (2004) reported that onion plants
from the lowest plant population (20 plants m-2) recorded the highest number of leaves and
leaf length.
 15

According to Jan et al. (2003), the highest yield (40.44 t ha-1) was found at spacing of 17 x 4.5
cm, and the lowest yield (19.95 t ha-1) at 27 x 14.5 cm spacing. Yemane et al. (2013) also
indicated that the highest total bulb yields were achieved at 5 and 7.5 cm intra-row spacing,
respectively as compared to the 10 cm intra-row spacing. Dereje et al. (2012) also indicated
that total yield per hectare increased as plant density increased although yield of the individual
plants and their components were significantly reduced suggesting a compensation of higher
plant densities on yield in shallot.

Kantona et al. (2003) observed that onion yield increased from 17.4 to 39.5 t ha-1 as plant
population per square meter increased from 50 to 150. Yemane et al. (2013) mentioned that
the highest unmarketable bulb yield of onion was produced by the narrow intra-row spacing.
Dereje et al. (2012) also reported that high unmarketable yield of shallot was recorded in
closely spaced plants. Seck and Baldeh (2009) also concluded that plant density has an impact
on marketable bulb size. The smaller the marketable size is an issue for high plant densities
and needs to be improved.

According to Nasir et al. (2007) maximum weight of small and medium sized of onion was
obtained at higher population density, However, the highest weights of large bulbs were found
at the lowest planting density. Dawar et al. (2007) also reported that maximum weight of
medium and small sized bulb was achieved at higher planting density of 80 plants 4m-2.
However, maximum weight of large bulbs was found at the lowest planting density of 40
plants 4m-2. Rumpel et al. (2000) showed that yield of medium bulbs increased with density
but, the yield of large bulbs decreased as plant density increased. Stoffella (1996) also
mentioned that percentage of small and medium sized bulbs increased and percentage of large
bulbs decreased as intra-row spacing decreased. Yemane et al. (2013) stated that the highest
percentage of small and medium size bulbs yield was scored at narrow intra-row spacing of 5
cm as compared to 7.5 cm and 10 cm. However, as the intra-row spacing increased from 5 to
10 cm, the percentage of large size bulbs increased from 9.3 to 20.3%.

Minimum planting density attained the highest number of leaves which decreased with
increasing planting density. Minimum plant population (20 plants m-2) had larger bulb
 16

diameter against smaller bulb diameter of higher plants density (40 plants m-2) (Jilani et al.,
2009). A report by Hyder et al. (2007) who indicated that plant height, bulb length, bulb
diameter and days to harvest were the most important yield contributing factors. There is
indirect effect on bulb yield of each trait. Plant height revealed a positive indirect effect on
yield and was favorable through bulb length, bulb neck thickness, TSS in Brix and dry matter
content. Akoun (2005) reported that bulb diameter was greatest (8.18cm) at the lowest
population density. Seid et al. (2014) indicated that lowest leaf width (0.73 cm) of garlic was
recorded in higher plant density.

Bosch and Olivé (1999) in Spain conducted two experiments, one under natural light condition
and another one under black neutral shade, with the aim of investigating an influence of plant
population (20, 40, 80 and 160 plants m-2) on bolting percentage using a long day cultivar.
Based on this, under natural light condition, as plant population increased from 20 to 160
plants m-2, number of bolters significantly increased from 8 to 75.

Onions have a high harvest index with 70 to 80% of the shoot dry weight found in the bulb at
maturity. As compared to other crops, onions are poor at intercepting radiation, average at
converting radiation to dry matter but good at partitioning the dry matter to harvestable
material (Brewster, 1990). Dereje et al. (2012) reported that lower harvest index of shallot in
wider intra-row spacing. Kabir and Sarkar (2008) also reported highest value of harvest index
of mungbean recorded from closer spacing probably due to the reduced vegetative biomass.

The ideal spacing and plant population are those that maximize yield, vegetable quality and
profits to farmers without excessively increasing costs. An essential aspect of any crop
production system is the development of a crop canopy that optimizes the interception of light,
photosynthesis, and the allocation of dry matter to harvestable parts. A crop canopy is
commonly managed by manipulating row spacing and plant population; as plant density
increases, yield per unit area will approach an upper limit, plateau, and then decline while
yield per plant tend to decrease with increasing plant density because of competition for
growth factors between adjacent plants (Silvertooth, 2001).
 17

Generally, yield of onion increases with an increase in plant population because plant densities
allowed the canopy to close quickly reducing the ability of weeds to compete, but only up to
an optimal limit and yield will decrease beyond this optimum. Appropriate spacing enables the
farmers to keep appropriate plant population in their field. Hence, a farmer can avoid over and
less population in a given plot of land, which has negative effect on yield. Therefore, to avoid
nutrient competition due to inappropriate use of plant spacing and N fertilizer, sufficient
spacing between plants and rows and optimum amount N fertilizer application is vital to get
highest yield in a given plot of land (AVRDC, 2004).

2.6. Response of Onion to Interaction Effect of Nitrogen and Plant Spacing

Islam et al. (1999) reported that interaction effect of spacing and N levels on bulb yield of
onion and most of the characters. The highest spacing in association with high nitrogen level
up to 180 kg ha-1 increased number of leaves per plant and splitted bulbs. The highest bulb
yield (31.6 t ha-1) was obtained from the lowest spacing (20x10 cm) along with nitrogen level
of 120 kg ha-1 but the large sized bulbs were obtained from the combination of higher spacing
(20 x 20 cm) and at 120 kg N ha-1.

According to Naik and Hosamani (2003) the narrow spacing of 15 x 10 cm gave the maximum
bulb yield of onion and decreased the bulb yield with widening spacing. The highest bulb
yield was recorded with treatment interaction of closer spacing (15 x 10 cm) and higher levels
of nitrogen (150 kg ha-1). The bulb diameter was highest in the wider spaced crop (15 x 20 cm)
followed by 15 x 15 cm than narrow spacing. Similarly, this parameter was also increased with
increase in nitrogen levels and the bigger sized bulbs were found in the plots applied with 150
kg N ha-1. Average bulb weight was increased with increase in nitrogen levels. The highest
bulb weight was found in the plots applied with 150 kg N ha-1 (Naik and Hosamani, 2003).
The TSS was increased with increase in nitrogen levels and the maximum (10.15%) was
recorded in the bulbs applied with 150 kg N ha-1 followed by 100 kg N ha-1 (9.15%). Shojaei et
al. (2011) also reported that the highest mean bulb weight was produced by the plants treated
with higher nitrogen and lower population density. The increase in N fertilization level and
plant population also resulted in the increase in yield from 3 to 10 t ha-1.
 18

Maximum number of leaves per plant was produced by the treatment interaction of higher
nitrogen (150 kg N ha-1) with wider (15 cm spacing). Mean values of root diameter in response
to different nitrogen levels showed superiority in 200 kg N ha-1 over 100 kg N ha-1 and 0 kg N
ha-1. It would be observed from the means of interactions that 200 kg ha-1 with 10 cm spacing
produced maximum root yield per hectare. Nitrogen dose of 200 kg ha-1 when interacted with
15 cm spacing produced maximum total biomass per plant followed by 200 kg N ha-1 with 10
cm spacing (Pervez et al. 2004).

Interaction effect of different intra-row spacing (10, 15, 20 and 25 cm) and levels of nitrogen
fertilizer (0, 50, 100 and 150 kg N ha-1) showed that an increase in nitrogen dose up to 100 kg
ha-1 resulted in the increase of yield of onion bulbs 40.83 t ha-1 by interacting with 15 cm intra-
row spacing. But, further increase in N level up to 150 kg ha-1 did not significantly increase in
bulb yield. The lowest bulb yield was recorded from the control plots when interacted with
wider intra-row spacing of 25 cm (Aliyu et al., 2008). The authors reported that treatment
combinations of 0 kg N ha-1 and 10 cm intra-row spacing gave lower values of average bulb
weight, bulb diameter and leaves number per plant.
 19

3. MATERIALS AND METHODS

3.1.Description of the Study Area

The experiment was conducted at Axum Agricultural Research Center (AxARC) which is
located at 5 km away from Axum city in a westerly direction and a distance of about 245 away
from Mekelle city in the north-western direction. The study site is located at Dura in La’elay
Maichew Woreda, Central Zone of Tigray. It is situated at the latitude of 46o35’ 31’’ N and
longitude of 55o 96’ 22” E with an altitude of 2042 meters above sea level in the semi-arid
tropical belt of Ethiopia with “Weina dega” agro climatic zone. The rainy season is mono-
modal concentrated in one season from July to September, with an average rain fall of 700 –
800 mm. The mean minimum and maximum temperature ranges from 8.70C to13.20C and
24.40C to 31.40C, respectively.

Figure 1. Map of the Study Area

 20

3.2. Experimental Materials

3.2.1. Planting material

‘Bombay red’ onion variety was used for the study. Seeds for planting were obtained from
Axum Agricultural Research Center (AxARC). The variety was released by Melkassa
Agricultural Research Center in 1980 (EARO, 2004). The variety has light red bulb skin color,
dark green leaf color, flat globe bulb shape and reddish white bulb flesh color. The variety
takes 110-120 days for bulb harvest (EARO, 2004). Bombay red is one of the most commonly
and widely used improved variety in Central Zone Tigray in particular and in the region in
general.

3.2.2. Fertilizer material

The sources of the fertilizers were urea (46% N) and Triple Super Phosphate, TSP (46% P 2O5)
for supplying nitrogen and phosphorus, respectively

3.3. Treatments and Experimental Design

The treatments consisted of five intra-row spacing (2.5, 5, 7.5, 10 and 12.5 cm) and four levels
of nitrogen (0, 41, 82 and 123 kg N ha-1). The experiment was laid out as a randomized
complete block design (RCBD) with three replications. Each treatment was assigned to the
plots randomly. Onion seedlings were planted in double row spacing. The spacing between
furrows was kept at 60 cm and the spacing between the double rows in a furrow was 20 cm.
 21

Table 1: Treatment combinations, number of plants m-2, number of plants per plot and plant
population per hectare

Treatment Nitrogen Intra-row Equivalent Number of Number of Number

combinations rates kg N spacing area (m2) plants m-2 plants plot- of plants
ha-1 (cm) 1
ha-1
(T1) = N1 S1 0 1333333
(T2) = N2 S1 41 1333333
(T3) = N3 S1 82 2.5 0.0075 133.33 672 1333333
(T4) = N4 S1 123 1333333
(T5) = N1 S2 0 666667
(T6) = N2 S2 41 666667
(T7) = N3 S2 82 5 0.015 66.67 336 666667
(T8) = N4 S2 123 666667
(T9) = N1 S3 0 444444
(T10)=N2S3 41 224 444444
7.5 0.0225 44.44
(T11) = N3S3 82 444444
(T12) = N4S3 123 444444
(T13) = N1S4 0 333333
(T14) = N2S4 41 333333
(T15) = N3S4 82 10 0.03 33.33 168 333333
(T16) = N4S4 123 333333
(T17) = N1S5 0 266667
(T18) = N2 S5 41 266667
12.5 0.0375 26.67 134
(T19) = N3 S5 82 266667

(T20) = N4 S5 123 266667

Where N1=0 kg N ha-1, N2= 41 kg N ha-1, N3=82 kg N ha-1, N4=123 kg N ha-1 and S1=2.5
cm, S2=5 cm, S3=7.5 cm, S4=10 cm and S5=12.5 cm intra-row spacing

3.4. Management of Experimental Field

Seeds were sown in a nursery on well prepared seed bed in the first week of October 2014.
When seedlings attained proper stage for transplanting at 3 or 4 leaves stage estimated around
 22

12 to 15 cm height, was transplanted to the experimental field. Seedlings were planted on fine
soil which was prepared following the recommended tillage practice for the crop. Each
treatment combination was assigned randomly to experimental units within a block. Each
experimental plot had eight single rows. During data collection the middle six single rows
were considered for recording all data excluding the two border rows as well as those plants at
both ends of each row to avoid edge effects.

Planting was done on ridges of the furrow adopting recommended spacing of 40 cm between
furrows, 20 cm between rows on the ridge. A 2.1m x 2.4 m (5.04 m2) plot size was used for
each experimental unit. The blocks were separated by 1.5 m width whereas the space between
each plot within a block was 1 m. Triple super phosphates (46% P2O5) was applied as a source
of P in the rate of 92 kg P2O5 for all plots uniformly. The nitrogen source was Urea (46% N).
All TSP fertilizer was applied at planting as a single application (92 kg P2O5 ha-1) and
incorporated to the soil on the prepared ridges in bands. Nitrogen was side dressed in two
splits of equal amounts after 3 and 6 weeks of transplanting. Plots were supplemented with
irrigation at field capacity depending on the moisture condition of the soil and soil type.
Weeding and hoeing was done manually by hand weeding and hoeing. The crop was harvested
when 80% of the leaves turned yellow and top fall, attaining full size of bulbs and then cured
for a day.

3.5. Soil Sampling and Analysis

The soil sample taken from the experimental site was done in Mekelle soil laboratory. Soil
samples were collected randomly from the entire experimental field following a zigzag fashion
from 0 to 30 cm depth before planting using an augur. The soil samples were collected from
the entire experimental field and it was made one kg composite sample. Determinations of
some selected soil chemical properties were carried out based on the composite sample. The
composite soil sample was air dried, crushed with wooden pestle and mortar to pass through a
2 mm sieve size for the analysis of physical and chemical properties. Total nitrogen, available
phosphorus, potassium, organic matter, soil pH, cation exchange capacity (CEC) and soil
texture was determined in the laboratory from the sample submitted.
 23

Soil pH was measured in 1:2.5 soil-water ratios using an electrodes pH meter. Organic carbon
content of the soil was determined by Walkley and Black method (Walkley and Black, 1934).
Available phosphorus was estimated following the standard procedure of Olsen et al., (1954).
Total nitrogen was estimated by the Kjeldahl method (Jackson, 1958). The results of the soil
analysis were used as inputs in determining the applied amount of nitrogen fertilizer and to
know the suitability of the selected site for onion production during experimental period.

3.6. Data Collection

Data on growth, yield and yield components of onion were recorded from the six central
double rows plants which were selected randomly in each plot as specified in each plant
characters below. However, data for phenology of crop was collected from the entire plot.

3.6.1. Phenology and growth parameters

Stand count (% tage): plants that successfully established in the central rows were counted at
harvest and expressed as percentage.

Days to maturity: The number of days from seedling transplanting to a day at which more
than 80% of the plants in a plot showed yellowing of leaves or attained physiological maturity.

Plant height (cm): This was measured from the ground to the tip of the leaves from 10
randomly selected plants at maturity.

Leaf number per plant: The total number of leaves per plant was counted from 10 randomly
selected plants at maturity.

Leaf diameter (cm): The diameter of leaves at three different places of the leaves was
measured from ten randomly selected plants using veneer calliper.
Bolting percentage: Each experimental plot was examined regularly. Plants showing flower
escapes during vegetative growth was counted and calculated as the ratio of bolters per total
plants in the plot and the values was expressed in percentage.
 24

Leaf Length (cm): This was measured at physiological maturity from the sheath to tip of the
leaf from the ten leaves of the representative plants which was used to count the number of
leaves per plant using a ruler.

Shoot dry matter (g): This refers to the above ground biomass of the plant, which was oven-
dried at the temperature of 65 0C until a constant weight was obtained. The aboveground
biomass was harvested by cutting the plant at the crown part and the shoot dry matter was
determined and expressed in gram at harvest.
Dry total biomass (g): This was determined by summation of the shoot and bulb dry weights
of sample plants.

3.6.2. Yield and yield components

Bulb diameter (cm): The mean bulb diameter of ten sample bulbs was measured at the
maximum wider portion of matured bulbs using calipers.

Neck diameter (cm): The average neck widths of ten randomly taken mature bulbs was
measured by using a veneer calliper and expressed in centimetre after harvest.

Average bulb weight (g): The average fresh weight of ten randomly taken mature bulbs
measured by using sensitive balance and finally then expressed in grams

Bulb dry matter (g): Five bulbs were randomly taken from each plot and chopped into small
1-2 cm cubes, mixed thoroughly, and two sub-samples each weighing 200 gram was weighed.
The exact weight of each sub-sample was determined and recorded as fresh weight. Each sub-
sample was placed in a paper bag and put in an oven until constant dry matter was attained.
Each sub-sample was then immediately weighed and recorded as dry matter yield.

Marketable bulb yield (t ha-1): This referred to the weight of healthy and marketable bulbs
that range from 20 g to 160 g in weight. Bulbs below 20 g in weight were considered too small
to be marketed whereas those above 160 g were considered oversized according to Lemma and
Shimeles (2003). This parameter was determined from the net plot at final harvest and
expressed as t ha-1.
 25

Unmarketable bulb yield (t ha-1): The total weight of unmarketable bulbs that are under
sized (< 20 g), diseased, decayed and bulbs from plants with physiological disorder such as
thick neck and split was measured from a net plot at final harvest and expressed in t ha-1.

Bulb size distribution of marketable bulbs: Based on the weight of bulbs from categories of
bulb size for small (20 - 50 g), medium (50 – 100 g), large (100 -160 g), and oversized (> 160
g) was recorded per net plot and converted to t ha-1 as determined by Lemma and Shimeles
(2003).

Undersized bulb yield (t ha-1): Under sized bulbs (< 20 g) was recorded as unmarketable
bulbs per net plot and converted to t ha-1 as determined by Lemma and Shimeles (2003).

Total bulb yield (t ha-1): The total bulb yield was measured from the total harvest of net plot
as a sum weight of marketable and unmarketable yields that was measured in kg per plot and
finally converted into t ha-1.

Harvest index (%): This was expressed as the ratio of total bulb dry weight to the total
biomass dry weight and expressed in percentage.

Total bulb dry weight

Harvest index (HI) = x100
Total biomass dry weight
Total soluble solid (0Brix): The TSS was determined at harvesting time from ten randomly
selected bulbs using the procedures described by Waskar et al. (1999). Aliquot juice was
extracted using a juice extractor and 50 ml of the slurry centrifuged for 15 minutes. The TSS
was determined by a hand refractometer (ATAGO TC-1E) with a range of 0 to 32 0Brix and
resolutions of 0.20 Brix by placing 1 to 2 drops of clear juice on the prism, washed with
distilled water, and dried with tissue paper before use.
 26

3.7. Data Analysis

The data were subjected to analysis of variance (ANOVA) using SAS version 9.1.3 computer
software (SAS Institute Inc., 2004). Duncan Multiple Range Test (DMRT) was used to
separate and compare treatment means at 5% probability level. Correlation analysis was
computed to generate information about the association of yield and other parameters.
 27

4. RESULTS AND DISCUSSION

4.1. Physico-Chemical Properties of the Experimental soil

The results of the soil analysis are presented in Table 2. The mean pH value was 7.48, which is
slightly alkaline according to the rating of Murphy (1968). The optimum pH for onion
production ranges between 6 and 8 (Nikus and Mulugeta, 2010). Accordingly, the pH of the
soil was conducive for onion production. The organic carbons as well as that of total nitrogen
contents of the soil were medium according to the rating of Tekalign (1991). This shows that
the soil was moderate in supplying organic carbon for soil biota and also as a source of
mineralized nitrogen for uptake mineral nitrogen by crops (Hazelton and Murphy, 2007).
Hence, it requires application of nitrogen for onion production. According to Olsen et al.
(1954), the soil of the experimental site was medium in available phosphorus. This shows that
application of external source of phosphorus is important for growing onions. According to the
rating of Hazelton and Murphy (2007), the soil of the experimental site had medium
exchangeable potassium content, which is adequate for onion production and the total cation
exchange capacity of the testing site was high.

Table 2: Chemical characteristics of the experimental soil

Soil Properties Values Rating Source
pH 7.48 Slightly Murphy (1968)
alkaline
Organic carbon (%) 1.65 Medium Tekalign (1991)
Total nitrogen (%) 0.109 Medium Tekalign (1991)
Total Available phosphorus (mg/kg) 8.16 Medium Olsen et al. (1954)
Total available potassium (cmol (+)/kg) 0.38 Medium Hazelton and Murphy (2007)
Cation exchange capacity (cmol (+)/kg) 35.6 High Hazelton and Murphy (2007)
Electrical conductivity (ds /m) 0.15 Non saline Hazelton and Murphy (2007)
Particle size distribution
Sand (%) 19
Silt (%) 21
Clay (%) 60
Textural class Clay Hazelton and Murphy (2007)
 28

4.2. Phenology and Growth Characters

4.2.1. Plant height

Result from the analysis of variance revealed that the main effects of nitrogen and intra-row
spacing significantly (P < 0.01) influenced plant height of onion. However, the two factors did
not interact to influence plant height (Appendix Table 1).

Increasing the intra-row spacing from 2.5 to 5.0 cm increased plant height significantly.
Increasing the plant spacing further from 5.0 to 7.5 cm also increased the height of onion
plants significantly whereas; the increase in plant spacing further from 7.5 cm to 12.5 cm did
not show significant difference. Thus, the heights of onion plants grown at the spacing of 7.5
cm exceeded the heights of onion plants grown at the spacing of 2.5 and 5.0 cm by about 7%
and 15%, respectively. Similarly, increasing the rate of nitrogen from nil to 41 kg N ha -1
significantly increased the height of onion. Increasing the rate of nitrogen further from 41 to
82 kg ha-1 also increased the height of onion plants. But, the mean height of plant did not show
significant difference as further increase in nitrogen rate from 82 to 123 kg ha-1. Thus, the
mean height of onion treated with nitrogen at the rate of 82 kg ha-1 exceeded the height of
onion plants treated with nil and 41 kg N ha-1 by about 28 and 16%, respectively.

The increase in plant height at the medium intra-row spacing may be due to less interplant
competition for the growth factors like water, nutrient and light, which may lead to better
growth and significantly taller plant height as compared to narrow intra-row as explained by
Khan et al. (2002). However, widening the spacing beyond the 7.5 cm threshold did not
change plant height, indicating that too much widening of the spacing beyond the potential of
the plant would have no added value for growth. This finding agrees with results of Khan et al.
(2003), Kantona et al. (2003) and Aliyu et al. (2008), who reported that wider rather than
narrower spacing produced taller onion plants, showing that narrower spacing leads to stiffer
competition among plants for growth factors, causing reduced growth. Corroborating the
results of this study, Hamma et al. (2013) also showed that plant heights of garlic plants
increased in response to increasing intra-row spacing.
 29

The increase in plant height with the addition of higher nitrogen fertilizer level could be
attributed to more availability of the nutrient which enhances protein synthesis which lead to
increased accumulation of carbohydrates and this in turn, may have resulted in increased plant
growth such as leaf number and leaf length (Rizk, 2012; Marschner, 1995). This result is
consistent with the findings of Morsy et al. (2012), Nasreen et al. (2007) and Al-Fraihat
(2009) who reported that onion plant height significantly increased as nitrogen fertilizer rates
increased.

Table 3: Main effect of intra-row spacing and nitrogen fertilizer levels on plant height of onion

Treatment Plant height (cm)

Intra-row spacing (cm)
2.5 38.08c
5 41.04b
7.5 43.78a
10 44.85a
12.5 45.27a

Nitrogen fertilizer (kg N ha-1)

0 36.56c
41 40.30b
82 46.70a
123 46.85a
SE(±) 1.72
CV (%) 6.98
Means followed by the same letter in the same column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Test

4.2.2. Leaf number per plant

The analysis of variance revealed that main effect of intra-row spacing and nitrogen fertilizer
rates and their interaction effect had significant (P < 0.01) effects on the number of leaves per
plant of onion (Appendix Table 1).

Increasing plant spacing significantly increased onion leaf number per plant across the
increasing rate of the nitrogen fertilizer. Thus, plants with the highest leaf number were
produced in response to application of the highest rate of nitrogen fertilizer (123 kg ha-1) at the
widest intra-row spacing (12.5 cm). On the other hand, plants with the lowest number of
 30

leaves per plant were produced in response to the narrowest intra-row spacing (2.5 cm) and all
rates of the nitrogen fertilizer as well as at nil rate of the nitrogen fertilizer and the intra-row
spacing of 5.0 cm. For example, the number of leaves of onion plants grown at the intra-row
spacing of 12.5 cm and nitrogen rate of 123 kg N ha-1 exceeded the leaf number of onion
plants grown at the intra-row spacing of 2.5 cm and nitrogen rate of nil kg N ha-1 by about
110% (Table 4).

The maximum number of leaves per plant of onion obtained in treatment combination of wider
(12.5 cm) intra-row spacing and higher nitrogen fertilization (123 kg N ha-1) might be due to
nitrogen mainly related to production of new shoots and vigor in vegetative growth of plants
which is directly responsible for increasing leaf number as described by Rizk (2012) and
Kokobe et al. (2013). Thus, there is less competition for nutrients, moisture and light among
the plants to achieve the required food for their growth due to the wider intra-row spacing.

This result is concordant with the findings of Rao et al. (2013) who reported that highest leaf
number per plant of onion was recorded with the highest combination of 75 kg N ha-1 and 20
cm x 12.50 cm spacing. Consistent with the results of this study, Khan et al. (2002) also
indicated that lower leaf number per plant of onion was recorded from the treatment
interaction effect of control nitrogen level and narrow intra-row spacing. Dawar et al. (2007),
Latif et al. (2010), Sikder et al. (2010), Kumar et al. (1998) and Jilani et al. (2009) also
showed that higher leaf numbers per plant of onion were recorded in response to wider plant
spacing.

4.2.3. Leaf length

Onion leaf length was significantly (P < 0.01) influenced by the main effects of both plant
spacing and nitrogen application as well as by their interaction (Appendix Table 1).

With widening the intra-row spacing, leaf length of onion plants increased significantly across
the increasing rate of the nitrogen fertilizer. Hence, plants treated with nitrogen at the rates of
82 and 123 kg N ha-1 and spaced at 5.0, 7.5, 10.0, and 12.5 cm produced the longest leaves.
However, plants treated with nil and 41 kg N ha-1 and spaced 2.5 cm apart as well as those
 31

treated with nil kg N ha-1 and spaced 5.0 cm apart produced the shortest leaf length. The
shorter value of leaf length of onion found in treatment combination of nil N ha-1 and 2.5 cm
intra-row spacing decreases by about 36% as compared with the highest value of leaf length of
onion achieved in treatment interaction of higher nitrogen rate (123 kg ha-1) and wider spacing
(12.5 cm) (Table 4).

The reasons for longer leaf length of onion with combination of widening intra-row spacing
and increasing nitrogen fertilizer level might be due to nitrogen is a constituent of many
fundamental cell components and plays a vital role in cell division and elongation in plants. It
improves the vegetative growth of the onion which leads to increasing in leaf length through
the increased photosynthetic area in response to nitrogen fertilization that enhanced assimilates
production and partitioning to the plants (Bungard et al.,1999). The results of this study are in
accord with those of Abdissa et al. (2011), Jilani et al. (2004) and Rao et al. (2013) who
reported that higher nitrogen fertilization increased leaf length of onion. Likewise, Kumar et
al. (1998), Khan et al. (2003), Khan et al. (2002) and Jilani et al. (2010) reported that wider
intra-row spacing significantly increased leaf length of onion.

4.2.4. Leaf diameter

The main effects of nitrogen as well as intra-row spacing significantly (P < 0.01) influenced
leaf diameter of onion. Similarly, the two factors also interacted to influence significantly (P <
0.01) leaf parameter (Appendix Table 1).

Almost similar to the effect observed on leaf length, with increase in the intra-row spacing,
leaf diameter of the onion plants increased significantly across the increasing rate of the
nitrogen fertilizer. Thus, plants treated with nitrogen at the rates of 123 kg N ha-1 and spaced
12.5 cm produced leaves with the widest diameter. However, plants treated with nil kg N ha-1
and spaced 2.5 cm apart produced leaves with the narrowest diameter. Thus, the leaf diameter
of onion plants treated with 123 kg N ha-1 and spaced at 12.5 cm intra-row spacing increased
by 194% as compared to the leaf diameter of onion plants treated with no nitrogen fertilizer
and spaced 2.5 cm (Table 4).
 32

The increase in leaf diameter with the increase in the rate of nitrogen and intra-row spacing
could be associated with better supply of nitrogen and less stiff competition for other growth
factors among the onion plants. Thus, more widely spaced plants with higher supply of
nitrogen are able to intercept more light and capture other resources for photosynthesis and
better growth and development. Concurrent with the results of this study, Seid et al. (2014)
and Yemane et al. (2013) also showed that the lowest leaf diameter was recorded for narrow
intra-row spacing of garlic and onion respectively. Supporting the current finding, Abdissa et
al. (2011) and Kokobe et al. (2013) reported that that the smallest onion leaf diameter was
recorded for the nil nitrogen rate.

4.2.5. Shoot dry matter yield

The analysis of variance revealed that the main effects of nitrogen application and intra-row
spacing significantly (P < 0.01) influenced shoot dry matter yield of the onion plants. The
interaction effect of nitrogen application and intra-row spacing also significantly influenced
the shoot dry matter yield of the crop (Appendix Table 4).

With decreasing population density, shoot dry matter yield per plant of onion significantly
increased across the different rates of nitrogen application. Thus, intra-row spacing of 12.5 cm
and nitrogen fertilizer rate of 123 kg ha-1 was the treatment combination at which the highest
shoot dry matter yield was attained. On the other hand, the lowest shoot dry matter yield was
recorded for onion plants spaced at 2.5 cm intra-row spacing that received the nitrogen rates of
0 kg ha-1 and 41 kg ha-1. For example, comparing the onion shoot dry matter yields, the
treatment combination 123 kg N ha-1 and 12.5 cm increased the shoot dry matter yield by
342% as compared to the narrow intra-row spacing of 2.5 cm and nil nitrogen fertilizer
application.

The higher onion shoot dry matter yields were recorded at wider intra-row spacing and higher
nitrogen rates might be linked to nitrogen increases or enhances assimilate production in onion
plants (Sharma, 1992). The plant grown at the widest spacing produced the highest shoot dry
matter yield might also be attributed to the less stiff competition among onion plants for
growth factors, as a result more accumulation of dry matter may have occurred. The present
 33

finding is in agreement with the results of Nasreen et al. (2007) who indicated that higher
shoot dry weight was obtained when the rate of nitrogen fertilizer was increased from 0 kg N
ha-1 to 150 kg ha-1. Rao et al. (2013) also stated that the maximum weight of leaves per plant
was recorded with the application of nitrogen at the higher rate of 75 kg ha-1 and wider spacing
of 20 x 12.5 cm. Consistent with this results Yemane et al. (2014) showed that leaf dry matter
yield of onion decreased from 2.63 to 1.48 g per plant in response to increasing planting
densities.

Table 4: Interaction effect of intra-row spacing and nitrogen fertilizer levels on leaf number
per plant, leaf length, leaf diameter and shoot dry matter yield of onion

Intra-row Parameters
spacing
N level (kg (cm) Leaf number Leaf length Leaf Shoot dry
ha-1) per plant (cm) diameter matter
(cm) (g plant-1)
0 2.5 6.60h 23.00g 0.470l 0.73l
5 6.90gh 25.47fg 0.590k 0.86jk
7.5 7.53fg 27.13ef 0.682ij 0.92jk
10 7.63fg 27.27ef 0.707i 1.26i
12.5 7.70fg 28.40def 0.783h 1.56h
41 2.5 6.43h 25.00fg 0.570k 0.81kl
5 7.57fg 28.23def 0.693ij 1.25i
7.5 8.53ef 28.67def 0.838g 1.56h
10 8.93e 28.83def 0.980e 1.70g
12.5 9.33de 30.00cde 1.057d 2.20d
82 2.5 6.83gh 29.03def 0.643j 0.97j
5 9.96cd 33.23abc 0.920f 1.71g
7.5 10.00cd 34.23ab 1.00cd 2.07e
10 10.40cd 34.33ab 1.117c 2.70c
12.5 10.53bc 34.53ab 1.210b 2.96b
123 2.5 7.03gh 31.40b-e 0.783h 0.97j
5 10.06cd 31.67a-d 0.957ef 1.87f
7.5 10.33cd 33.30abc 1.097cd 2.28d
10 11.47b 35.53ab 1.190b 2.96b
12.5 12.57a 35.87a 1.380a 3.22a
CV (%) 6.62 4.38 3.31 4.27
SE (±) 0.34 0.77 0.02 0.04
Means followed by the same letter with in a column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests
 34

4.2.6. Dry total biomass yield

The main effect of intra-row spacing and that of nitrogen as well as the interaction effect of the
two factors significantly (P < 0.01) influenced dry total biomass yield (Appendix Table 4).

With the increase in intra-row spacing, dry total biomass yield of the onion plants increased
significantly across the increasing rate of the nitrogen fertilizer. Thus, plants treated with
nitrogen at the rates 123 kg N ha-1 and spaced at 12.5 cm intra-row spacing produced the
highest dry total biomass yield. However, plants treated with nil kg N ha-1 and spaced 2.5 cm
apart produced the lowest dry total biomass yield. Thus, the total dry biomass yield obtained
from plants treated with the combination of 123 kg N ha-1 and intra-row spacing of 12.5 cm
was about 6.5 fold higher than the total dry biomass yield produced by onion plants treated
with no nitrogen fertilizer and spaced 2.5 cm apart (Table 5).

The increase in total dry biomass yield in response to the increasing rate of nitrogen fertilizer
and wider intra-row spacing may be probably associated with the nitrogen supply, which
enhances the vegetative growth of plants like leaf number, leaf diameter, leaf length and plant
height which contribute for improved rate of photosynthesis and assimilate production in the
vegetative part and partitioning to the bulbs (Sharma, 1992). In addition, plants grown at the
widest spacing produced the highest dry total biomass yield possibly due to less competition
among them for growth resources.

Supporting the current study, Sikder et al. (2010) reported that higher values of shoot and bulb
dry weight leads to higher in dry total biomass of onion in wider spacing. Similarly, Nasreen
et al. (2007) and El-Tantawy and El-Beik (2009) indicated that application of higher N doses
ha-1 increased dry total biomass yields of onion. In harmony with the results of this study,
Pervez et al. (2004) indicated that maximum total biomass per plant of radish was obtained in
response to the application of higher nitrogen doses interacting with wider intra-row spacing
of radish.
 35

4.2.7. Days to maturity

The result of the analysis of variance indicated that days to maturity was significantly (P <
0.01) affected by the interaction effect of intra-row spacing and nitrogen fertilizer rate.
Moreover, the main effect of intra-row spacing also revealed significant (P <0.01) effect on
days to maturity (Appendix Table 4).

Increasing the rate of nitrogen markedly prolonged the days to maturity of the onion crop
across the increasing intra-row spacing. Thus, plants grown at the higher rates of nitrogen
application and the wider intra-row spacing required progressively more number of days to
mature than plants that were supplied with the lower rates of nitrogen and narrower intra-row
spacing. For instance, onion plants grown at 82 and 123 kg N ha-1 at the spacing of 12.5 cm as
well as those grown at the rate of 123 kg N ha-1 at the spacing of 10 cm required the highest
number of days to reach maturity. In contrast, the lowest number of days to reach maturity was
required by onion plants grown at nil and 41 kg N ha-1 spaced 2.5 cm between plants as well
as those grown at nil rate of nitrogen fertilizer spaced with 5.0 cm between plants. For
example, the days to maturity required by plants grown at the rate of 123 kg N ha-1 and intra-
row spacing of 12.5 cm exceeded the days to maturity required by plants grown in the control
treatment by about 27% (Table 5).

The delay in maturity in response to the increased rate of nitrogen application and wider intra-
row spacing may be attributed to nitrogen enhancing plant biochemical processes, which in
turn extends vegetative growth as a result of which it leads to delayed maturity (Brewester,
1994; Marschner, 1995). This result is consistent with the findings of Abdissa et al. (2011),
Meena et al. (2007) and Morsy et al. (2012) who reported that maturity of onion plants was
delayed in response to increasing nitrogen application. In agreement with the result of this
study, Brewster (1994) and Sørensen and Grevsen (2001) reported that ample nitrogen supply
could result in excessive vegetative growth and delayed maturity of onion.
 36

4.2.8. Bolting percentage

The main effect of nitrogen and intra-row spacing significantly (P < 0.01) affected the bolting
percentage of onion. Moreover, the two factors interacted to influence this parameter
significantly (P < 0.01) (Appendix Table 1).

Bolting percentage of the onion plants significantly decreased with increasing rate of nitrogen
application across the increasing intra-row spacing between plants. Thus, the highest bolting
percentages were recorded for plants grown at nil rates of nitrogen and intra-row spacing of
2.5 and 5.0 cm. However, the lowest bolting percentages were recorded for onion plants
grown at the rates of 82 and 123 kg N ha-1 and intra-row spacing of 10 and 12.5 cm (Table 5).

The increase in bolting percentage in response to the lower rates of N application as well as
the narrower intra-row spacing might be due to less available nitrogen for the plant growth
which lead to reduced vegetative growth and early flowering as described by Al-Fraihat
(2009). However, the decrease in bolting percentage in response to the application of 82 and
123 kg N ha-1) and wider spacing (10 and 12.5 cm) intra-row spacing may be associated with
enhanced availability of nitrogen and less stiff competition among plants for resources which
may have led to enhanced vegetative growth and delayed maturity thereby enhancing
vegetative growth that would slow bolting.

Similar observations were made by Al-Fraihat (2009) and Abdissa et al. (2011) where
increased nitrogen fertilizer applications reduced percentage of bolters in onions. Consistent
with the results of this study, Bosch and Olivé (1999) also reported that the increased
population density of onion significantly increased number of bolters. Mohamed (1991) also
indicated that closer spacing of 5 x 20 cm increased percentage of bolters by 14.5%, while
nitrogen application decreased the incidence of bolting.
 37

Table 5: Interaction effect of intra-row spacing and nitrogen fertilizer levels on dry total
biomass, days to maturity and bolting percentage of onion

Intra-row spacing Parameters

-
N level (kg ha (cm) Dry total Days to Bolting
1
) biomass maturity percentage
(g plant-1) (%)
0 2.5 2.72n 100.00i 31.95a
5 3.32lm 102.00hi 29.45a
7.5 3.62l 104.67gh 26.40b
10 4.82j 110.3cde 21.33cd
12.5 5.98i 105.00gh 11.36ij
41 2.5 3.23m 101.76hi 23.72c
5 4.84j 106.00g 21.74cd
7.5 6.24i 105.33gh 20.60d
10 7.09h 110.33ef 19.59de
12.5 8.75fg 115.0cd 8.68jk
82 2.5 4.02k 107.33fg 17.21ef
5 8.53g 113.00de 14.24gh
7.5 9.77e 115.67cd 11.88hi
10 11.54c 119.67b 6.37kl
12.5 12.59b 124.33a 4.17l
123 2.5 4.01k 113.33de 15.16fg
5 8.90f 115.67cd 12.41hi
7.5 10.38d 117.67bc 10.74ij
10 12.25b 123.33 a 4.98l
12.5 13.08a 126.67a 3.93l
CV (%) 2.85 1.86 9.93
SE (±) 0.12 1.20 0.91
Means followed by the same letter with in a column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests

4.2.9. Stand count percentage

The different intra-row spacing and nitrogen rates exerted a statistically significant (P < 0.01)
difference on stand count percentage of onion. Nevertheless, the interaction of effect intra-row
spacing and nitrogen fertilizer levels did not show significant variation on this parameter
(Appendix Table 1).
 38

In response to widening the intra-row spacing, stand count percentage increased significantly.
Hence, the highest stand count was obtained for 12.5 cm intra-row spacing. Generally, up on
increasing the intra-row spacing from 2.5 cm to 12.5 cm, the stand count percentage increased
from 78.56 to 98.04%. Thus, when the intra-row spacing increased to 12.5 cm, the stand count
percentage increased by 25% as compared to the narrowest intra-row spacing (Table 6).

The higher stand count percentage at higher intra-row spacing could be attributed to less
interplant competition for growth factors. Thus, the unavailability of the major plant food
nutrient as a result of which the plants became weaker and lower in number (Khan et al,
2002). The current result is in conformity with that of Ashenafi et al. (2014) who indicated
that higher population density led to lower stand count percentage of onion due to its higher
mortality rate. Khan et al. (2002) also found reduced plant competition and plant mortality in
onion at the lower plant population densities thereby resulted in increased stand count
percentage.

With the increase in the rate of nitrogen fertilizer application from nil to 82 kg N ha-1, stand
count percentage increased significantly. Thus, the highest stand count percentage was
obtained from nitrogen rate of 82 kg ha-1. In contrast, the nil nitrogen fertilizer rates produced
the lowest stand count percentages. In response to the increasing rate of nitrogen from 0 to 41
kg ha-1, stand count percentage increased by 1.4%. When increasing the rate of nitrogen from
41 to 82 kg ha-1, the stand count percentage further increased by about 0.3%. However,
increasing the rate of nitrogen beyond 82 kg N ha-1 did not change stand count percentage.
Increasing application of nitrogen from 0 to 82 kg N ha-1 increased stand count percentage by
about 2% (Table 6).

The increase in stand count percentage of onion at 82 kg N ha-1 might be associated with less
interplant competition among plants for growth factors. This report is consistent with the
finding of Ghaffoor et al. (2003) who showed that survival percentage of onion bulbs
increased when 150 kg N ha-1 was applied. Jilani et al. (2004) also reported that minimum
numbers of bulbs were recorded for the control level of nitrogen.
 39

Table 6: Main effect of intra-row spacing and nitrogen fertilizer levels on stand count
percentage of onion

Treatments Stand count (%)

Intra-row spacing (cm)
2.5 78.56e
5 86.42d
7.5 89.63c
10 97.30b
12.5 98.04a
Nitrogen levels ( kg ha-1)
0 88.83 c
41 90.06b
82 90.33ab
123 90.75a
SE(±) 0.48
CV (%) 0.93
Means followed by the same letter in a column are not significantly different at 5% probability
level according to Duncan’s Multiple Range Tests

4.3. Yield and Yield Related Traits

4.3.1. Average bulb weight

The main effect of nitrogen and that of intra-row spacing significantly (P <0.01) influenced the
average bulb weight of the onion plants. In addition, the two factors interacted to influence this
parameter significantly (P < 0.01) (Appendix Table 2).

Increasing the rate of nitrogen application progressively increased the average bulb weight of
the onion plants across the increasing intra-row spacing. Thus, the highest average bulb weight
was found in response to the application of 123 kg N ha-1 and intra-row spacing of 12.5 cm
due to the wider spacing accommodated less number of plants which received adequate
nutrient, moisture and light which helped to increase the average weight of bulb per plant
(Khan et al., 2002). However, the lowest average bulb weight was obtained at the lowest
nitrogen rate (0 kg ha-1) and smallest intra-row spacing (2.5 cm) (Table 7) due to absence of
external supply of nitrogen, which is an important element needed for proper growth and
development of every plant including onion (Brady, 1985).
 40

In harmony with this result, Muhammad et al. (2011), Mahadeen, (2008), Dorcas et al. (2012)
and Jilani et al. (2010) found that the lowest average bulb weight was obtained for narrowly
spaced onion plants. Corroborating the results of this study, Soleymani and Shahrajabian
(2012), Aliyu et al. (2008) and Morsy et al. (2012) mentioned that average bulb weight of
onion increased with nitrogen rate.

4.3.2. Bulb diameter

The main effect of nitrogen and that of intra-row plant spacing significantly (P < 0.01)
influenced the onion bulb diameter. The two factors interaction also influenced this parameter
significantly (P < 0.01) (Appendix Table 2).

Similar to the average bulb weight, increasing the rate of nitrogen application consistently
increased the bulb diameter of onion across the increasing intra-row spacing. Thus, the widest
bulb diameter was recorded in response to the application of 123 kg N ha-1 and intra-row
spacing of 12.5 cm. The narrowest average bulb diameter was obtained at the lower nitrogen
rates and smaller intra-row spacing of 2.5 and 5.0 cm (Table 7).

The development of wider bulb diameter with increasing intra-row spacing and rate of N
fertilizer could be associated with the availability of more growth resources due to less
competition and with application of N, which could be associated with promoting nature of
nitrogen in cell elongation, above ground vegetative growth and synthesis of chlorophyll to
impart dark green color of leaves. This may be linked to metabolic processes which increase
dry matter production and translocation to the bulbs (Brady, 1985).

The current results are supported by the findings of Jilani et al. (2009), Akoun (2005) and
Muhammad et al. (2011) who stated that higher bulb diameter was achieved for the wider
plant spacing as compared to the closer spacing of onion. Similarly, Soleymani and
Shahrajabian (2012) showed that nitrogen fertilization increased bulb diameter of onion
compared to the control plots. Ghaffoor et al. (2003) also reported that the nitrogen dose of
120 kg N ha–1 proved the best for the maximum bulb diameter of onion.
 41

4.3.3. Bulb neck diameter

The main effect of nitrogen and that of intra-row spacing significantly (P < 0.01) affected the
bulb neck diameter. The interaction effect of the two factors also influenced bulb neck
diameter of onion (P < 0.01) (Appendix Table 2).

Just like the average bulb weight and bulb diameter, increasing the rate of nitrogen application
consistently increased bulb neck diameter across the increasing intra-row spacing. Thus, the
widest bulb neck diameter was recorded in response to the application of 82 and 123 kg N ha -1
and intra-row spacing of 12.5 cm. The narrowest bulb neck diameter, on the other hand, was
obtained in combination to the application of nil rate of nitrogen fertilizer and intra-row
spacing of 2.5, 5.0, and 7.5 cm (Table 7).

The highest bulb neck diameter at the wider intra-row spacing and higher nitrogen dose may
be attributed to vigorous growth of the plants as a result of less stiff competition for growth
resources. On the other hand, the narrow intra-row spacing with its high plant populations may
have exerted pressure on scarce growth resources such as light, space, moisture and nutrients,
leading to reduced growth and narrow bulb neck diameter (Khan et al., 2002). Analogous
findings were mentioned by Dawar et al. (2005), Jilani et al. (2009) and Kantona et al. (2003)
who showed that bulb neck diameter of onion decreased in response to increasing onion
population density. Consistent with the results of this study, Jilani et al. (2004) reported that
application of N at the rate of 200 kg ha-1 increased the number of thick-necked bulbs.

4.3.4. Bulb dry matter yield

The analysis of variance revealed that bulb dry matter yield per plant of onion was
significantly (P < 0.01) affected by the main effect of the intra-row spacing and nitrogen
fertilizer rate. Moreover, the interaction effect of these two factors also revealed significantly
(P < 0.01) influence on bulb dry matter yield (Appendix Table 4).
 42

Increasing the rate of nitrogen application steadily increased the bulb dry matter yield of the
onion plants across the increasing intra-row spacing. Accordingly, the highest bulb dry matter
was found in response to the application of 123 kg N ha-1 and 82 kg N ha-1 and spaced at the
intra-row spacing of 12.5 cm. On the other hand, lower bulb dry matter yield was achieved at
the nil nitrogen rates and narrowest intra-row spacing. Thus, when plants were grown at the
lower treatment combinations of 0 kg N ha-1 and 2.5 cm of intra-row spacing, the bulb dry
matter yield of onion decreased by about 80% as compared to the higher rate of nitrogen (123
kg ha-1) and the widest intra-row spacing (12.5 cm) (Table 7).

The lower bulb dry matter yield of onion observed at closer intra-row spacing and application
of the nil rate of nitrogen might be due stiffer to competition among plants for the limited
growth resources, which may have resulted in reduced vegetative growth like leaf number, leaf
diameter, leaf length and plant height (Khan et al., 2002). Thus, finally the weight of bulb and
diameter becomes small, leading to lower value of bulb dry matter of onion. These results are
in conformity with the findings of Dereje et al. (2012) and Sikder et al. (2010) who explained
that higher bulb dry weight was achieved in wider spacing in shallot and onion respectively.
This result is consistent with the findings of Yadav et al. (2003) and El-Tantawy and El-Beik
(2009) who found that higher N doses resulted in the production of higher bulb dry matter
yields than lower doses of nitrogen.
 43

Table 7: Interaction effect of intra-row spacing and nitrogen fertilizer levels on average bulb
weight, bulb diameter, neck diameter and bulb dry matter yield per plant of onion

Intra-row Parameters
N level (kg spacing Average bulb Bulb diameter Neck Bulb dry
ha-1) (cm) weight (cm) diameter matter
(g) (cm) (g plant-1)
0 2.5 23.99l 2.33l 0.68k 2.00m
5 27.09kl 2.62k 0.69jk 2.45l
7.5 31.20jk 3.50i 0.74jk 2.70l
10 34.21ij 3.63hi 0.84gh 3.56j
12.5 41.88gh 3.90g 0.84gh 4.42i
41 2.5 38.48hi 3.07j 0.75ij 2.42l
5 46.77g 3.52i 0.81hi 3.59j
7.5 55.41f 3.70hi 0.89fg 4.68i
10 66.83e 4.80e 0.96de 5.39h
12.5 70.18e 5.23d 1.00d 6.55g
82 2.5 53.62f 3.50i 0.87fgh 3.05k
5 71.11e 4.46f 0.97de 6.82fg
7.5 77.23d 4.70e 1.07c 7.70e
10 90.79c 5.27d 1.11c 8.83c
12.5 101.64b 5.48c 1.38a 9.63a
123 2.5 59.89f 3.80gh 0.92ef 3.04k
5 78.03d 4.88e 1.12c 7.03f
7.5 85.15c 5.57c 1.21b 8.10d
10 99.02b 5.77b 1.25b 9.30b
12.5 123.85a 6.05a 1.35a 9.86a
CV 5.66 2.60 3.97 3.00
SE(±) 2.08 0.06 0.02 0.01
Means followed by the same letter with in a column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests

4.3.5. Total bulb yield

The main effect of nitrogen as well as that of intra-row spacing significantly (P < 0.01)
influenced the total bulb yield of onion. Additionally, the interaction effect of nitrogen
application and intra-row spacing significantly (P < 0.01) influenced the total bulb yield of the
onion (Appendix Table 2).
 44

Total bulb yield increased significantly in response to increasing the rate of nitrogen
application across the increasing rate of the intra-row spacing except in treatment combination
of nil nitrogen application of which it deceased with increasing intra-row spacing. However,
the increase occurred only up to the application of 82 kg N ha -1 and 5.0 cm intra-row spacing,
beyond which the total bulb yield decreased. The highest total bulb yield was obtained from
onion plants grown at the rate of 82 kg N ha-1 and the intra-row spacing of 5.0 cm. On the
other hand, the lowest total bulb yield was obtained in response to no application of nitrogen at
the rate of nil kg N ha-1 and intra-row spacing of 10.0 cm and 12.5 cm. Thus, the total bulb
yield obtained in response to the application of 82 kg N ha-1 at the intra-row spacing of 5.0 cm
exceeded the total bulb yield obtained from plants grown with no application of the N fertilizer
at the intra-row spacing of 2.5 cm by 90% (Table 8).

The enhancement of total bulb yield in response to the treatment combination of 5 cm intra-
row spacing and 82 kg N ha-1 might be due to the higher number of harvestable bulbs per unit
area as described by Latif et al. (2010). Hence, onion plants planted at the optimum intra row
spacing helps for attaining their optimum bulb size (Rumpel et al., 2000). However, bulb yield
per plant was observed to have increased with increase in intra row spacing at all nitrogen
rates via increasing their bulb weight. This result agrees with the finding of Khan et al. (2003),
Muhammad et al. (2011), Latif et al. (2010), Yemane et al. (2013) and Jan et al. (2003) who
reported that the highest onion bulb yields were observed at the closest spacing. Dereje et al.
(2012) also indicated that total bulb yield decreased with increase in the intra-row spacing of
shallot.

Similarly, Jilani et al. (2004) showed that with increase in dose of nitrogen up to120 kg ha–1,
the total bulb yield was increased, but below this rate, the total bulb yield began to decrease.
Soleymani and Shahrajabian, (2012) and Al-Frahat (2009) also indicated that the control plots
achieved lower total yields as compared to the higher nitrogen doses. Balemi et al. (2007) also
observed a significant increase in total bulb yield in response to increased application of
nitrogen.
 45

4.3.6. Unmarketable bulb yield

Unmarketable bulb yield was significantly influenced by the combined effect of intra-row
spacing and nitrogen fertilizer levels. Moreover, significant (P < 0.01) variations were
observed in this parameter in response to the main effects of both intra-row spacing and
nitrogen fertilizer rate (Appendix Table 2).

With the increase in the intra-row spacing and nitrogen fertilizer rate, unmarketable bulb yield
of onion decreased significantly. Thus, the highest value of unmarketable bulb yield was
recorded in zero nitrogen fertilizer application at the intra-row spacing of 2.5 cm. This was
followed by the narrow intra-row spacing at the rate of 41 kg N ha-1. On the other hand, the
minimum unmarketable bulb yield was obtained both when onion plants were fertilized with
123 kg N ha-1 and planted at spacing of 5.0 cm, 7.5 cm, 10 cm and 12.5 cm of intra-row
spacing and when the 82 kg N ha-1 was combined with the intra-row spacing of 7.5 cm, 10 cm
and 12.5 cm. Similarly, when 12.5 cm of intra-row spacing was combined with 41 kg N ha-1,
minimum unmarketable bulb yield was produced.

The higher unmarketable bulb yield of closely spaced onion plants and combined with nil
nitrogen levels (2.5 cm and 0 kg N ha-1) might be due to more interplant competition for
nutrient, water, light and air (Sikder et al, 2010). These results are in accord with those of
Seck and Baldeh (2009), Yemane et al. (2013) and Dereje et al. (2012) who mentioned that
narrow intra-row spacing increased unmarketable bulb yield of onion, onion, and shallot
respectively. Similarly, Brewster (1994) reported that under sub-optimal supply of nitrogen,
the marketable yields of onion and shallot can be severely reduced. Likewise, Negash et al.
(2009) and Jilani et al. (2004) indicated that nil nitrogen fertilizer rates resulted in more
unmarketable bulb yield.

4.3.7. Marketable bulb yield

The main effect of nitrogen as well as that of intra-row spacing significantly (P < 0.01)
influenced the marketable bulb yield of the onion crop. Similarly, the interaction effect of
 46

nitrogen application and intra-row spacing significantly (P < 0.01) influenced the marketable
bulb yield of the crop (Appendix Table 2).

Similar to the total bulb yield, increasing the rate of nitrogen application significantly
increased the production of marketable bulb yield across the increasing rate of the intra-row
spacing. However, the increase occurred only up to the application of 82 kg N ha-1 and 5.0 cm
intra-row spacing, beyond which the marketable bulb yield decreased. Thus, the highest
marketable bulb yield was recorded from onion plants grow at the rate of 82 kg N ha -1 and the
intra-row spacing of 5.0 cm. On the other hand, the lowest marketable bulb yield was obtained
in response to no application of nitrogen combined with the intra-row spacing of 2.5 cm. Thus,
the marketable bulb yield obtained in response to the application of 82 kg N ha-1 at the intra-
row spacing of 5.0 cm exceeded the marketable bulb yield of plants grown with no application
of the N fertilizer at the intra-row spacing of 2.5 cm by 120% (Table 8).

The maximum marketable bulb yield of onion obtained at treatment combination of 5 cm

intra-row spacing and 82 kg N ha-1 might be attributed to optimum number of plant population
per unit area which leads to maximum number of bulbs due to closer spacing and optimal
supply of nitrogen in the soil. Although plant height, number of leaves per plant and leaf
length increased with increasing spacing, it could not be compensated for the yield of closely
spaced plants due to higher plant population. Thus, the marketable bulb yield of onion per unit
area does not completely depend up on the performance of individual plants but also related
with the total number of plants per unit area and yield contributing parameters (Latif et al.,
2010 and Aliyu et al., 2008).

Similar observations were reported by Latif et al. (2010), Jan et al. (2003), Sikder et al.
(2010), Dorcas et al. (2012) and Mahadeen (2008) who reported that maximum marketable
bulb yields of onion were obtained at lower intra-row spacing. Islam et al. (1999) and Naik
and Hosamani (2003) also stated that maximum bulb yield of onion was recorded in treatment
combination of narrow intra-row spacing and optimum nitrogen fertilizer level. Similarly,
Soleymani and Shahrajabian (2012) and Balemi et al. (2007) also showed that the higher value
of marketable yield was achieved under higher rate of nitrogen fertilization (120 kg ha-1).
 47

Table 8: Interaction effect of intra-row spacing and nitrogen fertilizer levels on marketable,
unmarketable and total bulb yield of onion

Intra-row Parameters
N level (kg spacing (cm) Marketable bulb Unmarketable bulb Total bulb yield
ha-1) -1
yield (t ha ) -1
yield (t ha ) (t ha-1)
0 2.5 17.93j 2.96 a 20.89i
5 19.41i 1.32c 20.73ij
7.5 19.39i 0.97e 20.36ij
10 18.75ij 0.88ef 19.63jk
12.5 18.13j 0.76g 18.89k
41 2.5 21.36h 1.87b 23.23h
5 27.63e 0.85fg 28.48e
7.5 26.98e 0.41h 27.39ef
10 22.97g 0.19i 23.17h
12.5 23.21g 0.15ijk 23.36h
82 2.5 24.13fg 1.14d 25.27g
5 39.51a 0.19ij 39.69a
7.5 36.17b 0.14ijk 36.31b
10 31.00d 0.13ijk 31.13d
12.5 24.76f 0.08jk 24.84g
123 2.5 23.23g 0.47h 23.70h
5 37.02b 0.14ijk 37.16b
7.5 33.65c 0.07jk 33.73c
10 26.47e 0.04k 26.51f
12.5 23.18g 0.03k 23.21h
CV (%) 2.61 10.00 2.55
SE (±) 0.39 0.04 0.39
Means followed by the same letter are with in a column not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests

4.3.7.1. Bulb size distribution of marketable bulb yield

4.3.7.1.1. Small-sized bulb yield (20-50g)

The analysis of variance showed that both the main effect of intra-row spacing and nitrogen
fertilizer level and their interaction effect significantly (P < 0.01) influenced the small bulb
size distribution of onion (Appendix Table 3).
 48

Increasing the intra-row spacing significantly decreased the production of small sized bulb
yield across the increasing rate of nitrogen application rate. Thus, the highest small sized bulb
yield was obtained from onion plants grown at the rate of 0 kg N ha-1 and 41 kg N ha-1 and
spaced at the intra-row spacing of 2.5 cm. In contrast, the lowest small sized bulb yield of
onion was recorded in response to the application of higher nitrogen rate at 123 kg ha-1 and 82
kg ha-1 and planted at the intra-row spacing of 10 cm and 12.5 cm. For instance, the small
sized bulb yield obtained in response to the application of 0 kg N ha-1 planted at the intra-row
spacing of 2.5 cm exceeded small sized bulb yield of plants grown with 123 kg ha-1
application of the N rates planted at the intra-row spacing of 12.5 cm by 2131% (Table 9).

The increment in small size bulb yield of onion in response to the application of nil nitrogen
rate and narrow intra-row spacing may have resulted in reduction in above growth biomasses
like leaf number, leaf area, leaf length and diameter due to less availability and more
competition for growth resources. With narrower plant spacing, bulb expansion suffers
(Rumpel et al., 2000; Negash et al., 2009). In accordance with the current finding, increasing
the rate of nitrogen application from 0 kg ha-1 to 138 kg ha-1 significantly decreased the yield
of small sized bulbs of onion by 61.8% as reported by Negash et al. (2009). Similarly, Nasreen
et al. (2007) indicated that small size bulb yield reduction in response to increased N
fertilization. Moreover, supporting the current result, Dorca et al. (2012), Balraj et al. (1998)
and Yemane et al. (2013) indicated that higher population density increased the yield of small-
sized bulbs.

4.3.7.1.2. Medium bulb size yield (50-100g)

Intra-row spacing and nitrogen fertilizer levels exhibited highly significant (P < 0.01) variation
on medium bulb size yield of onion. Likewise, interaction effect also exerted a significant (P <
0.01) influence on this parameter (Appendix Table 3).

The production of medium sized bulb yield of onion was significantly increased by increasing
the nitrogen rate application across the increasing of intra-row spacing. However, the increase
was not consistent and occurred only up to the nitrogen rate of 82 kg N ha-1 at the intra-row
 49

spacing of 5.0 cm, beyond which the medium sized bulb yield decreased. However, medium
sized bulb yield increased with application of nil nitrogen rates spaced at all intra-row spacing.
Hence, the highest medium sized bulb yield was achieved from onion plants grown with the
application of 82 kg N ha-1 at the intra-row spacing of 5.0 cm. On the other hand, in response
to nil application of nitrogen and planted at the intra-row spacing of 2.5 cm produced the
lowest medium sized bulb yield. Thus, the medium sized bulb yield obtained in response to the
application of 82 kg N ha-1 at the intra-row spacing of 5.0 cm exceeded the medium sized bulb
yield of plants grown with the application of 0 kg N ha-1 at the intra-row spacing of 2.5 cm by
632% (Table 9).

The increase in medium sized bulb yield of onion in response to the application of 82 kg ha-1
nitrogen at the intra-row spacing of 5.0 cm may be due to the fact that this rate of nitrogen and
intra-row spacing were optimum for growth and enhanced productivity of the crop. The results
of the present study are in agreement with the finding of Negash et al. (2009) and Nasreen et
al. (2007) who reported that highest weights of medium sized bulb yield were recorded at
application of higher nitrogen. Similarly, Nasir et al. (2007), Rumpel et al. (2000) and Stoffela
(1996) reported that maximum weights of medium sized bulbs were obtained at higher
planting densities.

4.3.7.1.3. Large-sized bulb yield (100-160g)

The analysis of variance showed that the main effect of nitrogen rate was significant (P < 0.01)
on large sized bulb yield of onion. The main effect of intra-row spacing also significantly (P <
0.01) affected large sized bulb yield. Moreover, nitrogen and intra-row spacing interacted to
influence this parameter (Appendix Table 3).

Similar to medium sized bulb yield, large sized bulb yield increased significantly in response
to the increased application of nitrogen rate across the increasing of intra-row spacing except
for the application of nitrogen rate of nil and 41 kg ha-1 combined with all the intra-row
spacing. However, the increase occurred only up to the nitrogen application and intra-row
spacing combination of 82 kg N ha-1 and 7.5 cm of intra-row spacing above which decrease in
 50

the yield of large sized bulb occurred. When the onion plants were spaced at 2.5 cm large
sized bulb yield increased across the different nitrogen rates. The maximum large sized bulb
yield was obtained in response to the application of 82 kg N ha-1 and intra-row spacing of 7.5
cm. On the other hand, the minimum value was achieved from the treatment combination of
narrowest intra-row spacing and nil nitrogen rate (Table 9).

The achievements of higher yields of large sized bulbs by increasing intra-row spacing up to
the optimum intra-row spacing and N level might be due to resource availability and
assimilation and less stiff competition among the onion plants (Khan et al., 2002). This may
lead to increased weights of individual bulbs shifting from small to medium and then to large
bulb categories. Corroborating this result, Negash et al. (2009) and Kokobe et al. (2013)
reported that onion bulb size increased with increasing nitrogen dose. Islam et al. (1999) also
explained that large sized bulbs were recorded for wider intra-row spacing and higher nitrogen
rates. Similarly, Dawar et al. (2007), Jilani et al. (2009), Yemane et al. (2013) and Mallor et
al. (2011) indicated that maximum value of large bulbs were obtained in lower population
densities.

4.3.7.1.4. Over-sized bulb yield (>160 g)

The main effect of intra-row spacing and nitrogen fertilizer rates significantly (P < 0.01)
affected oversized bulb yield of onion. Interaction effect of intra-row spacing and nitrogen rate
also exerted a significant (P < 0.01) influence on oversized bulb yield of onion (Appendix
Table 3).

Increasing the rate of nitrogen markedly increased over sized bulb yield of onion across the
increasing intra-row spacing. Thus, the lowest oversized bulb yield was recorded when the
onion plants were grown with nil nitrogen fertilizer application and planted at the intra-row
spacing of 2.5 cm, 5.0 cm, 7.5 cm and 10 cm as well as when the onion plants were treated
with 41 kg N ha-1 and 2.5 cm intra-row spacing. Nevertheless, intra-row spacing and nitrogen
rate combinations of 123 kg ha-1 and 12.5 cm intra-row spacing resulted in the highest over-
sized bulb yield of onion.
 51

The lower oversized bulb yield recorded at narrow intra-row spacing and nil rate of nitrogen
application might be due to stiffer competition among onion plants for growth resource, which
may have resulted in smaller bulb expansion in size (Rumpel et al., 2000). On the other hand,
ample availability of growth resources including wider space may lead to high bulb expansion
and growth, leading to the production of markedly higher yields of over-sized bulbs.
Comparable results were reported by Khan et al. (2002), Coleo et al. (1996) and Nasir et al.
(2007) that the highest proportions of large bulbs were found at lower planting densities.
 52

Table 9: Interaction effect of intra-row spacing and nitrogen fertilizer levels on marketable
bulb size distribution of onion

Intra-row Parameters
N level (kg spacing Small sized Medium sized Large sized Oversized bulb
ha-1) (cm) bulb yield bulb yield bulb yield yield
-1 -1 -1
(t ha ) (t ha ) (t ha ) (t ha-1)
0 2.5 13.83a 3.86m 0.25j 0.00j
5 10.07b 8.49k 0.85hi 0.00j
7.5 7.95c 10.52j 0.91hi 0.05j
10 6.37d 11.19ij 1.19gh 0.11ij
12.5 4.79e 11.71i 1.63g 0.22ghi
41 2.5 13.17a 7.50l 0.69ij 0.09ij
5 9.30b 16.67ef 1.66g 0.22hi
7.5 7.88c 16.95de 2.15f 0.31gh
10 4.54ef 15.82fg 2.61e 0.36g
12.5 3.50g 13.35h 6.36d 0.73e
82 2.5 9.56b 13.51h 1.05hi 0.22ghi
5 3.72fg 28.27a 7.59bc 0.72e
7.5 3.26g 24.89b 8.03a 1.02d
10 1.51h 22.08c 7.41bc 1.44c
12.5 0.67h 16.84e 7.25bc 2.39b
123 2.5 7.55c 14.03h 1.64g 0.56f
5 3.81fg 25.64b 7.58b 0.97d
7.5 3.70fg 22.62c 7.34bc 1.31c
10 1.33h 17.85d 7.29bc 2.47b
12.5 0.62h 15.49g 7.04c 4.03a
CV (%) 8.63 3.59 6.69 9.61
SE(±) 0.29 0.33 0.16 0.05
Means followed by the same letter with in a column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests

4.3.8. Under size bulb yield (< 20 g)

Results from the analysis of variance revealed that combined effect of intra-row spacing and
nitrogen fertilizer rate was found to be significant (P < 0.01) on under sized bulb yield. Effect
of the different intra-row spacing and nitrogen level also significantly (P < 0.01) affected the
under sized bulb yield of onion (Appendix Table 3).
 53

Across with widening intra-row spacing, increasing the rate of nitrogen application markedly
decreased the yield of under sized bulbs. Therefore, the maximum under sized bulb yield was
recorded when onion plants were fertilized with 0 kg N ha-1 at the spacing of 2.5 cm intra-row
spacing. Next to this treatment combination, a high value of under sized bulb yield was
recorded at treatment combination of 2.5 cm intra-row spacing and 41 kg N ha-1. Conversely,
the minimum under-sized bulb yield was recorded at the treatment interaction of 123 kg N ha-1
and 7.5 cm, 10 cm and 12.5 cm intra-row spacing. In line with this, onion plants treated with
82 kg N ha-1 and 12.5 cm intra-row spacing produced a minimum under-sized bulb yield of
onion (Table 10).

The higher under sized bulb yield at closer intra-row spacing combined with nil nitrogen level
could be due to more competitive effect among the different planting density for growth
resources at the closer plant spacing. The increase in the yield of the under-sized bulbs might
also be related with the lower nitrogen doses, which may have reduced vegetative growth like
leaf number, leaf area and leaf length by decreasing synthesis and partitioning of
photosynthetic to the bulbs (Rumpel et al., 2000). In harmony with this result, higher under-
sized bulb yield of onion at the highest planting density was reported by Nasir et al. (2007).
Similarly, Jilani et al. (2009) showed that minimum bulb sized yield obtained in the control
plots or nil nitrogen dose. Negash et al. (2009) reported that nil nitrogen fertilizer application
increased small sized bulbs yield of onion.

4.4. Harvest Index

The analysis of variance showed that means of harvest index was significantly (P < 0.01)
affected by the interaction effect of nitrogen and intra-row spacing. Moreover, harvest index
was significantly (P < 0.01 influenced by the main effects of nitrogen application and intra-
row spacing) (Appendix Table 4).

In response to increasing the rate of nitrogen application across the increasing rate of the intra-
row spacing, harvest index increased markedly. Thus, the highest harvest index was recorded
from the application of nitrogen at the rate of 82 kg ha-1 and intra-row spacing of 5.0 cm and
7.5 cm. Application of 123 kg N ha-1 at the intra-row spacing of 5.0 cm also produced the
 54

maximum harvest index. On the other hand, onion plants that received 0 kg N ha-1 and at the
intra-row spacing of 2.5 cm, 5.0 cm, 7.5 cm, 10 cm and 12.5 cm had the minimum harvest
indices. Similarly, application of 41 kg N ha-1 combined with all the intra-row spacing, except
10 cm, led to the lowest in harvest index. For instance, the harvest index of onion plants
treated with nil nitrogen at the intra-row spacing of 2.5 cm decreased by about 8% compared
to the harvest index obtained in response to the application of 82 kg N ha-1 at the intra-row
spacing of 5 cm.

The highest harvest index at the optimum intra-row spacing and optimum nitrogen fertilizer
levels (5 cm with 82 kg N ha-1) could be associated with comparatively high marketable bulb
yield. It might also be related with the presence of relatively shorter leaf length and leaf
diameter and plant height in treatment combination of 5 cm with 82 kg N ha-1, which may
have reduced the above ground biomass and resulted in higher harvest index (Kabir and Sarkar
2008; Yemane et al., 2013). On the other hand, the lowest harvest index in the treatment
combination of 0 kg N ha-1 and 2.5 cm intra-row spacing may be due to relatively lower
marketable bulb yield. Similar results were obtained by Abdissa et al. (2011) who reported
that the lowest harvest index of onion occurred in response to the application of nil rate of
nitrogen fertilizer. Similarly, Yemane et al. (2013) for onion and Dereje et al. (2012) for
shallot reported that wider intra-row spacing resulted in lower harvest indices. Highest values
of harvest index of mungbean was recorded from closer spacing probably due to the reduced
vegetative biomass (Kabir and Sarkar, 2008).

4.5. Total Soluble Solid

The main effect of nitrogen as well as that of intra-row spacing significantly (P < 0.01)
influenced the total soluble solids of the onion plants. Moreover, nitrogen application and
intra-row spacing interacted to significantly (P < 0.01) influence the total soluble solids of the
crop (Appendix Table 4).

Increasing rate of nitrogen application significantly increased total soluble solids, but the
parameter consistently decreased across the increasing intra-row spacing. Thus the highest
total soluble solids were recorded for plants grown at the rates of 82 and 123 kg N ha -1 and at
 55

the intra-row spacing of 2.5 cm. On the other hand, the smallest total soluble solids were
recorded for onion plants grown at the nil rate of nitrogen application and planted at the intra-
row spacing of 10 cm and 12.5 cm. Thus, the total soluble solids recorded at the rates of 82
and 123 kg N ha-1 and the intra-row spacing of 2.5 cm exceeded the total soluble solids
obtained at nil rate of N fertilizer and the intra-row spacing of 10 and 12.5 cm by about 32 and
35%, respectively.

The possible reason for increasing the total soluble solids with higher application of nitrogen
fertilizer along with narrow intra-row spacing might be higher nitrogen content increases the
chlorophyll content and dry weight per plant (Brady, 1985). The wider intra-row spacing also
resulted in larger onion bulbs which gets its soluble solids diluted due to higher volume and
more water content (Mallor et al., 2011). The results are in conformity with the findings of
Moursy et al. (2007) and Morsy et al. (2012) who stated that the application of nitrogen
fertilizer levels increased TSS values. Consistent with the results of this study, Naik and
Hosamani (2003) also showed that maximum TSS was recorded for higher nitrogen rates and
narrow intra-row spacing. Mallor et al. (2011) also reported a significant negative correlation
between bulb weight and soluble solids content.
 56

Table 10: Interaction effect of intra-row spacing and nitrogen fertilizer levels on under sized
bulb yield, harvest index and total soluble solid yield of onion

Parameters
N level Intra-row spacing Under sized bulb Harvest Total soluble
(kg ha- (cm) yield index solids
1 -1
) (t ha ) (%) (0Brix)
0 2.5 2.61a 73.25i 12.17ef
5.0 0.94c 74.00ghi 11.70hi
7.5 0.65e 74.61e-i 10.47l
10 0.46f 73.84hi 10.17m
12.5 0.45f 73.90hi 10.07m
41 2.5 1.70b 74.99d-i 12.57d
5 0.40fg 74.35f-i 12.10ef
7.5 0.36g 74.89d-i 11.73gh
10 0.17h 75.99def 10.63kl
12.5 0.13hi 74.84d-i 10.57l
82 2.5 0.79d 75.87def 13.33ab
5 0.17h 79.96a 12.90c
7.5 0.12hij 78.84ab 12.00fg
10 0.12hij 76.56cd 10.97j
12.5 0.05ijk 76.46cde 10.90jk
123 2.5 0.35g 75.83d-g 13.57a
5 0.12hij 78.94ab 13.20b
7.5 0.06ijk 78.02bc 12.33de
10 0.04jk 75.87def 11.43i
12.5 0.02k 75.39d-h 11.00j
CV (%) 10.35 1.27 1.43
SE (±) 0.03 0.55 0.10
Means followed by the same letter with in a column are not significantly different at 5%
probability level according to Duncan’s Multiple Range Tests

4.6. Correlation Analysis

Correlation coefficient was calculated for the different response variables which help to show
how the yield components and growth characters affecting the marketable bulb yield of onion.
Thus, it was observed that marketable bulb yield was highly significantly and positively
correlated with medium bulb size (r=0.95**), large bulb size (r=0.74**), total yield
(r=0.99**), leaf number (r=0.53**), plant height (r=0.56**), leaf length (r=0.47**), leaf
 57

diameter (r=0.45**), bulb diameter (r=0.47**), neck diameter (r=0.46**), average bulb weight
(r=0.50**), days to maturity (r=0.43**), bulb dry matter (r=0.55**), shoot dry matter
(r=0.39**), harvest index (r=0.84**), dry total biomass (r=0.52**) and TSS (r=0.46** )
(Appendix 5). This shows that the use of different combination of intra-row spacing and
nitrogen fertilizer levels for increasing of vegetative growth, results to the indirect selection of
intra-row spacing and nitrogen level combinations for increasing onion yield. However,
marketable yield was highly statistically and negatively correlated to unmarketable bub yield
(r=-0.56**), under sized bulb (r=-0.50**) and bolting percentage (r=-0.43**). Hyder et al.
(2007) also showed that plant height has positive indirect effect on marketable bulb yield and
bulb sizes.

Similarly, average bulb weight was positively correlated and highly significant with plant
height (r=0.86**), leaf number (r=0.91**), leaf length (r=0.79**), leaf diameter (r=0.95**),
bulb diameter (r=0.94**), neck diameter (r=0.95**), bulb dry matter (r=0.94**), days to
maturity (r=0.92**), harvest index (r=0.50**), dry total biomass (r=0.94*), medium size bulb
(r=0. 63**), large bulb size (r=0.86**), marketable bulb yield (r=0.50**), total yield
(r=0.44*), oversized bulb (r=0.91**) and shoot dry matter (r=0.93**) indicating that N
fertilization and intra-row spacing increased bulb weight by improving these parameters.
Abdissa et al. (2011) indicated that bulb weight had positively strongly association with plant
height, leaf number, leaf length and days to maturity as affected by nitrogen and phosphorus
fertilization.

Negatively and significantly association was observed as bulb weight was correlated with
unmarketable yield (r=-0.76**) and small bulb size (r=-0.85**), under size bulb (r=-0.68**)
and bolting percentage (r=-0.88**); but negatively and not significantly correlated with TSS
(r=-0.02ns) signifying that N level and intra-row spacing increasing bulb weight by decreasing
TSS contents. Mallor et al. (2011) also reported significant negative correlation found between
bulb weight and soluble solids content. Rajcumar (1997) also reported that high bulb weight
have lower total soluble solids content and a negative correlation (r=-0.85) between bulb size
and TSS.
 58

It was also observed that leaf number was positively correlated with total yield (r=0.47**),
plant height (r=0.84**), leaf length (r=0.75**), leaf diameter (r=0.94**), bulb diameter
(r=0.91**), and neck diameter (r=0.89**); plant height, leaf length, leaf diameter and shoot
dry matter was significantly and positively correlated with total yield (r=0.50**), (r=0.40**),
(r=0.37**) and (r=0.32**), respectively. This association indicates that an increased
photosynthetic area in response to N fertilization and intra-row spacing had noticeably
contributed to enhance onion yield and quality which could be through the production of more
assimilates and finally translocate to the bulbs (Marschner, 1995). Bulb diameter has also
strong and positive correlation (r=0.40**) with the total yield. Similar findings were also
reported by Nasreen et al. (2007).

4.7. Partial Budget Analysis

Partial budget is a method of organizing experimental data and information about the costs and
benefits of various alternative treatments. It is the process of examining only those costs,
returns and resource needs that change with a proposed adjustment. A partial budget is a way
of calculating the total costs that vary and the net benefits of each treatment (CIMMYT, 1988).

From the result of this study, the average yield of 20 treatments was obtained. According to
CIMMYT (1988), the average yield was adjusted down wards by 10 %. This is for the reason
that, researchers have assumed that using the same treatments the yields from the experimental
plots and farmers’ fields are different, thus average yields should be adjusted downward.
Based on this, the recommended level of 10% was adjusted from all 20 treatments to get the
net yield. In addition to this, to obtain the gross field benefits, it is essential to know the field
price value of one kg of onion bulb during harvesting time. Then finally, adjusted yield was
multiplied by field price to obtain gross field benefit of onion.

For the different treatment combinations the total costs and net benefits were calculated. The
different costs of this experiment which includes cost for nitrogen (Urea), seed and labour cost
for nitrogen fertilizer application and for transplanting are varied among the different
treatments. The purchasing price of Urea and seeds were 12.00 Birr kg-1 and 160.00 Birr kg-1
 59

respectively. The cost for daily labor during the season was 60 Birr per day. The field price of
onion during the harvesting season was 5 birr kg-1. All the variable costs were subtracted from
gross benefit to obtain net benefit.

The partial budget analysis revealed, the highest net benefit of Birr 168550 with higher cost
was recorded from the combination of 82 kg N ha-1 and 5 cm intra-row spacing with marginal
rate of 696% which was followed by net benefit of Birr 155408 from the nitrogen rate of 82 kg
ha- 1 and spacing of 7.5 cm intra-row spacing with the marginal rate of 2365%. However, the
highest net benefit of Birr 133087 with least cost production of about Birr 6413 were obtained
from application of nitrogen rate 82 kg ha-1 and 10 cm of intra row spacing with MRR of
(14372%).This means that for every Birr 1.00 invested in 82 kg N ha-1 and 10 cm intra-row
spacing, growers can expect to recover the Birr 1.00 and obtain an additional 143.72 Birr.

The minimum acceptable marginal rate of return (MARR %) should be between 50% and
100% CIMMYT (1988). Thus, the current study indicated that marginal rate of return is higher
than 100% (Table 11). This showed that all the treatment combinations are economically
important as per the MRR is greater than 100%. Hence, the most economically attractive
combinations for small scale farmers with low cost of production and higher benefits were in
response to the application of 82 kg N ha-1 and 10 cm intra row spacing. However, for
resource full producers (investors), application of 82 kg N ha-1 spaced at 5.0 cm intra row-
spacing was also profitable with higher cost and highest net benefit is recommended as a
second option.
 60

Table 11. Partial budget and MRR analysis for fertilizer rate and intra row spacing trial on
marketable yield of onion

N (kg ha-1) Unadjusted Adjusted Gross Variable Net Benefit MRR

with intra- marketable marketable Benefit cost (Birr ha-1) (%)
row (cm ) yield yield (Birr ha-1) (Birr)
combination (t ha-1) (t ha-1)
0*12.5 18.13 16.32 81600 2260 79340 0

0*10 18.75 16.88 84375 2834 81541 386

0*7 .5 19.39 17.44 87210 3778 83432 200

41*12.5 23.21 20.89 104445 4770 99675 1637

82*12.5 24.76 22.28 111400 5839 105581 552

41*7.5 26.98 24.28 121400 6288 115122 2124

82*10 31.00 27.90 139,500 6413 133087 14372

82*7.5 36.17 32.55 162,765 7357 155408 2365

82*5 39.51 35.56 177,795 9245 168550 696

 61

5. SUMMARY AND CONCLUSION

Onion (Allium cepa L.) is one of the most important vegetable crops commercially grown in
the world. It is a high value and high income generating vegetable crops for most farmers in
Ethiopia which is widely produced in small scales and by commercial growers. Onion is
considerably important in the daily Ethiopian diet which the bulbs and the lower stem sections
are the most popular as seasonings or as vegetables in stews.

The enhancement of onion production and productivity can be related with different growth
factors. Thus, the use of appropriate agronomic management has an undoubted contribution to
increased crop yields. Although several constraints are associated with onion production;
improper agronomic practice used by farmers are among the major problems to onion
production and productivity improvement in the study area. Hence, intra-row spacing and
nitrogen fertilizer levels are among the key agronomic practices which affect yield and quality
of onion bulbs.

A field experiment was carried out at Axum Agricultural Research Center during the 2014/15
cropping season with the objectives of to assess the effect of intra-row spacing and nitrogen
fertilizer level on growth, yield and quality of onion and to identify the appropriate intra-row
spacing and nitrogen fertilizer rate that improves yield and quality of onion. A factorial
randomized complete block design with 4 x 5 combinations in which four levels of nitrogen
fertilizer (0, 41, 82 and 123 kg ha-1) which results in 0, 89, 178, 267 kg Urea ha-1, respectively
and with five levels of intra-row spacing (2.5, 5, 7.5 10 and 12.5 cm), which resulted in
1333333, 666667, 444444, 333333, 266667 plants ha-1, respectively) was used with three
replications.

The analysis of variance showed that leaf number per plant, leaf length, leaf diameter, shoot
dry matter per plant, dry total biomass yield, days to maturity, bolting percentage, average
bulb weight, bulb diameter, bulb neck diameter, bulb dry matter per plant, marketable bulb
yield, unmarketable bulb yield, total bulb yield, small-sized bulb, medium-sized bulb, large-
sized bulb, over-sized bulb, under-sized bulb yield, harvest index and total soluble solid were
 62

significantly influenced by the interaction effect of intra-row spacing and nitrogen fertilizer
rates. However, plant height and stand count percentage had significantly affected due to the
main effects of intra-row spacing and different rates of nitrogen fertilizer.

From this study, significantly taller plant height was obtained at the intra-row spacing of 7.5
cm and 82 kg ha-1 nitrogen fertilizer rate. Likewise, higher leaf number per plant, leaf
diameter, shoot dry matter per plant, and dry total biomass were recorded in the treatment
combination of 12.5 cm intra-row spacing and 123 kg ha-1 nitrogen rate. Significantly,
maximum value of leaf length was produced in onion plants treated with nitrogen at the rates
of 82 and 123 kg ha-1 and spaced at 5.0, 7.5, 10.0, and 12.5 cm of intra-row spacing. However,
significantly, higher bolting percentage was recorded for plants grown at nil rates of nitrogen
fertilizer and intra-row spacing of 2.5 and 5.0 cm. Plants grown at the higher rates of nitrogen
application (123 kg and 82 kg ha-1) and the wider intra-row spacing (12.5 cm) were required
higher number of days to mature the onion plants. Moreover, the stand count percentage was
significantly increased with increasing intra-row spacing from 2.5 cm to 12.5 cm and nitrogen
fertilizer rates from 0 kg ha-1 up to 82 kg ha-1.

The highest average bulb weight and bulb diameter were produced at treatment combinations
of the widest intra-row spacing and the highest rate of nitrogen. Bulb neck diameter and bulb
dry matter per plant was higher at plants treated with both nitrogen rate of 82 kg ha-1 and 123
kg ha-1 and planted at the intra-row spacing of 12.5 cm. Increasing nitrogen rate of application
across the increasing intra-row spacing marketable bulb yield and total bulb yield were
markedly increased up to the nitrogen rate of 82 kg ha-1 and 5.0 cm intra-row spacing beyond
which it declines. Thus, the highest marketable bulb yield and total bulb yield were produced
at treatment combinations of 5.0 cm intra-row spacing along with nitrogen fertilizer
application of 82 kg ha-1. Likewise, the highest medium-sized bulb, and large-sized bulb yield
were obtained at 82 kg N ha-1 application when onion plants were spaced at 5.0 cm and 7.5 cm
intra-row spacing, respectively. However, significantly the highest value of unmarketable bulb
yield was produced in response to the application of nil nitrogen rate and 2.5 cm of intra-row
spacing.
 63

Response to increasing nitrogen rate across increasing intra-row spacing significantly

decreased the yield of small-sized bulb yield, and under-sized bulb yield. The highest yields of
these parameters were achieved in treatment combination of the narrowest intra-row spacing
and nil nitrogen application. However, increasing in nitrogen rate across increasing intra-row
spacing significantly increased in oversized bulb yield. Hence, the highest oversized bulb yield
was recorded in 123 kg N ha-1 application and 12.5 cm intra-row spacing. Onion plants that
received 123 kg N ha-1 at the intra-row spacing of 5.0 cm and nitrogen rate of 82 kg ha-1 intra-
row spacing of 5.0 cm and 7.5 cm had the maximum harvest indices. Total soluble solids were
achieved significantly higher in response to higher nitrogen dose of both 82 kg ha-1 and 123 kg
ha-1 and at the narrowest narrow intra-row spacing of 2.5 cm.

The partial budget analysis revealed, the highest net benefit of Birr 168550 with higher cost
(9245 Birr) was recorded from the combination of response to nitrogen rate of 82 kg ha-1 and 5
cm intra-row spacing with marginal rate of 696%. However, the highest net benefit of Birr
133087 with least cost of production about Birr 6413 were obtained from the treatment
interaction of 82 kg N ha-1 and 10 cm of intra row spacing with MRR of (14372%).

Therefore, the most economically attractive combinations for small scale farmers with low
cost of production and higher benefits were application of 82 kg N ha-1 and 10 cm of intra row
spacing in the study area. However, for growers who have full resources (investors),
application of 82 kg N ha-1 spaced at 5.0 cm intra row-spacing was also profitable with higher
cost of production and highest net benefit is recommended as a second option. However, as the
experiment was done for only one season and single location, it has to be repeated over
seasons and locations to make a conclusive recommendation.
 64

6. REFERENCES

Abdissa Yohanes, Tekalign Tsegaw and Pant, L.M. 2011. Growth, bulb yield and quality of
onion (Allium cepa L.) as influenced by nitrogen and phosphorus fertilization on
Vertisol I. Growth attribute biomass production and bulb yield. African Journal of
Agricultural Research. 6 (14):3252-3258.
Akoun, J. 2005. Effect of plant density and manure on the yield and yield components of the
common onion (Allium cepa L.) var. Nsukka red. Nigerian Journal of Horticultural.
Science, 9:43-48.
Al-Fraihat, A.H. 2009. Effect of different nitrogen and sulphur fertilizer levels on growth,
yield and quality of onion (Allium cepa L.). Jordan Journal of Agricultural Science,
5(2):155-166.
Aliyu, U. Dikko, A.U. Magaji, M.U. and Singh, A. 2008. Nitrogen and intra-row spacing
effects on growth and yield of onion (Allium cepa L.). Journal of Plant Science, 3(3):
188-193.
Ashenafi Woldeselassie, Helen Teshome and Tibebu Simon. 2014. Influence of bulb treatment
and spacing patterns on yield and quality of onion (Allium cepa var. Cepa) seed at
Humbo Larena, Southern Ethiopia. Journal of Biology Agriculture and Healthcare,
4(13):111-119.
AVRDC (Asian Vegetable Research Development Center). 2004. Asian Vegetable Research
and Development Center, Shanhua, Tainan, Taiwan. Vii 152p.
Bagali, A.N. Patil, H.B. Guled, M.B. and Patil, R.V. 2012. Effect of scheduling of drip
irrigation on growth, yield and water use efficiency of onion (Allium cepa L.). Journal
of Agricultural Science, 25 (1):116-119.
Balemi, T.P Netra and Anil, S.A. 2007. Response of onion (Allium cepa L.) to combined
application of biological and chemical nitrogenous fertilizers. Acta agriculture
Slovenica, 89(1):107-114.
Baloch, A.F. 1994. Vegetable crops. Horticulture. National Book Foundation, Islamabad,
Pakistan. pp. 489-537.
Balraj, S. Sharma, R.S. and Kumar, Y. 1998. Effect of bulb spacing and nitrogen levels on
growth and seed yield of onion (Allium cepa L.). Seed Research. Jaipur India, 180-
182.
 65

Bosch, S. A.D. and Olivé, D.F. 1999. Ecophysiological aspects of nitrogen management in
drip irrigated onion (Allium cepa L). Acta Horticulture, 506:135-140.
Brady, N.C. 1985. The nature and properties of soils. Ninth Edition. Macmillan, New York.
Brewster, J. L. 1990. The influence of cultural and environmental factors on the time of
maturity of bulb onion crops. Acta Horticulture, 267:289-296.
Brewster, J. L. 1994. Onion and other vegetable alliums. CaBI International, Wallingford,
UK.
Bungard, R.A. Wingler, A. Morton, J.D. and Andrews, M. 1999. Ammonium can stimulate
nitrate and nitrite reductase in the absence of nitrate in Clematis vitalba. Plant Cell
Environmet. 22: 859-866.
CIMMYT (International maize and wheat improvement center). 1988. From Agronomic Data
to Farmer Recommendations: An Economics Training Manual. Completely Revised
Edition, DF, Mexico.
Coleo, R.F.V. Souza, A.B. and Conceicao, M.A.F. 1996. Performance of onion crops under
three irrigation regimes and five spacings. Pesquisa Agropecuaria Brasilcira, 31(8):
585-591.
CSA (Central Statistical Agency). 2014. Agriculture Sample Survey. Central Statistical
Agency.Vol.1, Addis Ababa, Ethiopia.
Dawar, N.M. Wazir, F.K. Dawar, M. and Dawar, S.H. 2005. Effect of planting density on the
performance of three varieties of onion under the agro-climatic conditions of
Peshawar. Sarhad Journal of Agriculture, 21:545-550.
Dawar, N.M. Wazir, F.K. Dawar, M. and Dawar, S. H. 2007. Effect of planting density on
growth and yield of onion varieties under climatic conditions of Peshawar. Sarhad
Journal of Agriculture, 23(4):911-918.
Dereje Ademe, Derbew Belew and Getachew Tabor. 2012. Influence of bulb topping and intra
row spacing on yield and quality of some shallot (Allium Cepa Var. Aggregatum)
varieties at Aneded Woreda, Western Amhara, African Journal of Plant Science,
6(6):190-202.
 66

Dorcas, A.O.A. Magaji, M.D. Singh, A. Ibrahim, R. and Siddiqu,Y. 2012. Irrigation
scheduling for onion (Allium cepa L.) at various plant densities in a Semi-Arid
environment. UMT 11th International Annual Symposium on Sustainability Science
and Management, Terengganu, Malaysia.
EARO (Ethiopian Agriculture Research Organization). 2004. Directory of Released Crop
Varieties and their Management. Addis Ababa, Ethiopia.
El-Tantawy, E.M. and El-Beik, A.K. 2009. Relationship between growth, yield and storability
of onion (Allium cepa L.) with fertilization of nitrogen, sulphur and copper under
calcareous conditions. Research. Journal of Agriculture and Biological Science,
5(4):361-171.
Fageria, N.K. and Baligar,V.C. 2005. Enhancing nitrogen use efficiency in crop plants.
Advances in Agronomy, 88(5):97–185.
FAO (Food and Agriculture Organization). 2013. Major food and agriculture commodities and
producers-countries by commodity. www.fao.org.
Ghaffoor, A. Jilani, M.S. Khaliq G. and Waseem, K. 2003. Effect of different NPK levels on
the growth and yield of three onion varieties. Asian Journal of Plant Science, 2
(3):342–346.
Grubben, J.H. and Denton, D.A. 2004. Plant Resources of Tropical Africa. PROTA
Foundation, Wageningen; Backhuys, Leiden, CTA, Netherlands.
Gupta, S.S.S, Gaffer, M.A. 1994. Effect of row spacing and different combination of NPK
fertilizer on the yield of onion. Bangladesh Horticulture, 8:8-12.
Hamasaki, R. Valenzuela, H. and Shimabuku, R. 1999. Bulb Onion Production in Hawaii,
College of Tropical Agriculture and Human Resources (CTAHR), Hawaii, USA.
Hamma, I.L. Ibrahim, U. and Mohammed, A.B. 2013. Growth, yield and economic
performance of garlic (Allium sativum L.) as influenced by farm yard manure and
spacing in Zaria, Nigeria. Agricultural Economic Development, 2(1):001-005.
Hazelton, P. and Murphy, B. 2007. Interpreting Soil Test Results: What do all the numbers
mean? 2nd Edition. CSIRO Publishing, Australia.
Hyder, H. Sharker, N. Ahmed, M.B. Hannan, M.M. Razvy, M.A. Hossain, M. Hoque, A. and
Karim, R. 2007. Genetic variability and interrelationship in onion (Allium cepa L.).
Middle-East Journal of Agricultural Research, 2 (3-4):132-134.
 67

Islam, M.K. Awal, M.A. Ahmed, S.U. and Baten, M.A. 1999. Effect of different set size,
spacing and nitrogen levels on the growth and bulb yield of onion. Pakistan Journal of
Biological Science, 2(4):1146.
Jackson, M.L. 1958. Soil Chemical Analysis. Practice Hall of India, New Delhi.
Jan, N.E. Wazir, F.K. Ibrar, M. Mohammed, H. and Ali, A.R. 2003. Effect of different inter
and intra-row spacing on the growth and yield of different cultivars of onion. Sarhad
Journal of Agriculture, 19:4.
Jilani, M.S. Ghaffoor, A. Waseem, K. and Farooqi, J.I. 2004. Effect of different levels of
nitrogen on growth and yield of three onion varieties. International Journal of
Agriculture and Biology, 6(3):507-510.
Jilani, M.S. 2004. Studies on the management strategies for bulb and seed production of
different cultivars of onion (Allium cepa L.). MSc. dissertation, North West Frotier
Province of Pakistan. Agriculture University, Peshawar, Pakistan.
Jilani, M.S. Khan, M.Q. and Rahman, S. 2009. Planting densities effect on yield and yield
components of onion (Allium cepa L.). Journal of Science Agricultural Researh,
47(4):397-404.
Jilani, M.S. Ahmed, P. Waseem, K. and Kiran, M. 2010. Effect of plant spacing on growth and
yield of two varieties of onion (Allium cepa L.), Pakistan Journal of Science, 62(1):37-
41.
Kabir, M.H. and Sarkar, M.A.R. 2008. Seed yield of mungbean as affected by variety and
plant spacing in Kharif-I season. Journal of Bangladesh Agriculture University.
6(2):239-244.
Kandil, A.A. Sharief, A. and Fathalla, E.F.H. 2013. Effect of organic and mineral fertilizers
on vegetative growth, bulb yield and quality of onion cultivars. ESci Journal of Crop
Production, 2(3):91-100.
Kantona, R.A.L. Abbeyb, L. Hillac, R.G. Tabil, M.A. and Jane, N.D. 2003. Density affects
plant development and yield of bulb onion (Allium cepa L.) in Northern Ghana.
Journal of Vegetable Crop Production, 8(2):15-25.
Khan, H.B. Iqbal, M. Ghafoor, A. and Waseem, K. 2002. Effect of various plant spacing and
different nitrogen levels on the growth and yield of Onion (Allium cepa.L). Journal of
Biological Science, 2(8):545-547.
 68

Khan, M.A. Hasan, M.K. Miah, M.A.J. Alam, M.M. and Masum, A.S.M.H. 2003. Effect of
plant spacing on the growth and yield of different cultivars of onion. Pakistan Journal
of Biological Science, 6(18):1582-1585.
Kokobe Weldeyohanes, Derbew Belay and Adugna Debela. 2013. Effect of farmyard manure
and nitrogen fertilizer rates on growth, yield and components of onion (Allium cepa.L).
at Jimma, South West Ethiopia. Asian Journal Plant Science, 1-6.
Kumar, H. Singh, V.J. Ajay, K. Mahak, S. Kumar, A. and Singh, M. 1998. Studies on the
effect of spacing on growth and yield of onion (Allium cepa L.) cv. Patna Red. Indian
Journal of Agricultural Research, 2:134-138.
Latif, M.A. Choudhury, M.S.H. Rahim, M.A. Hasan, M.K. and Pal, B.K. 2010. Effects of
spacing and age of seedling on the growth and yield of summer onion. Journal of.
Agroforestry and Environment, 3 (2):129-133.
Lemma Dessalegn and Shimeles Aklilu. 2003. Research Experience in Onion Production.
Research Report Number, 55, EARO, Addis Ababa, Ethiopia.
Lemma Dessalegn. 2004. Onion Production Pamphlet (Amharic version). EARO, Melkassa
Research Center, Ethiopia.
Lemma Dessalegn, Shimeles Aklilu, Selamawit Ketema and Chimdo Anchela, 2006. The
Vegetable Seed Sector in Ethiopia: Current Status and Future Prospects. EHSS,
Proceedings of the Inaugural and Third National Horticultural Workshop, Ethiopia.
Volume I. 103-109.
Mahadeen, A.Y. 2008. Effect of planting date and plant spacing on onion (Allium cepa. L)
yield under rain fed in Semi-Arid conditions of Jordan. Bull Faci. Agricultural, 59:
237-241.
Mallor, C. Balcells, M. Sales, E. 2011. Genetic variation for bulb size, soluble solids content
and pungency in the Spanish sweet onion variety Fuentes de Ebro. Response to
selection for low pungency. Plant Breeding, 130:55-59.
Marschner, H. 1995. Mineral Nutrition of Higher Plants, 2nd edition. Academic press,
London, UK, 196p.
Meena, P.M. Vijai, K. Umrao, Amit, K. and Kumar, R. 2007. Effect of nitrogen doses on
growth yield of onion (Allium cepa L.) cv. 'Nasik red'. Journal. Maharashtra
Agriculture University, 9: 53-56.
 69

Mohamed, E.N.M. 1991. Effect of plant population and nutrition on yield and quality of
onion in Kassala, Sudan.
MoARD (Ministry of Agriculture and Rural Development). 2010. Crop variety register.
Ministry of Agriculture and Rural Development. Issue no.13, Addis Ababa.
Morsy, M.G. Marey, R.A. Karam, S.S. and Abo-Dahab, A.M.A. 2012. Productivity and
storability of onion as influenced by the different levels of NPK fertilization. Journal
of Agricultural Research Kafer El-Sheikh University, 38(1):171-186.
Moursy, M.E. Khalifa, H.E. Attia, M.M. Sayed, M.A. and Osman, A.M. 2007. Effect of
organic and nitrogen fertilizers and plant densities on onion production in sandy soils
under drip irrigation system. Alex. Journal Agricultural Research, 52 (1):103-108.
Muhammad, A. Gambo, B.A. and Ibrahim, N.D. 2011. Response of onion (Allium cepa L.) to
irrigation intervals and plant density in Zuru, Northern Guinea Savanna of Nigeria,
Nigerian Journal of Basic and Applied Science, 19(2):241-247.
Murphy, H.F. 1968. A report on fertility status and other data on some soils of Ethiopia.
College of Agriculture HSIU. Experimental Station Bulletin No. 44, Collage of
Agriculture
Naik, B.H and Hosamani, R.M. 2003. Effect of spacing and nitrogen levels on growth and
yield of Kharif onion. Karnataka Journal of Agriculture. Science, 16 (1):98-102.
Nasir, M.D. Faridullah, K.W. Manhaj, U.D. and Shah, H.D. 2007. Effect of planting density
on growth and yield of onion varieties under climatic conditions of Peshawar. Sarhad
Journal of Agriculture, 23 (4):912-918.
Nasreen, S. Haque, M.M. Hoss ain, M.A. and Farid, A.T.M. 2007. Nutrient uptake and yield
of onion as influenced by nitrogen and sulphur fertilization. Bangladesh Journal of
Agricultural Research, 32(3):413-420.
Neeteson, J.J. Booij, R. and Withmore, A.P. 1999. A review on sustainable nitrogen
management in intensive vegetable production systems. Acta Horticulture, 506:17-
26.
Negash Aregay, Mitiku Haile and Yamoah, C. 2009. Growth and bulb yield response of onion
(Allium cepa L.) to nitrogen and phosphorous rates under variable irrigation regimes in
Mekelle, Northern Ethiopia. Journal of the Dry Lands. 2(2):110-119.
 70

Nikus O. and Fikre Mulugeta. 2010. Onion Seed Production Techniques: A Manual for
extension agents and seed producers, FAO‐CDMDP, Asella, Ethiopia.
Olsen, S.R. Cole, C.V. Watanabe, F.S. and Dean, L.A. 1954. Estimation of available
phosphorus in soil by extraction with sodium bicarbonate. USDA, Circular, 939:1-
19.
Rajcumar, R. 1997. Selection of onion cultivars for yield, early maturity and storage potential
in Mauritius. Food and Agricultural Research Council, Reduit, Mauritius. pp.153-159.
Pervez, M.A. Ayub, C.M. Alisaleem, B. Virk, N.A. and Mahmood, N. 2004. Effect of nitrogen
levels and spacing on growth and yield of radish (Raphanus sativus L.). International
Journal of Agriculture and Biology, 6(3):504-506.
Purseglove, J.W. 1985. Tropical crops Monocotyledons. Longman Singapore Publishers,
PTC, Ltd. pp 271-279.
Rabinowitch, H.O. and Currah, L. 2002. Allium Crop Science: Recent Advances.CABI
Publishing, UK. 585p.
Rao, B.N. Roy, S.S. Jha, A.K. Singh, I. M. and Prakash, N. 2013. Influence of nitrogen and
spacing on the performance of Alliuodorosum under mid-altitude foothill condition of
Manipur. Indian Journal of Hill Farming, 26(2):67-70.
Rizk, F.A. Shaheen, A.M. Abd El-Samad, E.H. and Sawan, O.M. 2012. Effect of different
nitrogen plus phosphorus and sulphur fertilizer levels on growth, yield and quality of
onion (AIlium cepa L.). Journal of Applied Science Research, 8(7):3353-3361.
Rubatzky, V.E and Yamagunchi, M. 1997. World Vegetables, Principles, Production, and
Nutritive Value 2nd edition. International Thomson publishing. 804 p.
Rumpel, J. Felc/ynski, K. Stoffella, P.J. Cantliffe, D.J. and Donialo, G. 2000. Effect of plant
density on yield and bulb size of direct sown onions. 8lh int’l. Symposium. on liming
of field prod, in vege. Crops, Bari, Italy. Acta Horticulture. 533:179-185.
SAS Institute Inc, 2004. SAS/STAT. 9.1.3 User’s Guide. Cary, NC: SAS Institute Inc, USA.
Saud, S. Yajun, C. Razaq, M. Luqman, M. Fahad, S. Abdullah, M. and Sadiq, A. 2013. Effect
of potash levels and row spacing on onion yield. Journal of Biology, Agriculture and
Healthcare, 3(16), 2224-3208.
 71

Savva, A. and Frenken, K. 2002. Irrigation Manual Module 3: Agronomic aspects of irrigated
crop production. water resources development and management officers and FAO
Sub-Regional Office for East and Southern Africa, Harare, Zimbabwe.
Sharma, R.P.1992. Effect of planting material, nitrogen and potash on bulb yield of rainy
season onion (Allium cepa L.). Indian Journal of Agronomy, 37:868-869.
Seck, A. and Baldeh, A. 2009. Studies on onion bulb yield and quality as influenced by plant
density in organic and intensive cropping systems in The Gambia (West Africa).
African Crop Science Conference Proceedings, 9:169 -173.
Seid Hussena, Fikrte Medhinbs, Abeba Tadesse. 2014. Effect of intra-row spacing on growth
performance of garlic (Allium sativum) at the experimental site of Wollo University,
South Wollo, Ethiopia. European Journal of Agriculture and Forestry Research,
2(4):54-61.
Sikder, M. Mondal, F. Mohammed, D. Alam, M.S. and Amin, M.B. 2010. Effect of spacing
and depth of planting on growth and yield of onion. Journal of Agroforestry
Environment, 4 (2):105-108.
Silvertooth, C. J. 2001. Row spacing, plant population, and yield relationships. Internetdo
ument. http://cals.arizona.edu/crop/cotton/comments/aprill999cc.html.
Smith, L. and Hamel, C. 1999. Crop yield: Physiology and processes. Springer-Verlag, Berlin
Heidelberg, Germany.
Shojaei, H. Vakili, S.M.A. Khodadadi, M. Mirzae, Y. 2011. Effect of different N fertilization
levels and plant population on agronomic traits and decrease in bolting of autumn-
sown onion in Shahdad Region of Kerman. Iran. Plant Ecophysiology, 3(2011):59-64.
Soleymani, A. and Shahrajabian, M. H. 2012. Effects of different levels of nitrogen on yield
and nitrate content of four spring onion genotypes. International Journal of
Agricultural Crop Science, 4 (4):179-182.
Sørensen, J.N. and Grevsen, K. 2001. Sprouting in bulb onions (Allium cepa L.) as
influenced by nitrogen and water stress. Journal of Horticultural Science and
Biotechnology, 76:501-506.
Soujala, T.T. Salo T. and Pessala, R. 1998. Effect of fertilization and irrigation practices on
yield, maturtity and storability of onions. Agricultural and Food Science in Finland,
7:477- 489.
 72

Stoffela, P.J. 1996. Planting arrangement and density of transplants influence sweet Spanish
onion yields and bulb size. Horticultural Science, 317:1129-1130.
Tekalign Tadese. 1991. Soil, plant, water, fertilizer, animal manure and compost analysis.
Working Document No. 13. International Livestock Research Center for Africa, Addis
Ababa, Ethiopia
Tekalign Tsegaw, Abdissa Yohanes and Pant, L.M. 2012. Growth, bulb yield and quality of
onion (Allium cepa L.) as influenced by nitrogen and phosphorus fertilization on
Vertisol II: Bulb quality and storability. African Journal of Agricultural Research,
7(45):5980-5985.
UAAE (Upper Awash Agro-Industry Enterprise). 2001. Progress Report 1996-2002, Addis
Ababa, Ethiopia. Agricultural product 2001/2002, Addis Ababa, Ethiopia.
Walkley, A. and Black, C.A. 1934. Determination of organic matter in the soil by chronic acid
digestion. Soil Science, 63:251-264.
Ware, G.W. and McCollum, J.P. 1980. Producing Vegetables Crops, Interstate Press,
Danville, IL, USA.
Waskar, D.P. Khedkar, R.M. Garande, V.K. 1999. Effect of post-harvest treatments on shelf
life and quality of pomegranate in evaporative cool chamber and ambient conditions.
Journal of Food Science Technology, 36(2), 114-117.
Yadav, R.L. Sen, N.L. and Yadav, B.L. 2003. Response of onion to nitrogen and potassium
fertilization under semi-arid condition. Indian Journal Horticulture, 60(2):176-178.
Yamasaki, A. and Tanaka, K. 2005. Effect of nitrogen on bolting of bunching onion (Allium
fistulosum L). Horticulture Research (Japan), 4(1):51-54.
Yemane Kahsay, Derbew Belew and Fetien Abay. 2013. Effect of intra-row spacing on yield
and quality of some onion varieties (Allium cepa L.) at Aksum, Northern Ethiopia.
African Journal of Plant Science, 7(12):613-622.
Yemane Kahsay, Derbew Belew and Fetien Abay. 2014. Effect of intra-row spacing on plant
growth and yield of onion varieties (Allium cepa L.) at Aksum, Northern Ethiopia.
African Journal of Agricultural Research, 9 (10):931-940.
 73

7. APPENDICES

Appendix Table 1. Mean squares of analysis of variance for leaf length (LL), leaf diameter
(LD), plant height (PH), leaf number per plant (LN), bolting percentage (BP) and stand count
percentage (SCP)

Source Degree
of variation of Mean square values
Freedom LL LD PH
LN SCP BP
Replication 2 2.81 0.0002 0.069 2.28 1.93 11.46
N level 3 158.07** 0.551** 29.54** 383.18** 10.26** 719.42**
Spacing 4 79.97** 0.434** 21.75** 109.41** 785.64** 416.62**
Spacing*N 12 16.46** 0.010** 1.30** 3.60ns 1.33ns 15.12**
Error 38 1.79 0.001 0.338 8.84 0.700 2.46
CV (%) 4.38 3.31 6.62 6.98 0.93 9.93
ns=non-significant, * and ** indicates significant difference at probability levels of 5% and
1%, respectively

Appendix Table 2. Mean squares of analysis of variance for yield and yield related traits of
onion

Source of Degree
Variation of Mean square values
Freedom ABW ND BD UBY MBY TBY
Replication 2 15.73 0.001 0.009 0.006 0.289 0.226
N level 3 9918.18** 0.53** 11.28** 4.39** 443.31** 364.32**
Spacing 4 2844.77** 0.20** 7.58** 3.76** 200.12** 184.69**
Spacing*N 12 177.19** 0.01** 0.189** 0.31** 27.31** 28.45**
Error 38 13.03 0.001 0.013 0.004 0.451 0.453
CV (%) 5.66 3.97 2.60 10.00 2.61 2.55
* and ** indicates significant difference at probability levels of 5% and 1%, respectively ,
ABW = Average bulb weight; BD = Bulb diameter; TBY = Total bulb yield; ND = Neck
diameter; MBY = Marketable bulb yield; UBY = Unmarketable bulb yield
 74

Appendix Table 3. Mean squares of analysis of variance for marketable and unmarketable size
distribution of onion

Source of Degree
Variation of Mean square values
Freedom SSB MSB LSB OSB USB
Replication 2 0.013 0.237 0.012 0.005 0.004
N level 3 106.63** 432.63** 103.63** 9.96** 2.41**
Spacing 4 135.91** 192.79** 38.82** 4.84** 2.98**
Spacing*N 12 1.55** 20.90** 7.01** 1.09** 0.37**
Error 38 0.256 0.324 0.072 0.007 0.002
CV (%) 8.63 3.59 6.69 9.61 10.35
* and ** shows significant difference at probability levels of 5% and 1%, respectively, SSB =
Small sized bulb, MSB = Medium sized bulb, LSB = Large sized bulb, OSB = Oversized bulb
and USB = Under sized bulb

Appendix Table 4. Mean squares of analysis of variance for Shoot dry matter per plant
(SDMY), Harvest index (HI), Dry total biomass (DTB), Total soluble solids (TSS), Days to
maturity (DTM) and Bulb dry matter yield per plant (BDMY)

Source Degree of
of variation Freedom Mean square values
SDMY BDMY DTB TSS DTM HI
Replication 2 0.002 0.009 0.007 0.01 2.40 0.88
N level 3 4.48** 69.18** 108.72** 5.61** 731.12** 40.98**
Spacing 4 4.76** 44.02** 77.37** 12.04** 296.56** 8.36**
Spacing*N 12 0.24** 2.64** 4.32** 0.13** 14.89** 3.38**
Error 38 0.006 0.028 0.043 0.028 4.33 0.93
CV (%) 4.27 3.00 2.85 1.43 1.86 1.27
* and ** indicates significant difference at probability levels of 5% and 1%, respectively
 75

Appendix 5. Simple correlation between yield, yield components and growth characters

Variables SBS MBS LBS MY UMY TY OBS USB BP SCP LN PH

SBS 1.00
MBS -0.67** 1.00
LBS -0.85** 0.80** 1.00
MY -0.45** 0.95** 0.74** 1.00
UMY 0.89** -0.76** -0.75** -0.56** 1.00
TY -0.37** 0.91** 0.70** 0.99** -0.46** 1.00
OBS -0.74** 0.36** 0.71** 0.24ns -0.57** 0.19ns 1.00
USB 0.85** -0.72** -0.66** -0.50** 0.98** -0.41** -0.50** 1.00
BP 0.88** -0.59** -0.81** -0.43** 0.79** -0.36** -0.78** 0.74** 1.00
SCP -0.82* 0.29* 0.54** 0.06ns -0.67** -0.03ns 0.56** -0.66** -0.65** 1.00
LN -0.88** 0.66** 0.88** 0.53** -0.78** 0.47** 0.84** -0.72** -0.81** 0.69** 1.00
PH -0.81** 0.69** 0.79** 0.56** -0.79** 0.50** 0.72** -0.73** -0.80** 0.52** 0.84** 1.00
LL -0.82** 0.62** 0.76** 0.47** -0.82** 0.40** 0.63** -0.75** -0.81** 0.55** 0.75** 0.81**
LD -0.93** 0.61** 0.87** 0.45** -0.84** 0.37** 0.87** -0.77** -0.88** 0.75** 0.94** 0.84**
BD -0.93** 0.64** 0.87** 0.47** -0.85** 0.40** 0.82** -0.78** -0.91** 0.74** 0.91** 0.84**
ND -0.86** 0.59** 0.85** 0.46** -0.75** 0.40** 0.88** -0.68** -0.88** 0.60** 0.89** 0.86**
ABW -0.85** 0.63** 0.86** 0.50** -0.76** 0.44** 0.91** -0.68** -0.88** 0.58** 0.91** 0.86*
BDW -0.92** 0.68** 0.93** 0.55** -0.77** 0.49** 0.86** -0.70** -0.88** 0.71** 0.94** 0.84**
DTM -0.88** 0.58** 0.84** 0.43** -0.77** 0.36** 0.88** -0.70** -0.88** 0.63** 0.85** 0.83**
SDW -0.90** 0.54** 0.86** 0.39** -0.74** 0.32* 0.89** -0.67** -0.88** 0.78** 0.92** 0.80**
HI -0.48** 0.83** 0.69** 0.84** -0.55** 0.83** 0.27* -0.47** -0.43** 0.04ns 0.51** 0.56**
DTB -0.92** 0.65** 0.92** 0.52** -0.77** 0.46** 0.88** -0.69** -0.89** 0.73** 0.94** 0.83**
TSS 0.34** 0.26* 0.02ns 0.46** 0.1ns 0.51** -0.14ns 0.20ns 0.14ns -0.77** -0.19ns 0.002ns
*, ** and ns indicates that significant, highly significant and non-significant difference at probability levels of 5% and 1%, respectively
and SBS, MBS, LBS, MY, UMY, TY, OBS, USB, BP, SCP, LN and PH= Small sized bulb, Medium Sized bulb, Large sized bulb,
Marketable yield, Unmarketable yield, Total yield, Oversized yield, Under sized yield, Bolting percentage, Stand count percentage,
leaf number per plant and Plant height respectively.
 76

Appendix 5. Simple correlations (CONTINUED)

Variables LL LD BD ND ABW BDW DTM SDW HI DTB TSS

LL 1.00
LD 0.83** 1.00
BD 0.83** 0.97** 1.00
ND 0.79** 0.93** 0.92* 1.00
ABW 0.79* 0.95** 0.94** 0.95** 1.00
BDW 0.77** 0.96** 0.94** 0.94** 0.94** 1.00
DTM 0.79** 0.92** 0.91** 0.92** 0.92** 0.91** 1.00
SDW 0.73** 0.96** 0.94** 0.93** 0.93** 0.98** 0.90** 1.00
HI 0.53** 0.45** 0.48** 0.50** 0.50** 0.53** 0.44** 0.34** 1.00
DTB 0.76** 0.97** 0.95** 0.94** 0.94** 0.99** 0.91** 0.99** 0.49** 1.00
TSS -0.07ns -0.25ns -0.21ns -0.08ns -0.02ns -0.18ns -0.11ns -0.31* 0.40** -0.21* 1.00
LL, LD, BD, ND, ABW, BDW, DTM, SDW, HI, DTB ant TSS= Leaf length, Leaf diameter, Bulb diameter, Neck diameter, Average
bulb weight, Bulb dry weight, Days to maturity, Shoot dry weight, Harvest index, Dry total biomass and Total soluble solids
respectively