SUGAR MILLING RESEARCH INSTITUTE

TEN WEEK COURSE IN SUGAR ENGINEERING

SUGARCANE AGRICULTURE

SUGAR MILLING RESEARCH INSTITUTE

UNIVERSITY OF KWAZULUNATAL
4041 DURBAN
SOUTH AFRICA

These notes are exclusively for use in sugar technology courses

run by the Sugar Milling Research Institute and may not be reproduced without the
permission of the Institute.
 TABLE OF CONTENTS

Course outcomes .................................................................................................................. i

1. Some Basic Facts ..................................................................................................................1

1.1 Geographic Distribution of Cane .................................................................................1
1.2 C4 vs C3 Plants ...........................................................................................................1
1.3 Yields ...........................................................................................................................1
1.4 Employment .................................................................................................................1

2. The Sugarcane Plant .............................................................................................................2

2.1 The raw materials .......................................................................................................2
2.2 The Products ...............................................................................................................2
2.3 Assessment of performance ...................................................................................... 3
2.3.1 The quality and quantity of raw materials ....................................................... 3
2.3.2 Product quality ................................................................................................. 3
2.4 Hazards to Production ................................................................................................ 4

3. Terminology ........................................................................................................................... 4

4. The Structure and Physiology of The Sugarcane Plant .................................................... 5

4.1 Structure ...................................................................................................................... 5
4.1.1 The stalk .......................................................................................................... 5
4.1.2 The leaf ............................................................................................................ 5
4.1.3 The root system ............................................................................................... 6
4.1.4 The inflorescence ............................................................................................ 7
4.2 Propagation and Growth.............................................................................................. 7
4.2.1 Apical dominance ............................................................................................ 9
4.2.2 Sanitation of setts ............................................................................................ 9
4.2.3 Sett development ............................................................................................. 9
4.2.4 Ratooning......................................................................................................... 9
4.2.5 Growth Phases ................................................................................................ 9

5. Sugarcane Varieties : History and Breeding .................................................................... 10

5.1 History ........................................................................................................................ 10
5.1.1 Uncontrolled introduction of varieties ............................................................ 10
5.1.2 Controlled introduction of varieties ................................................................ 11
5.1.3. Introduction of true sugarcane seed.............................................................. 11
5.1.4. Sugarcane breeding in KwaZuluNatal ........................................................... 12
5.1.5 Sugarcane Varieties in KwaZuluNatal ........................................................... 12
5.1.6 Variety Nomenclature .................................................................................... 13
5.2 Breeding new varieties
5.2.1 Objectives of the breeding programme ......................................................... 13
5.2.2 How difficult is it to find new varieties? .......................................................... 13
5.2.3. Crossing ......................................................................................................... 14
5.2.4 Seedlings ....................................................................................................... 14
5.2.5 Selection procedure ....................................................................................... 15

6. Soils....................................................................................................................................... 15
6.1 Nature and distribution of soils .................................................................................. 15
6.2 Physical and chemical characteristics....................................................................... 16
6.2.1 Grey Soils ...................................................................................................... 16
 ii

6.2.2 Black Soils ..................................................................................................... 16

6.2.3 Red Soils........................................................................................................ 16
6.2.4 Brown humic soils .......................................................................................... 16
6.3 Some implications of soil characteristics .................................................................. 17

7. Land Preparation ................................................................................................................. 18

7.1 Killing the old crop ..................................................................................................... 18
7.1.1 Mechanical ..................................................................................................... 18
7.1.2 Chemical ........................................................................................................ 18
7.2 Minimum tillage .......................................................................................................... 19

8. Planting ................................................................................................................................. 20
8.1 The planting season ................................................................................................. 20
8.2 Planting methods ....................................................................................................... 20

9. Nutrition and Fertilizers ...................................................................................................... 21

9.1 Inorganic Fertilizers ................................................................................................... 21
9.1.1 Nitrogen carriers ............................................................................................ 21
9.1.2 Phosphate ...................................................................................................... 22
9.1.3 Potassium ...................................................................................................... 22
9.1.4 Mixtures ......................................................................................................... 22
9.2 Organic Manures ....................................................................................................... 22
Filter cake ................................................................................................................. 23
9.3 Fertilizer Advisory Service (FAS) .............................................................................. 25

10 Harvesting ......................................................................................................................... 25
10.1 Comparison of trashing with burning ....................................................................... 25
10.2 Codes of burning practice ........................................................................................ 27

11 Cane growth on stream banks and wetlands ................................................................. 27

12 Costs of production ........................................................................................................... 27

 COURSE OUTCOMES

At the end of this course you should be able to answer the following questions, or fulfill the role
indicated in the questions:

1. Imagine that you are a mill manager. New and inexperienced growers have acquired farms in
your area and have asked you to give them a short course on how they should go about
growing cane and ensuring maximum payment for what they produce. In particular they want
you to explain the cane payment system and how it affects the management of their
operations. (Assume that the cane payment system is broadly similar to the South African
ERC system). Prepare brief notes for use as a memory-aid during your lectures.

2. At a forthcoming meeting of a Mill Group Board (Note: each mill has a Mill Group Board as a
means of liaison between millers and growers) one of the agenda items is:

“Filtercake – growers’ concerns regarding decreased quantity and quality”.

You, as a miller representative, are aware that the background to this item is the fact that the
growers have been told that your mill is keen to recycle filter cake to the diffuser. The Board
Chairman has asked you to present to the meeting an honest overview of the value (to
growers) of filter cake, and the consequences of returning it to the diffuser. Your mill has wet
scrubbers and will continue to produce fly ash.

You have time for 6-8 Powerpoint slides. Sketch the wording you would have on the slides,
and write some speaker notes for each slide.

3. You are a mill engineer and, for the first time, you have been invited to the annual cocktail
party for growers and millers in your area. Your boss suggests that you need to get to know
some of the farmers and it will be helpful if you know their favourite discussion topics. He
gives you the following hints and suggests that you prepare yourself to be able to hold a
knowledgeable discussion on each of the topics with the person concerned.

Mr RV Maker - issues around measurement of RV at the mill and why his cane is
usually below average RV. Why can’t payment be simply based on tons pol
delivered.

Mr Staywell Dlamini - why don’t millers and growers work together in ensuring
proper establishment of the crop and some sort of collaborative harvesting,
including ripening?

Mrs “Hilly” Competence - has a special interest in cane breeding and in proper
nutrition of cane. One of her sons believes that they should buy another cane farm
but in an African country where the natural resources are better for cane growing.

Prepare some notes for yourself to read immediately before going to the party. Assume that
you are confident that you can avoid one of the people (your choice) so you need prepare for
only two of the discussions.
 1

SUGAR CANE AGRICULTURE

1. SOME BASIC FACTS

1.1 Geographic Distribution of Cane

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Transkei at 35 S is the most southerly in the world.
0

Pakistan, Egypt, Louisiana (USA) and Japanese islands at 32 N are most northerly.
0

Best below about 25 - in Transkei the warm Mozambique current facilitates the growth.
0

(Sugar beet prefers cooler climate, usually >35 N or S).

1.2 C4 vs C3 Plants

Cane has a “C4” photosynthetic pathway whereas beet has “C3”.

The C4 system is adapted to high sunlight and under such conditions it is much more
efficient than C3, leading to faster growth with better uptake of CO2 - if a C4 and C3 plant
are put together in a sealed system the C3 plant dies because the C4 plant uses up the
CO2 preferentially, eventually assimilating the C3 plant as it decays).

1.3 Yields

Note that there are two methods of expressing yields and these often lead to confusion:

(a) t / ha harvested
(b) t / ha / annum (i.e. the yield of a 24 month crop is divided by 2)

In South Africa the range is from about 40 to 150 t I ha / an with an average of 54. The higher
yields are achieved with irrigation and because surrounding countries use much irrigation their
average yields are higher than in SA. Only 21% of the SA crop is irrigated.

Australian yields are 65 t I ha / an. In Colombia - 1t sugar / ha / month (i.e. about 100t/ha/an).

The theoretical maximum yield, based on radiation, is 193 t / ha / an.

The SA crop of about 2,2 m tons of sugar (2% of the worlds total) comes from 412 000 ha of
cane. About 68% of this is within 30 ha of the coast.

1.4 Employment

In SA there are more than 50 000 registered growers of which about 48 000 are small scale
growers (producing less than 150 t sucrose / an). The industry employs about 85000 people,
mostly in agriculture. Indirect employment accounts for a further 143 000 jobs, and it is
estimated that almost one million people are dependent on the sugar industry. It is an industry
which is expanding in other African countries, where it also provides significant employment.

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2. THE SUGARCANE PLANT

If you want to remain in an engineering frame of mind, rather than an agricultural one, then
simply regard the sugarcane plant as a factory and draw some analogies with what you know
about sugar factories.

2.1 The raw materials

(a) Sun (energy) (b) CO2 (c) water (d) nutrients

2.2 The Products (i.e. harvested cane)

Component Unburnt Burnt Unburnt Burnt

topped topped untopped untopped

% wet mass
90.3 96.8 77.8 91.2
Stalk

Tops 2.8 2.7 14.3 8.3

Trash 6.9 0.5 7.9 0.5

% dry mass
80.5 96.1 66.2 88.6
Stalk

Tops 1.8 2.4 13.0 9.8

Trash 17.6 1.4 20.8 1.4

% wet mass
11.53 13.57 10.63 13.39
Pol

Brix 13.61 15.35 13.23 15.5

Purity 84.63 88.4 80.36 86.37

Moisture 65.16 70.25 65.48 69.82

Fibre 21.22 14.40 21.58 14.68

Ash 2.48 1.13 2.76 2.11

In addition, the root mass is about 40% of the total.

2.3 Assessment of performance

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2.3.1 The quality and quantity of raw materials used by the sugarcane plant - What can the farmer
do to influence them? (Make your own notes from the lecture discussion):

(a) Sunlight
C4 plant, therefore tropical. Overcast coastal conditions sometime cause reduced
growth.

(b) Carbon dioxide

Needed for C in sugar.
Biofuels and global warming:

(c) Water
An increasingly limiting resource.
Quantities required:

(d) Nutrients
Examples of N, P & K applications {Perspective: N, P,K = 120, 30, 125 kg/ha)
Dependent on soil type and expected growth.
High cost. Potential for re-cycling.

2.3.2 Product quality

Estimated recoverable sucrose (ERC) is a quality parameter.

ERC = aS - bN - cF

Where S = sucrose % cane; N = non-sucrose % cane ; F = fibre % cane, and “a”, “b” and “c”
are factors based on past industrial averages and are about 0,98; 0,53 and 0,018.[Factor ‘c’
implies that for every 1% of fibre in cane, the recoverable sucrose % cane will drop by 0.018
units – the fibre carries this sucrose to bagasse. Factor ‘a’ accounts for undetermined loss and
loss in filter mud. Factor ‘b’ accounts for loss to molasses].

When molasses revenue is also taken into account we talk about Recoverable Value (RV) and
factor ‘b’ is then modified (decreased) to take into account the value of molasses. The formula
gives an answer similar to the formula used in Colombia for cane payment - i.e. S - 0.33N.

The RV formula is currently used for cane payment in South Africa. It requires the input of
molasses and sugar prices, and because these vary from year to year the formula is not
suitable as a selection criterion for cane breeding. ERC is used for this purpose.

Note that the ERC formula reflects sugar revenue rather than profit. The low factor
applicable to fibre is low because of previous high expenditure to achieve high extraction in
South Africa. (What would the factor be if extraction was 93%?). Ideally, the quality formula
should take into account the cost of achieving a particular revenue (i.e. profit). This might then
affect the design of extraction and recovery equipment but, in general, maximum overall
recovery gives maximum profit.

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Factors affecting quality include:

Climate

Variety

Ripeness (and ripeners)

Deterioration (due to delays or pests and diseases)

Harvesting method (tops and trash removal)

Loading method (sand inclusion).

2.4 Hazards to Production

Bacteria - RSD etc

Fungi - smut etc
Viruses - mozaic etc
Phytoplasma - yellow leaf syndrome etc
Nematodes- general yield decline
Weeds - competition for sun and nutrients
Noxious materials - Ca excess, Al, salinity
Drought
Frost
Accidental fires.

3. TERMINOLOGY

If you do not already know the meaning of the following terms then make notes:

Sett Flood irrigation

Ratoon Drip irrigation

Plant cycle Minimum tillage

Overhead irrigation “Fusilade”

“Roundup” RSD

Mozaic Red rot

Smut “Temik”

Hot water treatment Eldana saccharina

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Fuzz Speedling

Breaking point NCo

Strip farming Apical dominance

C4 plant Seedcane

Leaf sheath FAS

FRS Mineralisation

Biocontrol Mancozeb

Waterway 3:1:1 (47)

Chlorosis Top-dressed

Drying off Windrow

YLS “Arrowing”

Bt (Bacillus thuringiensis)

4. THE STRUCTURE AND PHYSIOLOGY OF THE SUGARCANE PLANT

Introduction

Sugarcane is a grass of the Saccharum species. It provides more than 65 % of the world’s
sugar, and is adapted to a wide range of soils and growth conditions. Physiologically it is
unusual in that it produces sucrose as the main photosynthate and stores this, mainly in the
stalk/stem.

4.1 Structure

4.1.1 The stalk

The stalk is divided into nodes and internodes. A leaf arises at each node and there are root
primordia at each node. The primordia develop into roots if the stalk is buried. The length of the
internodes is affected by their growth rate - hence short internodes are produced during slow
winter growth, and a single stalk may have short and long internodes. The thickness of the
stalk is influenced by growth conditions and variety.

The shape and colour of internodes is used in variety identification. There are four main
shapes: cylindrical, barrel-shaped, bobbin-shaped and zig-zag.

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There is normally one bud at each node. The size and shape of the buds is a variety
characteristic.

At the top of each internode there is a light coloured ring called the wax band.

4.1.2 The leaf

See diagram below

Trash is formed when leaves die. In most varieties the leaf blade is shed leaving the sheath as
adhering trash. Self-trashing varieties in which the sheath is also shed are being bred and will
be particularly important where burning is prohibited.

4.1.3 The root system

Extensive studies have been done in the root laboratory at SASRI.

See the diagram and note that there are different types of root. Some varieties are prone to
lodging because of the inadequate root system, particularly buttress roots.

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4.1.4 The inflorescence

Flowering occurs only under certain daylength and temperature conditions. It is not inevitable
and is infrequent in KwaZuluNatal. Fertile seed is not produced under natural conditions in
South Africa, mainly because the pollen is infertile due to imperfect daylength and temperature
combinations. The flowers look like arrows.

4.2 Propagation and Growth

Vegetative propagation from pieces of stalk (setts) is easy and is used for all commercial
production. Think of the consequences of this cloning, linked with long plant cycles:

genetic uniformity - disease susceptibility

long plant cycles - slow response to needs for change
critical need for a breeding programme/biotechnology
convenience of similarity between individual plants for mechanical harvesting etc
ease of stealing varieties.

Note the contrast with sugar beet, which is an annual crop grown from seed.

4.2.1 Apical dominance

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Development of roots and shoots from internodes is suppressed by hormones from near the
growing point of the stem, i.e. the apical portion. In propagating cane it is therefore necessary
to cut off the top of the stalk, not simply to bury stalks. In practice the stalks are normally cut
into short lengths of 2-3 internodes.
Frost can kill the tops of stalks thus removing apical dominance and resulting in formation of
numerous shoots from the stem. Eventually these shoots impose apical dominance. Flowering
also removes apical dominance, and leads to shoot formation.

“Speedlings” are produced by cutting out the bud with only a small amount of associated stem.
This completely removes apical dominance and results in good “germination” but the small
“setts” have to be nursed to prevent moisture stress.

4.2.2 Sanitation of setts

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Before planting, setts should be heated in water at 50 C to kill the bacteria which cause ratoon
stunting disease (RSD). Fungicide is often added to the water to give some protection to the
germinating sett.

The heat treatment destroys hormones which cause apical dominance thus making it possible
to plant whole stalks.

4.2.3 Sett development

The primary shoot gives rise to secondary shoots from buds at its base. These are so-called
tillers and about 30% of them eventually die but good tillering is important for eventual high
yields. Tillering usually ceases after about four months. The clump of shoots is called a stool.

4.2.4 Ratooning

After cane is harvested the old root system supports new growth from the bases of the
remaining stalks. The old roots soon die and are replaced by new roots from the developing
ratoon. Harvesting practices can influence ratooning, e.g. heavy transport damages stools, as
does cutting too low or too high. For best ratooning cane needs to be cut at or just below
ground level. This results in soil and some fine roots being delivered to the mill, i.e. high ash in
cane. (Note the conflict between growers and millers’ interests).

Some varieties ratoon much better than others so in assessing varieties it is necessary to
measure yields over at least two ratoons.

With good management we are able to achieve 8 - 10 ratoons in South Africa. Some countries
achieve only two before yields decline severely. In Colombia there are fields which have been
ratooned more than 20 times and are still highly productive.

4.2.5 Growth Phases

Stalk elongation rate is a good indication of growth rate when good growing conditions prevail
but it is misleading under stress conditions or when the cane is approaching maturity. Under

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these conditions there may be an increase in mass without concomitant elongation of stalk.

There are five phases of growth recognised by agronomists:

Germination - up to the time of rapid tillering

Juvenile - until full ground cover is achieved

Early adult - the period of maximum stalk elongation

Late adult - characterised by a marked decline in growth rate

Flowering - Flower initiation takes place when daylength is 12,5 hours, i.e. 8 - 30 March
in South Africa. Flowering will generally not take place if night temperatures are below
0
21 C or if there is stress. Extensive flowering takes place only about once in five years
in South Africa.

When a cane stalk produces flowers the apical meristem (growing point) changes to
reproductive tissue. The sucrose content of the stalk peaks but if the flowering stalk does not
produce sideshoots then the sucrose content eventually declines rapidly because stalks
without sideshoots die. Sideshoots may not form due to drought or Eldana infestation.
Flowered cane without sideshoots should be harvested before October to avoid sucrose
decline. Crops with less than 20% flowered stalks can be considered as non-flowering.

After flowering is initiated no further internodes are formed. The internode formation normally
takes place in the first five months of growth so if flowering is initiated in young cane the stalks
will be short because of the low number of internodes.

Stalk elongation consists of growth in length of internodes, not growth in number. Hence
severely droughted cane has very short internodes and a small internode:node ratio thus
affecting milling characteristics (tends to “pulp” rather than shred, and has a high bagacillo
ratio).

During rapid growth a relatively high portion of the sugar exists as invert (glucose and fructose)
so immature, growing cane is characterised by low purity. Ripening can be forced by applying
chemicals or by stopping irrigation - this causes the plant to convert invert sugars to sucrose.
Low temperature also causes ripening, hence the highest sucrose content is in mid-winter.

Poor germination has long-term effects on yield because of the reduced plant population,
which extends to subsequent ratoons.

The growth cycle may take only 10 months under ideal growing conditions such as the warm
irrigated northern areas, or it may take 24 months in the rain-fed, colder southern areas.

5. SUGARCANE VARIETIES : HISTORY AND BREEDING

5.1 History

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There seems to have been some sugarcane in KwaZuluNatal in early Zulu history. It was
grown by the local inhabitants for chewing and there was no attempt at making sugar. The
history of sugarcane varieties can be divided into four phases:

5.1.1 Uncontrolled introduction of varieties

Until about 1914, sugarcane for planting could be introduced without control, and no quarantine
measures were applied. It is not surprising therefore that a number of diseases, such as
mosaic and smut, and also pests, were introduced.

By 1880, commercial canes included “Green Natal” (which later became infected with mosaic)
and “China Cane” (which became infected with smut).

Between 1883 and 1885, Uba was introduced. This was not a very productive cane and was
medium to low in sucrose content. In the factory it was poor - being tough and fibrous. Growers
liked it because of its disease resistance, especially to mosaic. It stooled easily and could give
many ratoons, and was resistant to frost and drought. For about fifty years the South African
sugar industry depended almost exclusively on Uba. Later this variety became infected with
streak disease.

Many other varieties were introduced and tried, first by private growers and companies, later by
the Natal Department of Agriculture. This led to the second phase, that of controlled
introduction.

5.1.2 Controlled introduction of varieties

In the early 1900’s the Department of Agriculture started making rules for the introduction of
sugarcane for planting, and co-operation between the newly-formed Sugar Association and the
Government led to the establishment of quarantine stations in which potential new varieties
could be tested.

By 1924 mosaic disease was prevalent in practically all varieties except Uba, and strict control
of importations was enforced. This was made easier by the building of a quarantine
glasshouse in Durban in 1925.

The Experiment Station was started in 1925, and its main function was the introduction and
testing of new varieties following the total infection of Uba with streak disease. During the next
ten years the following varieties were released for general propagation:

POJ2714, 2725, 2727, 2878 from Java, and

Co281, 290, 301, 331 from India.

Although some of these were successful here, it became apparent that varieties which grew
very well in other countries were not always suited to South African conditions. Of the above
varieties, several became infected with diseases, for example, Co290 with red rot, and Co28l
with ratoon stunting disease. In 1932 a start was therefore made with the introduction of

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sugarcane seed.

5.1.3. Introduction of true sugarcane seed

Sugarcane had never been known to produce seed under South African conditions and it was
assumed that it could not do so. As a substitute, cane breeding stations in various countries
overseas were asked to cross selected sugarcane varieties and to send the resulting seed to
SA. From the offspring, varieties suited to local conditions were selected. The most successful
batches of seed came from Coimbatore in India, and gave rise to the NCo canes of which
NCo292, 293, 310, 334, 339, 376 and NCo382 were released. Of these, NCo310 and NCo376
are excellent varieties and were grown in a number of other countries as well as South Africa.
In the meantime factors concerned with the fertility of sugarcane flowers were studied.

5.1.4. Sugarcane breeding in KwaZuluNatal

The reason for the inability of sugarcane grown in South Africa to set viable seed is the
infertility of the pollen, brought about by the low night temperatures. However, the female part
of the flower is less sensitive and fertile ovules are produced.

In 1944, however, some fertile seed was found in the field and the next year the first artificial
crosses were made. It was found that, by keeping flowers of varieties in a heated glasshouse
they could produce viable pollen. This, and the development of a technique for growing cut
flowering stems in the glasshouse, led to the production of new varieties bred wholly in
KwaZuluNatal. The first of these, N50/211, was released in 1959.

A further refinement of the procedure has been brought about by the use of a photoperiod
house. This is used to alter the day length from that occurring naturally in KwaZuluNatal, to one
that is more conducive to flower induction. It is used to produce flowers from shy-flowering
varieties, as well as to synchronize the flowering of specific varieties so that they may be
crossed.

5.1.5 Sugarcane Varieties in South Africa

It is illegal to plant varieties which have not been approved. Unapproved varieties may be
dangerous because they may be susceptible to disease and become foci for dissemination of
the disease. Some varieties are approved only for certain areas because they are susceptible
to diseases which are not problematic in these areas, e.g. smut-prone varieties can only be
grown in the South where smut is not a problem. The approved varieties are listed annually in
the Government Gazette.

Of the old varieties, only Co331 is still on the list of approved varieties.

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5.1.6 Variety Nomenclature

Variety prefix Country of origin

B ................................................................................................................................. Barbados
CB ..................................................................................................................................... Brazil
Co.................................................................................................................. Coimbatore, India
CP .............................................................................................................. Canal Point, Florida
F .................................................................................................................................. Formosa
ROC ............................................................................................................................... Taiwan
H...................................................................................................................................... Hawaii
L ................................................................................................................................. Louisiana
M ................................................................................................................................. Mauritius
N................................................................................................................. Natal (South Africa)
NA .............................................................................................................................. Argentina
NCo ................................................Selected in Natal from seed sent from Coimbatore, India
Ni ...................................................................................................................................... Japan
NiN ...................................................................................... (Selected from Natal seed) Japan
POJ .................................................................................................................................... Java
Q ............................................................................................................................ Queensland
R................................................................................................................................... Reunion
SP, RB .............................................................................................................................. Brazil
Triton, etc ......................................................... (Colonial Sugar Refining Co, NSW, Australia)
Named after characters in Greek mythology

5.2 Breeding New Varieties

5.2.1 Objectives of the breeding programme

These can be stated simply:

To produce the most profitable sugarcane varieties for our conditions in terms of recoverable
sugar per hectare and adequate resistance to important diseases and pests.

5.2.2 How difficult is it to find new varieties?

The task is particularly difficult because a plant does not perform equally well on different sites
nor during different seasons. Varieties also differ in their ratooning abilities. The relative
performance of different varieties can therefore be assessed only approximately over a
prolonged series of comparative tests.

The task is complicated because a large number of characteristics have to be studied. Some
of these are:
Total yield of recoverable sugar per hectare
ERS content (ERS and ERC are almost identical - one based on Sugar, the other on
Crystal, i.e. pure sucrose, recovery)
Ratooning ability

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Resistance to disease e.g. mosaic, smut, leaf scald

Resistance to Eldana borer
Proneness to lodging, i.e. falling over
Proneness to flowering

5.2.3. Crossing

As previously explained, in order to ensure pollen viability and to effect fertilization and
0
development of seed the developing flowers have to be kept in temperatures above 20 C.
Similarly, hybridization (crossing) has to be carried out in a heated glasshouse.

Many varieties that flower freely within the tropics flower seldom or not at all in KwaZuluNatal.
In the past this limited the number of possible combinations that could be made in breeding
work, but the use of the photoperiod house has addressed this problem. In this facility, flowers
are initiated in many varieties by imposing suitable daylengths.

When flowers are obtained, pollen fertility can be assured only by rearing the flowers in a
glasshouse, where they are provided with warm night temperatures. Stalks with flower initials
are marcotted (re-planted) after severing them from the stool. Vermiculite and compost is used
as a rooting medium which is enclosed in a metal sleeve. The severed canes are initially
placed in a nutrient solution until a new root system has been formed.

Separate crosses are made in individual compartments within the glasshouse. The so-called
‘male’ tassels are placed above the ‘females’, and shaken in the mornings to release their
pollen. When pollen shedding ceases, the males are discarded and the females moved to a
ripening area. When the topmost part of the tassels begins to fluff up and start to fall, the tassel
is harvested, dried, and the fuzz containing the seeds stored in a deep-freeze.

5.2.4 Seedlings

Seed sowing takes place annually in January. The fuzz is spread out on the surface of a
sterilized mixture of compost, soil and river sand and covered lightly with peat moss.
Germination can frequently be seen within two days. With certain crosses, only a few seedlings
are obtained, while with others, producing more viable seed thousands of seedlings can result.

The seedlings are moved outside the glasshouse for steadily lengthening periods until they
have hardened off. When they are about 3 to 5 cm tall, they are transplanted to pots. The
potted seedlings are kept trimmed until they are ready for planting out in the field.

5.2.5 Selection procedure

Varieties that have been developed in other countries and found to be of value there, are
introduced to South Africa as cuttings, and planted in the quarantine glasshouse at Mount

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Edgecombe. After quarantine, they are advanced directly to the observation plot stage at the
Pongola sub-station and follow the normal selection programme.

6. SOILS

Knowledge of soils is critical to long term success in cane growing because soils affect:

water holding / vehicle movement when wet

nematodes (need for nematocides)

nutrition

erosion / land preparation / minimum tillage

weed control

variety selection

irrigation system.

6.1 Nature and distribution of soils

Soils differ in depth, colour, texture and structure and they may contain distinct layers (called
horizons).

Some soil types in South Africa are:

coastal sands (mainly red and medium grained)

black heavy clays in bottom-land areas

shallow grey sandy loams

fertile dark alluvial soils (Northern areas)

porous red and yellow-brown clays (midlands).

In general the sugar industry soils can be classified into four categories, mainly according to
colour:

grey black red brown (humic).

6.2 Physical and chemical characteristics

6.2.1 Grey Soils

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Account for 60% of sugarbelt soils. Characterised by some severe limitations:

low water holding capacity

slow water intake rate
restricted internal drainage
high erodibility
poor aeration
prone to compaction, especially when wet
low reserves of nutrients
nematode hazard when clay is less than 8%.

6.2.2 Black Soils

Main limitations:

moisture stress due to low capillary conductivity

difficult workability
high shrink/swell movements
plastic when wet, cloddy when dry
poor drainage.

6.2.3 Red Soils

Make up 19% of cane soils.

Generally have good water intake rates and drainage but with reasonable water
retaining capacity. No major limitations.

6.2.4 Brown humic soils

Generally deep (>1 m). Have excellent physical properties with good intake rates and
drainage, good water holding capacity and low erosivity.

6.3 Some implications of soil characteristics

Surface water management

Soils with low water penetration rates and low water retention (eg grey soils) require
management to minimise run-off and conserve moisture. This involves:

careful field layout (strips)

correctly spaced and graded terraces

careful construction of waterways

land shaping to eliminate high spots and fill low spots.

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Sub-surface drainage - this is necessary to avoid waterlogging where drainage is poor.

Minimum Tillage (see later for details)

Particularly important with the erodible soils (greys) on sloping sites. Improved yields are
obtained.

Nematode control
Nematodes cause serious damage only in sandy soils containing less than 8% clay. Use of
nematocides generally increases yields in these soils.

Eldana control
Stressed cane is particularly prone to damage by Eldana. Eldana control by pre-trashing etc. is
therefore particularly important in soils which are prone to moisture stress.

Weed Control
Herbicide rather than mechanical weed control is important for erodible soils.

Harvesting
In soils which are prone to compaction it is important to avoid running heavy equipment in
fields that are wet. Harvesting programmes have to be adjusted accordingly.

Irrigation
Soil type influences:

frequency of cycles

types of irrigation system

application rates

acceptability of “salty” irrigation water.

Nutrient requirements
Black soils tend to have adequate phosphorous, brown organic soils mineralise large amounts
of nitrogen, red light soils require the most fertilizer and tend to lose it most easily through
leaching. Hence soil type influences the optimum quantity and balance of fertilizer required and
the frequency of application.

7. LAND PREPARATION

There are two main objectives:

1. to kill the old crop

2. to prepare a “seedbed”.

These are separate operation which take place several months apart.

7.1 Killing the old crop

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The reasons for doing this are:

to prevent transmission of disease from the old crop to the new

to ensure that any new variety planted is not contaminated with the variety being
replaced

to prevent volunteers from the old crop from growing between the new rows.

The methods used are:

mechanical

manual (by hand)

chemical.

7.1.1 Mechanical

The aim is to lift the old stools out of the ground, shake off the soil and leave the plant on the
soil surface to dry out. Deep ploughing tends to simply replant the stools and can result in a
delay of up to eight months in appearance of shoots from the buried stools. Deep ploughing is
a common fault made by commercial growers.

The first operation should be a shallow ploughing or harrowing to detach the plants from their
roots. This needs to be followed by a lifting operation to expose the stools. Suitable equipment
includes rotary hoes, springtine cultivators and subsoilers with wings.

Timing of mechanical eradication is important - fields to be replanted should be the first to be

harvested so that ploughing can start in May. Periodic harrowing should continue until late
August. Note that the land is fallow at the season of least growth and at the time when heavy
rainfall is least likely. Rain would help the stools to survive and could cause erosion of the
exposed soil.

If eradication has to take place in summer then chemical eradication should be used.
Mechanical eradication is relatively inexpensive if done properly.

7.1.2 Chemical

Two chemicals are available:

Monsanto’s “Roundup” and

ICI’s “Fusilade”.

Roundup leaves no active residues in the soil but Fusilade residues last up to two months.

Both chemicals are only effective when applied to actively growing cane and can therefore only
be used in summer. For spring application Fusilade is more effective than Roundup.

The crop must be harvested at least six weeks before the chemical is applied so that active
growth is underway at the time of application. The cane should be well tillered but without
stalks and complete spray coverage is necessary because the chemicals are not translocated
within the plant.

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Fusilade requires only an hour of contact time to be effective but roundup requires 6-8 hours
and should not therefore be applied if rain is anticipated. Spraying should not take place before
dew has dried.

Some cane varieties are less sensitive to these chemicals than others and need higher doses.

Chemical eradication is never 100% successful and should be followed with hand hoeing.

Manual hand hoeing is sometimes practised but is labour intensive - about 40 man-days per
ha.

7.2 Minimum tillage

Research has shown that yields are not depressed if land preparation is confined to narrow
strips into which the setts are planted - ie, if chemical eradication is used then the new crop
can be planted in a narrow strip of prepared soil in the interrow. This saves on land preparation
costs and on soil erosion, and often gives better yields (about 10%), particularly in light soils.

Minimum tillage is being strongly advocated in South Africa as the cheapest and most
environmentally friendly method. The chemical used to kill the cane (glyphosate) breaks down
rapidly in soil and does not pollute groundwater. The dead crop, together with the minimum
soil disturbance, helps to protect against erosion. On slopes exceeding 20% minimum tillage
is compulsory (ploughing illegal). Comparative costs in 2002 were:
Ploughing and harrowing 1360 R/ha
Chipping (hand hoeing) 1314
Minimum tillage 392
The major cause of failure of minimum tillage is improper application of spray. The crop must
have re-grown to knee height and be actively growing when sprayed. No rain must fall within
eight hours of spraying. The effectiveness can be improved by severing the cane stools from
their roots two weeks after spraying. This can be achieved with a stool plough or ripper fitted
with wings.

Good land preparation is very important - it affects germination of the new crop and
disease carry over to the crop. Poor germination leads to gaps and hence reduced
yields throughout the crop cycle. Disease carry over also affects the whole crop cycle.

8. PLANTING

This is another very important operation which affects productivity throughout the plant cycle.

8.1 The planting season

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This varies for different regions:

The semi-arid northern regions

Because of irrigation, moisture is generally not a limiting factor and temperatures are such that
planting can be done almost throughout the year with the exception of the two coldest months.
Ideally, planting should be complete by early summer to give the crop the benefit of a full
growing season.

The midland mistbelt region

Low soil temperatures preclude planting before September. This leaves only two months for
planting because if done later than October the plant crop does not canopy before winter and
this diminishes survival of the plants through winter. Also, if planting is delayed then the plants
are very young in summer and attractive to leaf hoppers which hatch in summer and spread
the mozaic virus.

The coastal lowlands

Planting can commence in August and continue to the end of October. Summer planting is
avoided due to erosion hazard and exposure to mozaic.

8.2 Planting methods

Heat-treated seedcane from disease-free nurseries is best. The setts are laid flat in furrows
and covered with soil to a depth of 30 to 50 mm. Uneven coverage results in uneven
germination. Excess depth causes delayed germination, which gives weeds a competitive
advantage.

Fertilizer is usually applied to the furrows before the setts but must be covered with soil to
prevent direct contact with the setts.

Most planting is done by hand but there are machines available for use on flat fields. The
machines create and cover the furrows in one pass. This prevents soil drying and ensures
even coverage of the setts.

Where soil desiccation is likely to be a problem it is helpful to add filtercake to the furrow at a
rate of 40 t/ha. A small amount of water (2,5 1/m) added to the furrow just before closing can
substantially improve germination in dry soil.

9. NUTRITION AND FERTILIZERS

The six most important elements for cane are N, P, K, Ca, Mg and S. For sustained growth it is

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usually necessary to add these to soils in the form of fertilizer. Most soils are capable of
supplying all the minor nutrients although there is evidence of Zn deficiency in some soils.

Nitrogen promotes green, vigorous growth but excessive amounts cause delayed maturity with
reduced juice purity and high juice colour.

Phosphorous is necessary for good root growth and crop maturation. Deficiency causes
stunted growth and leaf blades are slender, often bronzed and die back from the tips.

Potassium ensures long cell life with good chlorophyll development. It has a role in the control
of stomatal opening and closing and it therefore affects the drought resistance of the crop.
Deficiency results in depressed growth, with yellow/brown discolouration of lower leaves and
scorching of outer edges. The leaf blade midrib is often discoloured (red).

Calcium deficiency causes reduced top and root growth but specific symptoms are not
obvious. Large excesses of Ca induce chlorosis due to iron deficiency.

Magnesium is a component of chlorophyll. Deficiency causes red freckling particularly on older

leaves.

Sulphur deficiency causes light green leaf blades which do not die back from their tips as when
N is deficient.

9.1 Inorganic Fertilizers

9.1.1 Nitrogen carriers

Urea is the most commonly used because it is relatively cheap and has a high N content (46%)
and so is relatively cheap to transport and apply. It is sold as white granules which are very
hygroscopic.

Ammonium sulphate (21% N. 24% S) Causes acidification of soils and so is used mainly on
alkaline soils. Such soils may also benefit from the S.

Anhydrous ammonia (82% N) was used in Swaziland but has been discontinued. It is supplied
in pressurised cylinders and needs special equipment for application - it has to be injected
below the soil surface.

9.1.2 Phosphate

Single supers (10,5% P: 10,2% S: 20% Ca) is manufactured from rock phosphate by treatment
with sulphuric acid. Phosphate is not very mobile in soil and so the fertilizer needs to be applied
to the furrow prior to planting.

9.1.3 Potassium

Potassium chloride is the only commonly used source of K used in SA. It has to be imported
and about 200 million rands worth are used by the sugar industry each year. Much of it ends up

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in molasses so there is good sense in trying to recover it.

Application of individual nutrients

P is best applied to the furrow but because N and K are easily leached, not all is applied to the furrow -
some is applied to the soil surface as a top dressing when growth is well under way. In the case of
ratoon all the fertilizer has to be applied as a top dressing and it is important to do this before much
regrowth has occurred.

9.1.4 Mixtures

The various nutrients are made available as mixtures containing various proportions. These
mixtures may be bulk blends consisting simply of the various nutrient carriers mixed together.
There is a tendency for separation to take place because particle sizes of the various carriers
are different. To overcome this problem the mixtures may be ground to a fine powder and then
granulated. They are then called compounds.

The composition of mixtures is indicated by a convention which expresses the proportions of

N:P:K in that order followed by a bracketed figure which indicates the percentage which N,P
and K together make up - eg, 5:1:5(42) shows that 42% of the mixture consists of N,P and K
and that these are in the proportions 5(N):1(P):5(K). Hence the N content is 5/11ths of 42%.

9.2 Organic Manures

Filter cake is the most commonly used organic manure. Details are give in the following
SASRI information sheet.

SASRI INFORMATION SHEET : FILTERCAKE USE

General
Filtercake used to be available in large quantities (800,000 tons per annum), but was used only to a
limited extent because of its bulk and relatively high cost of application. Its use also slows down the
planting operation. The nutrient balance is hardly ever ideally suited to sugarcane and consequently
balancing with inorganic fertilizers is usually necessary.

Moisture content: The moisture content of fresh filtercake is approximately 70%, which makes it
expensive to transport. It dries out when left in the field to about 60% moisture.

Nutrient content (on a dry matter basis):

Nitrogen : 1,6% (Approximately 50% is available to the crop when applied to midlands soils,
which have a high organic matter content, but only approximately 20% is available when it is
applied to other soils).

Phosphorus : 1%

Potassium : 0,2%

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On average, filtercake is equivalent to a 3:5:1 fertilizer, and is therefore primarily a planting mixture. A
ton of filtercake with a 70% moisture content has a nutritional value which is usually below the cost of
transport to the farm.

Application rates : In general, 30 tons of the fresh material (70% water) per hectare in the planting
furrow will provide adequate phosphorus and nitrogen for midland soils , which have a high capacity to
mineralise N. To balance nutrient requirement only potassium chloride would be required. In other
areas on many soils the above application rate would be less appropriate.

Example: (Other areas : 20% N available)

Standard FAS recomuendations (kg/ha)
N : 120, P : 30, K : 125
30 tons/ha filtercake at 70% moisture will provide

N : 30 kg/ha, P : 90 kg/ha, K : 18 kg/ha

P. is now supplied in excess. To balance the nutrient requirements the following additional amounts of
fertilizer would be required as a top dressing

90 kg N from 200 kg/ha urea

100 kg K from 200 kg/ha potassium chloride
or 400 kg/ha 1:0:1 (47)

If filtercake is broadcast and incorporated before planting then about twice the in-furrow rate will be
required.

Recommendations for the use of filtercake at planting for

different soil groups

Priority Soil Soil form

rating description or area Reasons

Inanda The best responses are obtained

Kranskop because the high P content largely
Clovelly overcomes the P fixing capacity of the
1 High P-fixing soils Hutton soil

Midlands The value of filtercake here is again its

Soils with a low P and virgin high P content and it should be used at
2 status soils 30 - 40 t/ha applied in the furrow

The high moisture content (about 70%)

All soils for winter and early spring protects the seed cane from desiccation
3 planting if planting rains are late

Bonheim Filtercake envelops the cane setts and

Heavy clay soils Rensburg reduces air pockets in the coarse
4 with coarse tilth Milkwood seedbed

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Other characteristics of filtercake

Effect on sucrose % cane

Sucrose % cane may be lowered quite substantially by the application of this material, even
when the N content of filtercake is taken into account. This is because the N is released
gradually and thus can delay ripening of the cane. When using filtercake the rate of applied N
fertilizer must be reduced, particularly in midlands mistbelt soils.

Nematlcidal effect
This effect is short-lived and of limited value. Filtercake is not an alternative for a nematicide.

Residual effects of filtercake

Only in the midlands mistbelt soils has a substantial residual response been measured in the
first ratoon crop to filtercake applied at planting.

Fly ash
At some mills fly ash may be incorporated into filtercake which reduces the N and P contents
and therefore its nutrient value.

Ratoon chlorosis
To reduce the risk of ratoon chlorosis in cane growing on neutral to alkaline soils do not apply
high pH filtercake produced by factories where refinery filtercake (CaCO3)is mixed with mill
filtercake, ie. Pongola and Gledhow.

Note Because of the variable nutrient content of filtercake it is recommended that representative
samples are submitted in sealed containers to the Fertilizer Advisory Service for analysis in
order to obtain advice on optimum application rates.

In the late 1990s there was a steady trend towards recycling filter mud to diffusers thereby reducing
availability of filtercake. Smuts, from flue gas scrubbers, is still produced but has a low nutrient
content. Smuts and boiler ash have value as a source of soluble silica, which has been shown to
increase cane growth on some soils and to increase resistance to Eldana.

9.3 Fertilizer Advisory Service (FAS)

Soil samples can be submitted to SASRI for analysis and advice on fertilizer requirements. The
advice usually covers the plant crop as well as two subsequent ratoons. It is based on the
results of the soil analysis as well as knowledge of the soil type and the anticipated yield of the
crop (irrigated or not).

10. HARVESTING

Harvesting is confined to about 38 weeks of the cooler months (April to December) because:

rainfall is mainly in the summer months and it interferes with harvesting

weather conditions in January - March are not conducive to the strenuous exercise of manual

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harvesting

the crop grows most vigorously during the summer months but if it is harvested during these
months it has little leaf material to take advantage of the good growing conditions

the sucrose content is at its lowest when the cane is growing vigorously, i.e. in summer.

The harvesting process is the subject of a separate module and will not be repeated here except to
add that there is increasing evidence that trashing, rather than burning, might be the best choice in
many situations. The major reason for a changing attitude is the realisation that cane deterioration has
a much greater adverse effect on sugar yields than does the inclusion of trash (removed by burning).
A major cause of deterioration is the delay between burning and cutting, brought about by the need to
burn large areas at a time. In addition, burnt cane deteriorates more rapidly than unburnt cane. The
introduction of the RV system for cane payment means that the accumulation of deterioration products
(non-pol) is penalised, in addition to the penalty of lower sucrose content.

10.1 Comparison of trashing with burning

Advantages of a trash blanket:

· Improved yields, especially in dry years (average overall increase is 9% but variable)
· Improved water conservation (by 90% on an 11% slope) and soil conservation (by 60% on the
11% slope)
· Suppression of weed growth (about 45% saving in cost of weed control)
· Prevention of soil capping and reduction in evaporation
· Eliminates problems of smoke pollution associated with burning
· Reduces the amount of P fertilizer likely to be fixed in acid soils
· Decreases the likelihood of soil compaction.

All of these contribute to higher yields on the coastal lowlands.

Disadvantages of a trash blanket:

· A lower harvesting rate by the cane cutters (up to 45% greater cost of harvesting)
· Poorer payloads (up to 33% less) if trashing is not done well
· Increased extraneous matter into mill. A 1% increase in extraneous matter will:

decrease extraction by 0,4%

reduce purity by 0,3%

increase clear juice colour by 3,6%

increase clear juice turbidity by 4,2%

reduce crushing rate by 2 - 3%
· Delayed ratoon regeneration in winter - serious on cold South-facing slopes
· Loss of cane under the trash blanket unless gleaning is effective

When Eldana infestation is heavy it is essential to burn rather than trash.

When burning takes place there is benefit in leaving the burnt tops scattered over the soil.
Experiments conducted during different seasons on a range of different soil types produced the
following average response in tons cane per hectare per year due to leaving the full trash or the burnt

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tops scattered (instead of raking and re-burning them).

Crop High potential soils Moderate to low potential soils )

Trash Burnt tops Advantages Trash Burnt tops Advantage

blanket scattered to trash blanket scattered s to trash

Starting in
summer 10 6 4 6 5 1

Starting in
winter 4 3 1 nil nil -

Ground cover provided by the scattered tops varies widely from about 100% from a cool burn of a well-
grown crop to as little as 10% from a hot burn of a droughted crop. As inadequate soil protection
occurs in the latter case on steep slopes and erodible soils, burning is not recommended.

The importance of trash for weed control

A well-spread trash blanket controls weeds well and can reduce herbicide expenses significantly.
Where burnt tops are left scattered, herbicides are essential. Both pre- and post-emergence
herbicides are effective when applied over scattered tops, but they must be applied at the right time.

10.2 Codes of burning practice

In 1995 the industry adopted a set of codes which growers are expected to abide by. In some mill-
group areas, non-conformance can result in the offending grower being barred from delivering cane
for a defined period.

The codes aim to reduce the nuisance of smoke and smuts in residential areas and roads. They
require farmers to not burn near sensitive areas and to take note of weather forecasts before burning
(some groups of farmers have daily wind predictions sent to them by SMS). Burning at weekends is
not allowed.

11. CANE GROWTH ON STREAM BANKS AND WETLANDS

There has been considerable debate and argument over the distance growers need to pull back from
streams and rivers. The Act states this distance should be 10 metres from the 1 in 10 year flood line
on all streams and rivers. This distance is acceptable when applied to large rivers and farm streams,
but was found to be unnecessarily wide and impractical for the many watercourses on farms with small
catchments. In response to the need for guidelines in these situations, SASRI has developed rec-
ommendations that can be used to ensure that these smaller watercourses are adequately protected.

The destruction of wetlands by draining them and planting cane has been recognised as a bad
practice and is being reversed.

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12. COSTS OF PRODUCTION

The various costs of cane production are approximately as follows (% of total cost):

2007/8 2009/10
Staff 26% 22%
Contractors 8 6
Chemicals 5 4
Fertilizer 14 23
Fuel & lubricants 7 9
Maintenance - mechanical 7 7
- fixtures 5 4
Insurance & licences 9 8
Sundry 5 5
Cane transport 14 11

In 2009/10 the average price paid for cane was R284 /t.

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