a study of soil loss and sugar cv. naidiri) on a sloping...

A STUDY OF SOIL LOSS AND SUGAR

CONTENT IN SUGARCANE (SACCHARUM

OFFICINARUM CV. NAIDIRI) ON A

SLOPING FARM IN FIJI

A thesis presented in partial fulfillment of the

requirements for the degree of Master of Science at the

University of the South Pacific

ASHWEEN NISCHAL RAM

2006

ii

DECLARATION

I declare that this thesis is a report of research work

carried out by me and has not been submitted in any form for

another degree or diploma at any university. Information

obtained from published or unpublished work of others and

help received in setting up of field studies have been

acknowledged.

Candidate: ASHWEEN N RAM

Supervisors:

Dr. Angeela Jokhan

Associate Dean

Faculty of Science and Technology

University of the South Pacific

Jai Shree Gawander

Research Manager

Sugarcane Research Centre, Fiji Sugar

Corporation Limited

iii

ABSTRACT

The growing of sugarcane on sloping land receiving high

intensity rainfall causes extensive soil erosion in Fiji.

This soil loss and accompanying declining cane yields on

undulating terrain are of major concern to the Fijian sugar

industry. In recent years the growers have not only

abandoned best management practices to conserve soil but

they have also uprooted the border crop vetiver grass that

was planted at the time of expansion of the cane belt. This

to a large extent has accelerated the loss of top soil and

thus soil degradation causing, with the burning of trash,

the yield to decline even more rapidly.

As quantitative data on erosion from field plots are scanty

in Fiji, an experiment was initiated on a sloping cane farm

(8o slope) to determine soil loss under different management

practices and impact on the cane yield of the plant cane and

of ratoon crops.

Significant (P<0.05) responses in cane and sugar yields of

the plant cane crop were found but this was probably due to

the increased length of planting within a treatment-plot

rather than best management practices used. In ratoons, no

significant response to the best management practices

adopted was found. However, in plots in which trash was

iv

conserved and cane planted across the slope produced higher

(>80 tcha-1) cane yield compared to other three treatments

with no trash (T 1-cane planted across slope, T 2-cane

planted uphill and downhill, T 3-cane planted across slope

with vetiver hedgerow).

The retention of trash and cane planted across the slope

would earn the grower an additional F$150-$400 and F$700-

$1000 in the first and second ratoon crop respectively.

Soil loss was largely affected by the different planting

strategies associated with the conservation practices.

Trash acted as buffer under high intensity rain with the

result that only 153 and 221 kg soil ha-1yr-1 were eroded in

the first and second ratoon crops, respectively. Where the

sugar cane was planted uphill and downhill soil losses were

16 376, 259 and 2274 kgha-1yr-1, in plant cane and in the two

succeeding ratoon crops, respectively. The very low soil

loss in the first ratoon crop could be attributed to the

drought conditions prevailing that year. The annual

rainfall for study period (2001-2004) was 2140, 1007 and

2351 mm for plant cane crop and ratoon crops being 92, 43

and 102 % of the 117 years long-term mean.

The top soil properties including pH, organic matter (OM),

available P and exchangeable bases monitored after harvest

of successive crops indicated that changes could generally

v

be related to a change in organic matter (decrease) and

associated ion exchange properties with increasing period of

cultivation. Treatments 1, 2 and 3 were affected more than

the trash retained plot. Such was the case that organic

matter decreased by 33 % where cane was planted uphill and

downhill from the time of initial sampling to final harvest.

As observed during the study trash mulch reduced weed

infestation, increased water retention in the root zone for

healthy plant growth and provided better anchorage in

regards to cane lodging compared to other plots. In view of

the above, growers will realize the benefit in terms of zero

tillage, spot spraying compared to broad application of

herbicides, harvesting of green cane, improved soil

fertility and sustained production level.

Planting sugar cane across slope and conserving trash mulch

therefore reduces soil erosion and with increasing period of

cultivation will sustain cane production to provide stable

economic return to the farmers. This practice is

environmentally friendly and cost effective.

vi

ACKNOWLEDGEMENTS

I wish to express my sincere thanks to Research Manager (Mr.

Jai S Gawander) for his support, motivation and guidance

during the study period. I am thankful to Messrs Karuna

Garan and Maciu Talebulamaimaleya for maintaining and caring

of the trial at Navoli. The contribution of the support

staff of the Crop Management section at the Sugarcane

Research Centre and those at Rarawai is also acknowledged.

I acknowledge the continued guidance by my supervisor Dr

Angela D Jokhan of The University of South Pacific in the

preparation of the thesis. A special note of appreciation

to Professor John Morrison of University of Wollongong, NSW

for his advice during the studies.

My sincere thanks to Fiji Sugar Corporation Limited for

financial support and time is gratefully acknowledged. Mr

Jeeteendra Patel, Abdul Kadir, Shiva Padayachi, Nemani Soli,

Pedro Rounds and Desmond Kumar are also thanked for their

assistance.

Vinaka

vii

TABLE OF CONTENTS

Page

DECLARATION............................................. ii

ABSTRACT................................................ iii

ACKNOWLEDGEMENTS........................................ vi

TABLE OF CONTENTS....................................... vii

LIST OF FIGURES ....................................... xi

LIST OF TABLES.......................................... xv

CHAPTER 1

INTRODUCTION............................................ 1

CHAPTER 2

LITERATURE REVIEW....................................... 9

2.1 Soil erosion.................................. 9

2.1.1 Geologic and accelerated erosion.... 9

2.1.2 Water erosion....................... 10

2.2 Role of vegetation on soil erosion........... 13

2.3 Soil erosion in Fiji.......................... 15

viii

CHAPTER 3

MATERIALS AND METHODS................................... 23

3.1 Trial site.................................... 23

3.2 Soil sampling................................. 24

3.2.1 Soil preparation.................... 24

3.2.2 pH (H2O)............................. 24

3.2.3 Exchangeable Ca, K and Mg........... 25

3.2.4 Soil phosphorus (modified Troug) ... 25

3.2.5 Organic matter...................... 26

3.2.6 Soil texture........................ 27

3.3 Trial design.................................. 27

3.4 Plot layout................................... 29

3.5 Runoff tipping bucket......................... 31

3.6 Monitoring of soil loss and runoff............ 36

3.6.1 Bed load.............................. 36

3.6.2 Runoff................................ 37

3.7 Climatic data................................. 37

3.8 Planting...................................... 37

3.9 Treatments.................................... 38

3.10 Fertilizer application........................ 39

3.11 Weed control.................................. 40

3.12 Crop growth measurement ...................... 40

3.13 Harvesting.................................... 41

3.14 Cane juice analysis........................... 41

3.15 Statistical analysis.......................... 42

ix

CHAPTER 4

RESULTS................................................. 43

4.1 Soil type and analysis........................ 43

4.2 Plant crop ................................... 51

4.2.1 Germination......................... 51

4.2.2 Tillers per stool................... 53

4.2.3 Stalk length........................ 53

4.2.4 Stalk population.................... 55

4.2.5 Cane and sucrose yield.............. 58

4.2.6 Runoff and soil loss................ 64

4.3 First ratoon crop ............................ 71

4.3.1 Cane and sucrose yield ............. 71

4.3.2 Runoff and soil loss................ 74

4.4 Second ratoon crop............................ 80

4.4.1 Growth measurement parameters....... 80

4.4.2 Cane and sucrose yield.............. 83

4.4.3 Soil loss........................... 86

CHAPTER 5

DISCUSSION.............................................. 76

5.1 Top soil samples.............................. 92

5.1.1 Soil pH............................. 92

5.1.2 Organic matter...................... 93

5.1.3 Available P......................... 93

5.1.4 Exchangeable K...................... 94

5.1.5 Exchangeable Ca + Mg................ 94

5.2 Climatic conditions........................... 95

x

5.3 Crop cycle.................................... 96

5.4 Treatments – Planting strategy associated with

conservation practice ........................ 97

5.5 Crop growth parameters ...................... 98

5.5.1 Germination ....................... 98

5.5.2 Tillers............................. 99

5.5.3 Stalk population.................... 99

5.5.4 Stalk length........................ 100

5.6 Cane and sucrose yield........................ 100

5.7 Runoff and Soil loss.......................... 102

5.8 Current soil conservation constraints and

Implications.................................. 106

5.8.1 Land tenure legislation............. 106

5.8.2 Extension service................... 107

5.8.3 Economic implications of erosion.... 108

CHAPTER 6

CONCLUSION and RECOMMENDATIONS.......................... 110

REFERENCES.............................................. 115

APPENDICES.............................................. 125

xi

LIST OF FIGURES

Figure Page

1.1 (a) Vetiver grass in nature; (b) Vetiver

grass filtering water & soil particles coming

down the slope.................................... 5

1.2 New promising variety LF82-2122.................... 7

1.3 Exposed stalk, turns reddish brown............... 7

3.1 The trial design for the experiment at Navoli,

Veisaru, Ba was a 4 x 4 randomised complete block

design with four treatments replicated four times

randomly. The slope direction is indicated by

arrows marked on the plots ....................... 28

3.2 The author with Rarawai employees during initial

stages of trial work at Navoli, Veisaru, Ba. As

indicated by arrows the layout of the trial shows

different planting strategy used in the study...... 30

3.3 Experimental plot showing the arrangement of tipping

bucket, collection trough and manifold at Navoli,

Veisaru, Ba on a sloping cane farm................ 32

xii

3.4 Plan view of runoff collection trough.............. 33

3.5 Cross section of the layout........................ 34

3.6 Cross section of collection trough, manifold and end

plate.............................................. 35

4.1 Variation in the pH with time (P-plant crop, R-first

ratoon, S-second ratoon) after initial land

preparation. The means are average of four

replicates. Details on the respective treatments

are presented in Table 3.1..................... 44

4.2 Variation in the OM with time (P-plant crop, R-first




are presented in Table 3.1....................... 45

4.3 Variation in the P with time (P-plant crop, R-first





xiii

4.4 Variation in the K with time (P-plant crop, R-first





4.5 Variation in the Ca with time (P-plant crop, R-first





4.6 Variation in the Mg with time (P-plant crop, R-first





4.7 Histogram showing the means of tonnes cane per

Hectare (tcha-1) for each of the four treatments

in plant crop. The means are average of

four replicates.................................... 62

4.8 Histogram showing the means of tonnes sugar per

Hectare (tsha-1) for each of the four treatments

in plant crop. The means are average of

four replicates.................................... 63

xiv

4.9 Surface runoff affected by different planting

strategies associated with conservation practice

in plant crop at Navoli, Veisaru, Ba on a sloping

cane farm. The means are of four replicates....... 67

4.10 Soil erosion affected by different planting

Strategies associated with conservation practice

in plant crop at Navoli, Veisaru, Ba on a sloping

cane farm. The means are of four replicates ...... 68

4.11 Surface runoff affected by different planting

strategies associated with conservation practice in

first ratoon at Navoli, Veisaru, Ba on a sloping cane

farm. The means are of four replicates............ 76


Strategies associated with conservation practice in

first ratoon at Navoli, Veisaru, Ba on a sloping

cane farm. The means are of four replicates....... 77


Strategies associated with conservation practice at

Navoli, Veisaru, Ba on a sloping cane farm. The

means are of four replicates...................... 89

5.1 Effects of soil erosion .......................... 105

xv

LIST OF TABLES

Table Page

2.1 Indicating the land use, slope and soil loss from

six plots studied (from Leidtke, 1984)............ 17

3.1 Summary for plant and ratoon crop Treatments used

in plant and ratoon crop at Navoli, Veisaru, Ba on

a sloping cane farm. In plant crop T #1 and 4 were

identical but in ratoon T #4 had trash retained

compared to other three treatments which had no

trash 35......................................... 39

4.1 Chemical characteristics (initial) of Navoli soil

collected from a depth of 0-200 mm. Soil analyses

included pH, organic matter content, available

phosphorus, exchangeable bases and cation exchange

capacity (CEC).................................... 50

4.2 Physical Characteristics of Navoli soil collected

from a depth of 0-200 mm. Characteristics included

% sand, silt, clay and textural class............. 50

4.3 Germination count taken 6-8 weeks after planting

in each plot at Navoli, Veisaru, Ba. Details on

the respective treatments are presented in

Table 3.1......................................... 52

xvi

4.4 Growth measurements taken at 4, 5, 6 and 7 months

included tiller and population count, and stalk

height measurement. Details on the respective

treatments are presented in Table 3.1............. 57

4.5 Effect of different planting strategies associated

with conservation practice in plant crop at

Navoli, Veisaru, Ba on a Sandy clay loam soil. The

means are average of four replicates ............. 60

4.6 Tukey’s all-pairwise comparison test of cane and

Sugar yield in plant crop. Means followed by a

common letter are not significantly different at

5% level of significance......................... 61

4.7 Rainfall and average temperature summary for plant

crop at Navoli, Veisaru, Ba...................... 69

4.8 Summary of surface runoff and soil loss affected by

different planting strategies associated with

conservation practice in plant crop at Navoli,

Veisaru, Ba on a sloping cane farm................ 70


with conservation practice in first ratoon crop

at Navoli, Veisaru, Ba on a Sandy clay loam soil.

The means are average of four replicates.......... 73

xvii

4.10 Rainfall summary for first ratoon crop at Navoli,

Veisaru, Ba....................................... 78

4.11 Summary of surface runoff and soil loss affected by

different planting strategies associated with

conservation practice at Navoli, Veisaru, Ba on a

sloping cane farm................................. 79

4.12 Growth measurements taken at 3, 5, 7 and 9 months

included tiller and population count, and stalk

height measurement. Details on the respective

treatments are presented in Table 3.1........... 82


with conservation practice in second ratoon crop at

Navoli, Veisaru, Ba on a Sandy clay loam soil.

The means are average of four replicates ......... 85

4.14 Rainfall summary for second ratoon crop at Navoli,

Veisaru, Ba ................................... 90

4.18 Summary of soil loss affected by different planting

strategies associated with conservation practice at

Navoli, Veisaru, Ba on a sloping cane farm........ 91

1

Chapter 1

INTRODUCTION

The sweet sugarcane is a member of the family Gramineae of

the genus Saccharum that is placed in the tribe

Andropogoneae. The Andropogoneae are characteristically

tropical and thrive in the tropics of the Pacific and the

Indian subcontinent. Varieties of sweet cane (Saccharum

officinarum) have been found growing naturally in Indonesia,

the Philippines, Fiji and Papua New Guinea (Deerr, 1911;

Potts, 1955). The proposed centres of origin for sweet

sugarcane may have been in India but disappeared from the

subcontinent and now thrive in the rainforest of Papua New

Guinea, Hawaii and Fiji (Panje, 1971; Sreenivasan, 1987).

Today, sugarcane is a major agricultural crop in some sixty

subtropical and tropical countries with a total production

of approximately 139 million tonnes of centrifugal sugar

(Current World Production, Market and Trade Report, 2003).

In 1975, world sugar demand was approximately 75 million

tonnes and since then it has risen by 50% to almost 114

million tonnes in 1994, a growth rate of 2.1% sugar per year

(Fry, 1997). In these countries, sugarcane produced is

three times larger than the rice paddy crop and five times

larger than wheat or corn crops. In these countries, some

2

seven to eight million people are employed in the sugar

industry and thirty million or more are directly dependent

on sugar industry income (Gawander, 1997).

The only sugarcane available had originally been obtained

from native gardens. These plants had thick, brightly

coloured stalks that contained sweet juice. They were low

in fibre and easy to chew and crush in the mills. The

sugarcane scientists of the day were much impressed with

their handsome appearance that they called them the “noble”

space canes. The first step Colonial Sugar Refinery (CSR)

took in improving production was to import the best

varieties (germplasm) from overseas and then select the best

for the Fijian conditions. By 1903, a breeding station was

established at Rarawai, Fiji. This was the third station to

be established in the world, preceding the better known

stations such as Coimbatore, India, and Canal Point,

Florida, which were not established until 1910 (Gawander,

1997).

Sugarcane has been responsible for shaping the history of

Fiji. It led to the establishment of commercial cane farms

and the arrival of indentured labourers from India to work

on the plantations. After World War II, the demand for

sugar increased and large areas in the Western Viti Levu

were brought under cane mostly on undulating terrain with

poor soils (Valaibula, 1984). With independence, the need

3

for sugar dollars was even more demanding and despite the

various expansions there was a period of decline in yield

from about 1970 to 1975 (Valaibula, 1984). The attractive

prices during the mid-seventies and the desire to increase

production of sugar resulted in the expansion of the sugar

industry to less fertile and strongly weathered soils.

These soils were generally low in major nutrients such as

nitrogen, phosphorus and potassium and many also have high

levels of aluminum and manganese (Gawander and Naidu, 1989).

Soil erosion is major problem in the cane belts in Fiji as

shown in Appendix 5. Approximately 70 % of the total 93,000

ha of land available for cane planting is located on hilly

lands (FSC, 2002). Annual rainfall in the cane belt ranges

from 1800 to 2600 mm. High intensity precipitation during

the wet season accounts for 60 % of the annual rainfall.

The main soil types on the hilly land are ferruginous

latosol, humic latosol and nigrescent soils with moderate to

high erodibility (FSC, 1995). High rainfall intensity,

steep slopes and over cultivation have resulted in serious

soil erosion.

Most cane farmers are reluctant to take effective soil

conservation measures or simply ignore the danger of soil

degradation. Poor management by farmers not only aggravates

the soil erosion problem but also reduces soil productivity.

4

Vetiver grass was introduced to Fiji from India, most

probably for the purpose of thatching material for houses.

It was commonly used to stabilize embankments, terraces and

to demarcate farm boundaries. The use of vetiver in the mid

1950s to reduce soil erosion on steep slopes on which cane

was planted, indicated the potential of using vetiver as a

conservation measure. Recognising the many advantages of

the vetiver hedge it was recommended for planting in contour

lines instead of graded banks and waterways. They suited

the sugarcane farming system because it was more labour

intensive than mechanical. This soil conservation

technology was vigorously enforced over half of the sloping

lands. An internal report (224N) records approximately 20 %

loss of top soil due to the torrential rain on 9 April 1958.

The situation was described as catastrophic in the Wairuku,

Penang area. It further stated that considerable contouring

with vetiver hedge was hardly effective in controlling

erosion. The poor control was attributed to the fact that

the hedge was only recently established. The report

mentions loss of faith by some growers in the erosion

control measure. However, there were many who had well

established hedges and they remained convinced of its

effectiveness.

In-spite of the clearly demonstrated usefulness of vetiver

hedges in existence for sixty years it is amazing that

growers are very reluctant to establish new vetiver hedges.

5

In many cases the well established hedges have been removed

resulting in massive soil erosion and reduction in cane

yields.

Figure 1.1: (a) Vetiver grass in nature; (b) Vetiver grass

filtering water & soil particles coming down

the slope. Source: The Vetiver Network Website,

www.vetiver.org

(a)

(b)

6

Planting of vetiver grass is encouraged on sloping farms.

The vetiver grass quickly forms a narrow, dense hedge. Its

stiff foliage blocks the passage of soil and debris. It

also slows any runoff and gives rainfall a better chance of

soaking into the soil. However, farmers have ignored this

vetiver-technology although it is easy to establish and does

not require any major capital investment.

Despite the various expansions of the sugarcane growing

areas, the Fiji sugar industry has consistently had

difficulty in achieving the target figure of 500,000 tonnes

of sugar annually. This is not surprising, as although

better sugarcane varieties have been produced through plant

breeding research, very little effort has been directed

towards soil conservation. In actual fact there have been

no soil erosion studies done on sugarcane in Fiji and thus

there is no information available in relation to soil loss

and plant growth.

This research was carried out on the Naidiri (LF82-2122)

cultivar as illustrated in Figures 1.2 and 1.3. It was

introduced for commercial cultivation in 2000. Naidiri has

a better maturing characteristic of the male (MQ33-371)

parent and acquired its fast, vigorous growth

characteristics from the female (LF60-3917) parent.

Research data has shown that Naidiri is not only the

earliest maturing variety but it retains its high level of

(a)

(c)

7

sucrose through most part of the crushing season (Ram et al.

2003). Its high sucrose yield and other characteristics are

thought to improve the sugar production and bring additional

money to the ailing sugar industry.

Figure 1.2: New promising variety LF82-2122 (Naidiri).

Figure 1.3: Exposed stalk, turns reddish brown.

8

The objectives of the present study are to:

1. Assess the impact of different planting strategies

associated with conservation practice on plant growth and

yield parameters.

2. Assess the impact of different planting strategies

associated with conservation practice on surface runoff

and soil loss.

This study focused on:

Crop growth parameters,

Cane and sugar yield,

Cane juice analysis (pol, brix, fibre and %Pure

Obtainable Cane Sugar) and

Surface runoff and soil loss.

9

Chapter 2

LITERATURE REVIEW

2.1 Soil erosion

2.1.1 Geologic and accelerated erosion

There are two major rates of erosion i.e. geologic and

accelerated. Geologic erosion is a normal process,

representing erosion of land in its natural environment

without the influence of man. It is caused mainly by the

action of water, wind, variations in temperature, gravity

and glaciers. Accelerated erosion is in excess of geologic

erosion and is induced by human activities, which bring

about changes in natural cover and soil conditions.

Accelerated erosion results from human activities when

preparing land for crop production and as a place to build

homes, industrial plants, transport facilities and roads

(Zonn, 1986; Morgan, 1995).

According to Morgan (1995) the effects of soil erosion are

found both on- and off-site. On-site effects are

particularly important on arable land where various forces

are active such as redistribution of soil within a field,

loss of soil from the field, breakdown of soil structure,

10

decline in organic matter and reduction in nutrients

compounded by reduction of soil depth for cultivation.

Soil erosion, whatever the cause may be, gradually makes

land uninhabitable. As soil becomes depleted due to erosion

by water, people attempt to move to other more productive

areas. Eventually, when there is no more land available,

the farmers are forced to adapt themselves to lower yield of

crops. Barren lands require intensive cultivation and

extensive nutrient application to produce crops. It is

therefore essential that countries suffering from erosion

should adopt an enlightened land-use policy and provide

means to carrying out innovative soil conservation methods.

2.1.2 Water erosion

The soil lost through water erosion is usually the most

fertile component which contains the plant nutrients,

organic matter and fertilizers. What is usually left is the

least productive component, which is generally barren and

unproductive.

The impact of raindrops on the bare soil surface, and the

flow of run-off causes detachment of soil particles and

transport down slope and downstream. Without a protective

covering of vegetation, the impact of raindrops breaks down

the surface soil structure, sealing it off to water

11

penetration. This causes puddling of the surface, and small

soil particles go into suspension (Wallens, 1981).

Raindrops striking this surface splash fine soil particles

into motion. The infiltration rate into the soil has been

slowed down, so water accumulates and begins to run off.

This carries the fine particles off with it.

If intense rain is received more water runs off, it

concentrates in depressions and small flow lines and begins

to cut channels in the soil that may result in sheet and

rill erosion. The former is removal by runoff water of a

fairly uniform, usually imperceptible, thin layer of soil

often accompanied by formation of many small eroding

channels. Rills are only a few inches deep and do not

hinder farm machinery. Tillage erases them, but they tend

to recur after heavy rain during the growing season,

especially where canopy cover is limited (Natural Resources

Inventory, 1997)

Erosion also reduces available soil moisture, resulting in

severe drought-prone conditions. The net effect is loss of

productivity which, at first, restricts what can be grown

resulting in increased expenditure on fertilizers to

maintain yields, but later threatens crop production and

leads ultimately to land abandonment. It also leads to a

12

decline in the value of the land as it changes from

productive farmland to wasteland.

Off-site problems resulting from downstream sedimentation,

which reduces the capacity of rivers and drainage ditches,

enhances the risk of flooding, blocks irrigation canals and

shortens the design life of reservoirs. Many hydro-

electricity and irrigation projects have been ruined as a

consequence of erosion. Sediment is also a pollutant in its

own right and through the chemicals absorbed which can

increase the levels of nitrogen and phosphorus in water

bodies resulting in eutrophication (Pimentel, 1993).

Vogel (1990) stated that all types of water erosion are now

visible, following the collapse of terrace walls, erosion is

reducing the depth of the already shallow soil by one to

three centimeters per year.

Roose (1967) studied experimental data in Senegal and showed

that 68 % of the erosion on hillsides between the years 1959

and 1963 took place in rainstorms of 15 to 60 mm. of

precipitation. These storms have a frequency of about ten

times per year. Studies of erosion in mid-Bedford-shire,

England (Morgan et al. 1986) indicate that in the period

1973 to 1979, 80 % of the erosion occurred in thirteen

storms, the greatest soil loss i.e. 21 % of the erosion, was

caused by a storm with 57.2 mm of precipitation. These

13

storms have a frequency of between two to seven in a year

(Lal, 1976). In Zimbabwe 50 % of the annual soil loss

occurred in two storms in one year with 75 % of the erosion

taking place in ten minutes (Hudson, 1981).

2.2 The role of vegetation on soil erosion

The factors that influence the rate of erosion are rainfall,

wind, soil structure, slope, plant cover and the presence or

absence of conservation measures. Protection measure

includes plant cover to intercept rainwater in reducing the

velocity of the runoff and thus protecting the soil from

erosion. Clearance of the vegetation leads to an increase

in the velocity of the runoff resulting in rapid erosion as

demonstrated elsewhere.

Forests are very effective in controlling erosion,

especially if they are undisturbed. The tree canopy

intercepts rainfall and reduces its energy. Drops that

reach the ground are intercepted by the leaf litter and from

there are taken up into the highly porous soil surface.

Removing all vegetation either by burning or clearing and

leaving the soil bare is the worst thing that can happen to

any land surface. When a forest is disturbed by fire, the

natural protection against erosion is destroyed. Extensive

tree removal reduces transpiration and may leave the subsoil

14

perennially wet and impervious. Also, the sun reaching the

soil surface causes rapid decay of organic layers. The

protection of the soil from raindrop impact is taken away

resulting in rapid soil erosion. And therefore by

maintaining high soil fertility, enhanced by decaying

vegetation cover, can prevent soil erosion in many ways

(Stocking, 1988).

The role of vegetation on soil erosion can be concluded as

follows:

It cushions the beating action of falling raindrops.

Offers resistance to moving water and slows down its

rate of flow.

Roots help hold the soil in place, there are

electrochemical, nutrient bonding between root and

soil.

Plant roots and crop residues can improve soil

structure which in turn makes it porous with ability to

absorb water.

Increased faunal and biological activity, leading to

better soil structure.

Greater incorporation of organic matter into the soil,

resulting in better structural and water-holding

qualities.

15

The ability of plants and plant cover to protect the soil

against erosion depends not only on density or thickness but

also on total growth. The greatest protection is obtained

only when the vegetation is vigorous and fast growing.

Edwards and Owens (1991) analyzed 28-year data for nine

small catchment areas under a four-year rotation of maize-

wheat-grass at Coshoctons, Ohio. The results showed that

the three largest storms, all with return period of 100

years or more, accounted for 52 % of the erosion, and 92 %

of the soil loss occurred in the years when the land was

under maize. The effects of desurfacing and natural erosion

on maize grain yield for an Alfisol were studied at Ibadan,

Nigeria (Lal, 1981). The loss of maize grain yield caused

by natural erosion was 0.26 tonnes/ha/mm of eroded soil.

2.3 Soil erosion in Fiji

Soil erosion is a serious problem in the humid tropics. It

is certain to become a greater threat to the economies of

the Region in the near future, as the need to utilise soils

for intensive food production expands.

The effects of soil erosion are both direct and indirect.

Its effects are short term and long term. The soil

depletion, which occurs, leads to lower crop yields due to

losses of essential nutrients and organic matter. The

devastation of the landscape, which takes place, causes a

16

reduction in total productive land area. Watersheds may be

damaged, increased flooding may occur, and deposits of soil

material may be found in waterways, reservoirs and harbours.

All of these contribute to income decline for farmers and

cost increases for local and national governments.

Fiji is the only South Pacific country in which soil erosion

has been treated as a national problem. There is also a

government policy to control it. For many years soil

erosion has been obvious and the country internationally

recognized as having a major soil erosion problem. This

does not mean, however, that the extent, severity and rate

of erosion has been adequately assessed or that adequate

control measures are being implemented.

Soil erosion is not a recent phenomenon in Fiji. It has

exceeded ‘natural’ rates wherever human populations have

exerted pressure on the environment and wherever land

management techniques not attuned to the environment, have

been introduced. Latham and Brookfield (1983) from studies

on the eastern Fiji Island of Lakeba, Anatom in Vanuatu and

Tikopia in Solomons consider that there is evidence of human

induced erosion dating from as early as 3000 years ago.

This evidence was gained from radio-carbon dating of

profiles in swamps within small catchments. The evidence

suggests that human-induced erosion on hill country resulted

in the formation of low-lying alluvial/colluvial deposits.

17

These became the productive agricultural areas, with little

erosion on hill country till after the introduction of new

agricultural crops in the last 100 years. Spriggs (1981)

noted similar occurrences in Anatom (Vanuatu), New Caledonia

and Raratonga in the Cook Islands.

There is evidence that prior to the European influence,

agricultural practices were generally attuned to the

environment, causing little damage to soils. Shifting

cultivation, on the larger islands, seldom over-exploited

the soil resource, as it was concentrated on flat alluvial

soils and steepland colluvial soil, both of which soil

environments had a mechanism for fertility replenishment.

On some of the smaller islands both hilly and easy land (8-

110 slope) were severely depleted indicating that soils were

not ‘renewable’. Repeated burning around defensive hilltop

sites had caused severe soil losses (Twyford and Wright,

1965). Terracing of slopes to provide irrigated land was

practised in a number of areas.

By 1938 soil erosion was sufficiently serious for a

reconnaissance survey of the extent and intensity to be

undertaken by Agriculture and Administrative staff (Harvey,

1949). The survey disclosed that while there was no

widespread erosion it was locally severe in districts where

closely settled immigrant farming populations had become

established. No quantative data was available from the

18

survey, and the only surviving record of it is Harvey’s

paper. In the dry and intermediate rainfall zones

indiscriminate burning and overstocking with cattle and/or

goats was responsible for sheet and gully erosion as well as

for accelerating the destruction of dry zone forests

(Harvey, 1949). Whitehead (1954, p 1-2) gives the following

vivid description – “The burning of the savannah lands has

developed into an annual event, the devastation caused is

plainly visible in the vast areas of Vei Sigasiga “earth to

sky” wastes where the soil has been continuously stripped

and exposed to the onslaught of violent rains. In these

regions only a few inches of sterile subsoil remain”.

In 1965 Twyford and Wright stated that the Land Conservation

Board (set up to deal with problems of soil erosion and land

utilization) considered that about 198,000 acres had

significant potential for erosion because of management

practices being applied, and that a further 107,000 acres of

similar land would be developed in the next 20 years.

The expansion of sugarcane cultivation from alluvial flats

to the rolling and hill country, beginning about 1950,

resulted in soil erosion becoming more severe.

Fiji is unique among sugar producing nations in that over 95

% of the crop is grown by smallholders (Clarke and Morrison,

1987), mostly on short tenure leases. Emphasis is placed on

19

production rather conservation. An example by Morrison

(1981) illustrates this: A World Bank funded development

project at Seaqaqa (Vanua Levu) initiated in the mid-1970s,

expanded sugarcane crops onto nutrient depleted and erodible

latosols on rolling and hilly land. Site observation by

Morrison taken over five years from initial clearing in 1978

to 1983 (on a 50-80 slope) showed 150-200 mm of soil were

lost from upper sections of the site, i.e., approximately

300 t/ha/yr. Soil bulk density increased from 0.85 g/cm3 to

1.10 g/cm3 and organic matter (as % organic carbon) declined

from 4.4 to 3.0 % in the top 120 mm of soil. A serious

decline occurred in the exchangeable bases, calcium and

magnesium, which dropped markedly from 17.9 me/100 g in the

original top 80 mm, to 1.4 me/100 g at 160-250 mm,

indicating a significant decline in fertility as the lower

levels progressively became the surface soil.

On another site near Nadi, on Viti Levu, where a lithosol on

18-220 slope was cleared from a grass/fern/casuarinas cover,

Morrison found 80-140 mm of soil had been lost from sections

of the field by the time of the first harvest. This is

equivalent to a soil loss of about 90 t/ha/yr from scrub

clearance to crop harvest. In some places the whole solum

had been removed. Morrison (1981), using the Universal Soil

Loss Equation (USLE), calculated erosion rates of 36.7

t/ha/yr from a cane field on an 80 slope with reasonably

good cropping practices and located in Fiji’s drier zone.

20

Approximate values used for the USLE calculation were

R = 930 mm;

K = 0.1 (Ferruginous Latosol);

LS = 2.63 (14% slope, 40 m long);

C = 0.3 (good contour practice etc);

P = 0.5 (average value)

giving a calculated rate of soil loss (RKLSCP).

Part of these massive soil losses is due to management, with

cane being harvested towards the end of the dry season.

Cultivating of ratoons at the beginning of the wet season

means that for much of the rainy season the cane provides

very little ground cover.

The USLE estimate of 36.7 t/ha/yr obtained by Morrison

(1981) cannot be taken as more than indicative because it

does indicate soil losses far in excess of the often stated

tropical soil loss tolerance level of 13.5 t/ha/yr suggested

by Hudson (1971). This, together with the measured soil

losses of 300 t/ha/yr and 90 t/ha/yr provide evidence to

indicate present sugarcane management techniques on rolling

and hilly land are environmental disasters in progress.

Sugarcane, though the most extensive crop, is not the most

environmentally damaging. Ginger, recently established in

21

the wetter zone of Viti Levu has management practices, which

actively encourage the destruction of the soil. The need

for effective drainage has resulted in up-slope ridging on

slopes as steep as 380 while bare ground is maintained to

minimise plant competition. Clarke and Morrison (1987)

using the USLE, estimated rates of soil loss to be over 85

t/ha/yr on these lands.

Approximate values used for the USLE calculation were

R = 1530 mm (Nausori);

K = 0.2 (Humic Latosol);

LS = 1.12 (8% slope, 40 m long);

C = 0.5 (average value);

P = 0.5 (average value)

giving a calculated rate of soil loss (RKLSCP). Such rates

will result in a loss of the total solum within 10 years.

Liedtke (1984) using six runoff plots on four types of

crops; sugarcane, dry rice, pine seedlings and pineapple

during a one month period in February 1983, using USLE,

calculated annual soil losses of between 20 and 80 t/ha/yr

(Table 2.1).

Catchment studies of the Ba and Rewa watersheds (Hasan,

1986) indicate annual sediment discharges of the Rewa River

22

at Nausori of 10 x 106 t/yr with sediment concentrations of

from 1 % to 35 % during floods. Hasan estimated the annual

erosion and soil loss rates for the entire Rewa watershed to

be in the order of 3.8 mm/yr or 58 kg/ha/yr. Much of this,

however, probably comes from riverbank erosion or from

debris deposited along the channel, following cyclones; it

cannot be assumed that all is from surface soil losses from

cultivated land.

Table 2.1: Indicating the land use, slope and soil loss from

six plots studied (from Liedtke, 1984).

Runoff plot 1 2 3 4 5 6

Land Use Sugarcane

Drylandrice

Pineseedlings Pineapple

Slope 50 130 110 60 290 50

Condition of surface Ploughed Compact Just

tilled Compact

Soil losst/ha/yr(empiricalvalues based on Morrison 1982)

77.8 77.8 68.8 16.6 4876.5 70.8

23

Chapter 3

MATERIALS AND METHODS

3.1 Trial site

The field experiment was designed to achieve the objective

of determining the effect of soil conservation practice on

soil erosion and its effect on cane and sucrose yields over

three years on a sloping sugarcane farm.

The trial was established at Navoli, Veisaru sector (See

Appendix 5), in Ba on a grower’s farm (Farm #18848) and all

normal cultivation and weeding were carried out by Rarawai

research employees. The trial site was about 12 km North

East of Rarawai Sugar mill. The mill area has an annual

rainfall ranging from 1800 mm to 2600 mm with a mean of 2300

mm. Annual mean average maximum and minimum air

temperatures are 31 and 210C, respectively. The rainy

season is in between the months of November and April which

falls in the warmer months. Cooler months are somewhat

drier than the warmer months with rainfall ranging between

20-30 % of the annual.

24

3.2 Soil sampling

The initial samples were taken at a depth of 0-200 mm to

determine pH, levels of organic carbon (as % organic

matter), available phosphorus, exchangeable bases (K, Ca,

Mg), cation exchange capacity (CEC) and soil texture.

The objective of soil sampling was to obtain a true

representation of the soil properties of the site.

3.2.1 Soil preparation

The soils were air-dried and ground to pass a 2 mm sieve.

The ground samples were put in plastic bags and tightly

secured. These were used for analysis as required.

3.2.2 pH (H2O)

Soil pH was determined in 1:2.5 soil to water suspension

following equilibration for at least 4 hours at constant

room temperature. The pH meter was calibrated using pH 7

buffer, pH 4 buffer and pH 9.2 buffer. The suspension was

stirred by swirling and the pH was recorded (Blakemore et

al. 1981).

25

3.2.3 Exchangeable Ca, K and Mg

Soil (<2 mm, 3 g) was weighed in duplicate into centrifuge

tube and 30 ml NH4OAc (pH 7, 1 mol/L) was added and the

suspension was shaken for 30 minutes in a multi-shaker.

Atomic Absorption Spectrophotometer (AAS) was used to

determine Ca, K and Mg in the filtered solution.

3.2.4 Soil phosphorus (modified Troug)

An air-dried soil sample (1 g) was extracted for phosphorus

with an extracting reagent [50 ml, 0.02 Normal H2SO4 buffered

with ammonium sulphate (3 g/L)]. The soil solution was

shaken for 20 minutes in a Gyrotory shaker and filtered

using Advantec No. 2 paper.

The filtered soil solution (10 ml) was pipetted into a

volumetric flask (50 ml) and distilled water (~30 ml) was

added to it. Troug – Meyer [2 ml, 10 Normal H2SO4 solution

containing ammonium molybdate (2.5 g/100 ml)] was added and

the solution was shaken thoroughly. Stannous chloride (3

drops, 12.5 g SnCl2 in 36 % HCl) was added and then the

solution diluted to mark with distilled water. The

thoroughly mixed solution was allowed to stand for 10

minutes before absorbance readings (within a concentration

curve 0 – 1.6 mg/L P) were recorded in a Hitachi U – 2000 UV

26

– VIS spectrophotometer at 660.0 nm wavelength (Gawander and

Naidu, 1989).

3.2.5 Organic carbon

Soil (1 g, <0.5 mm diameter) was weighed into a 500 ml

conical flask including a reagent blank with the samples and

potassium dichromate solution (0.1667 mol/L, 10 ml) was

added and the flask was gently swirled to wet the sample

thoroughly. In the fumehood, concentrated sulphuric acid

(20 ml) was added and the flask swirled for one minute to

ensure good mixing, not contaminating the sides of the flask

with soil particles.

After allowing the suspension to stand for 30 minutes (200

ml) water was added to the flask, filtered and concentrated

orthophosphoric acid (10 ml) and five drops of diphenylamine

indicator were added to the filtrate. The blank and

filtered samples were titrated with ferrous sulphate (1

mol/L) till the end-point, and the levels of organic carbon

were calculated by Walkley-Black method (Nelson and Sommers,

1982).

27

3.2.6 Soil texture

Soil (50 g, dried overnight at 1050C) was weighed, two

reagent blank and 150 ml of Calgon solution was added and

allowed to stand for 30 minutes. The solution was poured

into the stirring cup and 150 ml of tap water was added.

This was stirred for 5 – 10 minutes with the Hamilton Beach

stirrer at high speed and then transferred to a

sedimentation cylinder. Water was added to the 1130 ml mark

with the hydrometer in position. The mouth of the cylinder

was covered with parafilm and shaken vigorously for 40

seconds. After waiting for 4 minutes the reading was taken

with the hydrometer immersed in the suspended solution and

the temperature was taken accordingly. Similar readings

were taken after two hours (Day, 1965).

3.3 Trial design

For the experiment a 4 x 4 randomised complete block design

was used. The treatments were assigned at random to a group

of experimental units called the block or replication. Each

treatment was assigned once to experimental units within a

block. This was done to keep the variability among the

experimental units within a block as small as possible and

maximise differences among blocks.

28

Figure 3.1: The trial design for the experiment at Navoli,

Veisaru, Ba was a 4 x 4 randomised complete

block design with four treatments replicated

four times randomly. The slope direction is

indicated by arrows marked on the plots.

CANE ACCESS ROAD

Key:

& = Slope Direction

R4 R3 R2 R1

40

20 30 13030

100

20

70

30 20

90

30

90

60

10

30 40

60 60

30

70

70

10

20

60

30

40

30

40

10

70

3m

16T4

9T3

8T2

1T1

15T3 T1

7T4

2T2

14T2

11T4

6T1

3T3

13T1

12T2

5T3

4T4

15m

5m

90

10m 120

29

3.4 Plot layout

The plot size was 150 m2, consisting of seven 1.37 m x 15 m

rows across the field and eleven 1.37 m x 10 m rows uphill

and downhill, with a 3 m (across slope) by 5 m (downhill)

alley separating the ends of all plots.

The plots were bordered at the top and sides to retain

runoff in the plot and direct it to the runoff measuring

equipment. This was done to keep external runoff out of the

plot area. The borders used were galvanised roofing iron

about 30 mm wide buried vertically to about half depth along

the top and sides of the plots.

Runoff contained within the plots by metal borders was

delivered to a collecting trough running full width (15 m)

across the bottom of the plot. The trough was typically of

a cross section 35 mm wide and 25 mm deep. It was buried so

that the uphill entry was exactly level with the natural

soil surface. The eroded soil (the “bed” load) settled out

in the trough for weighing.

30

Figure 3.2: The author with Rarawai employees during initial

stages of trial work at Navoli, Veisaru, Ba. As

indicated by arrows the layout of the trial

shows different planting strategy used in the

study.

Cane planted across field

Cane planted uphill/downhill

31

3.5 Runoff tipping bucket

The tipping bucket used in the study was manufactured from

welded PVC because of its durability and long service life.

This was mounted on a level concrete base and secured by

brass screws. A shade structure with steel roofing was

fitted on the manifold to protect the bucket from sun

damage.

After installation, the capacity of each individual tipping

bucket was determined for use in the calculation of runoff.

This was done using a measuring cylinder of accurately known

volume. Water was poured into one side of the tipping

bucket until it tipped and the volume of water was used.

This was repeated twice for each side and an average value

was determined for calculations.

The tipping bucket counter was used to count the number of

bucket tips to allow calculation of runoff. The counter

used was a sealed magnetically operated mechanical unit.

The magnet was mounted to the tipping bucket and a tip was

registered when the magnet passed behind the counter that

was mounted on the frame.

32

Figure 3.3: Experimental plot showing the arrangement of

tipping bucket, collection trough and manifold

at Navoli, Veisaru, Ba on a sloping cane farm.

Tippingbucket

Collectiontrough

Manifold

33

OUTLET SLOT

FOR RUNOFF

CONCRETE SLAB FOR

TIPPING BUCKET

MANIFOLD

TIPPING BUCKET

SLOPE

ENDPLATE

ENDPLATE

TROUGHSECTIONSOVERLAPPEDBY 50 mm ANDRIVERTED

Figure 3.4: Plan view of runoff collection trough.

34

SOIL SURFACE

COLLECTIONTROUGH

MANIFOLD

RUNOFF

TIPPING BUCKET

CONCRETE SLAB

Figure 3.5: Cross section of the layout.

35

COLLECTION TROUGH

MANIFOLD

END PLATE

MATERIAL1.0 mm GALVANISHEDSTEEL

20mm

THIS LENGTH MAXIMUM POSSIBLE GOVERNED BY BENDING EQUIPMENT (15 m)

360mm

250mm

80mm30mm

1200mm

30mm

20mm

360mm

25mm

BENT 900 AT DOTTED LINE. NEED 3 PER PLOT – ONE FOR EACH END OF COLLECTION TROUGH AND ONE FOR MANIFOLD.

MANIFOLD BENT TO SAME PROFILE AS COLLECTION TROUGH, WITH SLOT TO FEED RUNOFF WATER TO TIPPING BUCKET

Figure 3.6: Cross section of collection trough, manifold

and end plate.

36

3.6 Monitoring of soil loss and runoff

3.6.1 Bed load

These are coarse particles that include sand, silt and

clayey aggregates that roll and saltate over the base of the

flow (Humphreys, 1993).

After a rain event all accumulated sediments in the trough

were collected by wiping with a sponge and oven drying the

sediments collected at 1050C for 24 hours to express bed

load weight.

The total dry weight of the bed load soil was calculated

using the following formula:

D = W * A / B

where:

D is the calculated total dry weight of the bed soil in the

field (kg)

W is the total wet weight of the bed soil from field (kg)

A is the oven dry weight of the soil sub-sample (g)

B is the wet weight of the soil sub-sample (g)

37

3.6.2 Runoff

The runoff data was obtained by multiplying the number of

tips from the tipping bucket counter with the capacity of

the tipping bucket (L).

3.7 Climatic data

A “Monitor Sensors” automatic weather station equipped with

an electronic data logger was used to collect climatic data.

The weather station recorded rainfall, air temperature,

solar radiation and wind speed.

Due to the malfunction of the weather station a manual

rainguage (bottle and funnel type) was installed next to the

data logger rainguage.

3.8 Planting

The trial site was ploughed twice and harrowed in order to

have good soil tilth to a depth of at least 200 mm. The

trial was planted during the replanting season of October

2001. The seedcane was used at the rate of seven tonnes per

hectare. Each stalk will have at least 25 nodes with an eye

bud and root primonida in each node. These were cut into

three node setts normally known as “three-eye” setts. Each

of these setts was planted end to end after dipping in

38

Funginex (Triforine). The number of three-eye setts planted

in each 10 and 15 m length rows was recorded to calculate

the percentage germination. Soon after determining the

germination in each plot, potted single eye-setts was

planted in each plot to have a uniform stand of cane in all

plots.

3.9 Treatments

The treatments used in the plant and ratoon crop are given

in Table 3.1. In the study conducted, Treatment (T) 4 had

trash retained after plant (crop that is planted with fresh

seed and harvested) and ratoon (cultivating the re-growth of

a crop previously harvested, the re-growth takes partial or

total advantage of an existing root system) crop was

harvested.

The other three treatments had trash removed. The reason

being that growers like clean fields so burn the trash and

to avoid young ratoons being damaged by fire. In other

words treatments were chosen according to farmer practice

and are relevant to real farm situation.

39

Table 3.1: Treatment summary for plant and ratoon crop at

Navoli, Veisaru, Ba on a sloping cane farm. In

plant crop, Treatments 1 and 4 were identical

but in ratoon Treatment 4 had trash retained

compared to other three treatments which had no

trash.

Trt Plant crop Ratoon crop

1 Cane planted across slope Cane planted across slope

2 Cane planted uphill and downhill

Cane planted uphill and downhill

3Cane planted across slope with vetiver hedgerow

Cane planted across slope with vetiver hedgerow

4 Cane planted across slope

Cane planted across slope with trash as mulch

3.10 Fertilizer application

Blend A fertilizer was applied at planting and Blend B

fertilizer at 8 eight weeks after planting. In the

subsequent ratoon crop, Blend C fertilizer was applied 4

weeks after harvest at the experiment site.

40

3.11 Weed control

In the trial, herbicides and hand weeding were used to

control weeds. The pre-emergent herbicides Diuron 90 and

Atradex were sprayed at the rate of 3 kg/ha within three

days of planting. This was to control grasses and broadleaf

weeds. However, manual weeding was carried out

approximately ten weeks after planting and just prior to

fertilizer application. Seasonal manual weeding was carried

out when the cane was eighteen to twenty weeks old.

3.12 Crop growth measurement

Within eight weeks of planting the germination in each plot

was determined. Where necessary, potted single eye-setts

were planted to have a uniform number of tillers during the

initial growth period.

When the cane was approximately ten to twelve weeks old,

eight stools were chosen at random from each plot and marked

to determine the number of tillers per stool and height of

stalk. When the crop was twenty weeks old population

counting commenced and continued until it was impossible to

enter the field without damaging the crop.

41

3.13 Harvesting

Sugarcane is generally harvested in Fiji at ten to fifteen

months after planting. Plant cane requires a little longer

growing period than the ratoon crop. The plant cane was

harvested when the crop age was approximately thirteen

months. However, the ratoon crop was harvested when the

crop age was twelve months.

In each plot all the rows were harvested and manually

weighed. This was used to determine the yield per unit

area.

3.14 Cane juice analysis

Cane samples consisting of nine stalk samples were taken at

random from each plot for cane juice analysis. The whole

cane stalks were ground in the disintegrator and mixed

thoroughly. A 500 g sample was pressed in a hydraulic press

and juice extracted at 510 Pa pressure. The juice was

filtered through lead acetate and polarization readings were

taken using a Polartronic MHZ polarimeter and brix was

measured using a DUR-SW refractometer. To determine the

fresh fibre weight, a 100 g sample was weighed.

The pol, brix and fibre values were used to determine the

%Pure Obtainable Cane Sugar (%POCS) as described by Powell

42

(1955). The product of cane yield per unit area and %POCS

gave total tonnes sugar per hectare.

3.15 Statistical analysis

All data were analysed by standard ANOVA procedures using

the STATISTIX8 statistical package.

43

Chapter 4

RESULTS

4.1 Soil type and analysis

Primary characterisation data for soil chemical and physical

properties are given in Tables 4.1 and 4.2 respectively.

The initial chemical analysis indicates that soil is

moderately acid, contains high levels of major nutrients and

has low content of organic matter.

Horizon A (0-20 cm) in textural class was characterised as

sandy clay loam. The soil profile description is given in

Appendix 4A and illustrated graphically in Appendix 4B.

Results of the analyses of the topsoil taken after harvest

of plant, first and second ratoon crop are shown in Appendix

3A, 3B, 3C and illustrated graphically in Figures 4.1, 4.2,

4.3, 4.4, 4.5 and 4.6 where pH(H2O), organic matter,

available P and exchangeable K, Ca, Mg, respectively, are

plotted against time (cropping season) after sugarcane was

planted. Significant changes occurred at the trial site and

differences were observed between the three cropping

seasons.

44

Figure 4.1: Variation in the pH with time (P-plant crop, R-

first ratoon, S-second ratoon) after initial

land preparation. Plotted data are the means of

four measurements. Details on the respective

treatments are presented in Table 3.1.

4.9

5.1

5.3

5.5

5.7

5.9

6.1

6.3

I P R S

pH

T1 T2 T3 T4

45

Figure 4.2: Variation in the OM with time (P-plant crop, R-





1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

I R S

OM%

T1 T2 T3 T4

46

Figure 4.3: Variation in the P with time (P-plant crop, R-





80

130

180

230

280

330

I P R S

P mg/kg

T1 T2 T3 T4

47

Figure 4.4: Variation in the K with time (P-plant crop, R-





150

200

250

300

350

400

I P R S

K mg/kg

T1 T2 T3 T4

48

Figure 4.5: Variation in the Ca with time (P-plant crop, R-





2000

2200

2400

2600

2800

3000

3200

I P R S

Ca mg/kg

T1 T2 T3 T4

49

Figure 4.6: Variation in the Mg with time (P-plant crop, R-


land preparation. Plotted data are the means

of four measurements. Details on the

respective treatments are presented in Table

3.1.

500

550

600

650

700

750

800

I P R S

Mg mg/kg

T1 T2 T3 T4

50

Table 4.1: Chemical characteristics (initial) of Navoli soil

collected from a depth of 0-200 mm. Soil

analyses included pH, OM, available P,

exchangeable bases and cation exchange capacity

(CEC).

ExchangeableBases

(mg/kg)Location Depth

(mm)

pH

(H2O)

OM

%

Mod.Troug P(mg/kg)

K Ca Mg

CECcmol(+)/kg

Navoli,Veisaru, Ba

0-200 6.1 2.5 197 230 2705 650 23.6

Table 4.2: Physical Characteristics of Navoli soil collected

from a depth of 0-200 mm. Characteristics

included % sand, silt, clay and textural class.

Texture

Location Depthmm % sand % silt % clay

Texturalclass

Navoli,Veisaru,

Ba0-200 48 21 31 Sandy

clay loam

51

4.2 PLANT CROP

4.2.1 Germination

Germination is percentage of primary shoots that emerge from

the total buds in the planting material. The total number

of three-eye setts (stalk cuttings) planted in each plot was

recorded at the time of planting.

In each plot at eight weeks of planting, percent germination

was determined. The results are summarised in Table 4.3.

Treatment 2 had highest germination (71 %) but due to low

germination in Rep 1 and 3 overall mean was affected.

Similarly, Treatment 3 was affected due to low germination

in Rep 1 and 2 which had Standard Error of Mean (SEM) as

8.8. Treatment 1 had 61 % germination because of very low

(38 %) germination in Rep 2. The SEM was 8.5. Overall

germination in Treatment 4 was lowest (58 %) of the lot with

SEM as 1.3.

Due to high intensity rainfall after planting some three-eye

sett pieces were washed away and single eye-sett potted

plants were planted in the gaps to achieve uniform plant

population in each plot.

52

Table 4.3: Germination count taken at 8 weeks of planting in

each plot at Navoli, Veisaru, Ba. Details on

the respective treatments are presented in Table

3.1.

Treatment Replication 3 eye-sett planted

Population %germination

1111

Mean

1234

491561481584

529

111363310361064

962

76387261

61

2222

Mean

1234

502394581500

494

100599610621116

1045

67846174

71

3333

Mean

1234

501447447523

480

71971010421304

944

48537883

66

4444

Mean

1234

402551499541

498

714915915941

871

59556158

58

53

4.2.2 Tillers per stool

Tillering refers to the number of shoots per stool

originating from the one three-eye sett. Shamel (1924)

reported that as many as 144 stalks were recorded in a stool

arising from a one bud sett.

During the early growth period the number of tillers per

stool varies between 15 and 20 depending on the cane

variety. There was no significant increase in the number of

tillers per stool for different treatments at various months

of crop age. At seven months of age, the number of millable

stalks stabilised at 3-4 (Table 4.4).

4.2.3 Stalk length

Stalk length is determined by measuring the distance between

the ground level and up to the top visible dewlap leaf

(TVD).

The rainfall distribution from February to May 2002 was

favourable to cane growth. A total of 1016 mm rainfall was

received during the four-month period with the highest of

464 mm in March 2002 and lowest of 83 mm in April 2002.

The most rapid stalk elongation period for the plant crop

occurred when crop age was four to five months (Table 4.4),

which coincided with high rainfall and maximum temperature

54

as highlighted in Table 4.7. The average elongation rate

during this period was 19 mm/day compared to 16 mm/day

between March to April and 9 mm/day between April to May.

The latter was due to low rainfall and cooler night time

temperature after April which affected vegetative growth of

the sugarcane plants.

After April the rainfall and air temperature decreased with

time and sugarcane entered the ripening period. The monthly

rainfall and the maximum and minimum temperature in pre-

crushing period of April, May and part of June are the most

important factors affecting sugar content in the early

crushing season. For example, in 1994 Fiji Sugar

Corporation made record sugar of 516 529 t from 4.06 million

tonnes of cane with a tcts (Tonnes Cane/Tonnes Sugar) ratio

of 7.86 (FSC, 2002). This was largely attributed to dry

conditions in April and May (i.e. 122 mm of rain from 7

raindays) which improved pocs levels. The average for the

season was 13.3 % whereas mills commenced with a pocs of

little over 11 instead of slightly greater than 10 in other

years.

Therefore it is easier to manipulate the cane yield than

%pocs values on the farm. This is because maturity in a

rainfed industry is more dependent on weather during the

short maturing period than cane growth which takes place 12-

15 months. In the case of cane growth it can be manipulated

55

by irrigation, fertilization, weed control and cultural

practices.

Recent preliminary studies indicated that rainfall of April,

May and June were strongly correlated to cane production.

That is, the cane production for a year has direct

correlation (Spearman Rank correlation) with moving average

rainfall of these months (Gawander, unpublished data). The

Sugar Technical Mission of the Republic of China to Fiji

(1996) found that average tonnage increase was approximately

10-12 t/month in the rapid growth stage from January to May.

The analysis of variance showed that different planting

strategies associated with conservation practice did not

significantly (P>0.05) increase stalk length measured at

four, five, six and seven months of crop age.

4.2.4 Stalk population

The results of observations on stalk population are given in

Table 4.7. In the early growth stages, at four months of

age, uphill and downhill plot had the highest population

followed by vetiver hedgerow plot. This was due to the

extra (5 m) of cane planted in uphill and downhill plot (11

rows x 10 m) compared to other plots (7 rows x 15 m, across

the field). Thus cane planted across the field had lower

56

population but then stabilised (79,000 stalks/ha) at seven

months of age.

The trial did not show any significant difference between

treatments in stalk population at four, five, six and seven

months of crop age. In all treatments, the number of stalks

per unit area decreases with age of crop due to mortality of

weaker tillers within a stool.

57

Table 4.4: Periodic measurements taken at 4, 5, 6 and 7

months included tiller and population count, and

stalk height measurement. Details on the


3.1.

Stalk

Tillers per stool

Population(x103 ha-1) Length (m)

Month Month Month

Treatment

4 5 6 7 4 5 6 7 4 5 6 7

1

2

3

4

5

5

6

6

4

4

4

4

3

3

4

4

3

3

4

4

130

150

137

134

83

88

86

86

83

86

85

85

78

79

80

78

0.95

1.03

0.99

0.92

1.61

1.60

1.61

1.55

2.27

2.26

2.27

2.22

2.56

2.69

2.57

2.51

Rainfall(mm) 347 439 83 122

LSD 5%

CV%

NS

18

NS

17

NS

25

NS

25

NS

8

NS

6

NS

3

NS

3

NS

9

NS

7

NS

5

NS

5

Months: 4 – February, 5 – March, 6 – April, 7 – May

NS not significant

CV coefficient of variation

58

4.2.5 Cane and sucrose yield

Throughout the studies, sugarcane yields are expressed as

tonnes of sugarcane per hectare (tcha-1). Effort was made to

harvest crop at a similar age for both plant and ratoon

crops. The reason being that sugarcane is a vegetative

product and the rate of growth is not uniform. Generally,

the rate of elongation during December to April, which is

the wet season in Fiji, is about twice that during the rest

of the year.

It is worth noting that Treatments 1 and 4 are identical

i.e. both treatments were planted across the slope, but in

ratoon crop Treatment 1 had trash removed and Treatment 4

had trash retained as mulch.

Responses to different treatments in terms of cane and sugar

yield are summarised in Table 4.5 and illustrated

graphically in Figure 4.7 and 4.8 respectively. The results

indicated that there were significant differences among

treatments for cane and sugar yield at 5 % level.

A step further, using Tukey’s all-pairwise comparisons test

for cane yield showed that Treatment 2 is significantly

different from Treatment 1 but not from Treatments 3 and 4

(Table 4.6). Similarly Treatment 3 was significantly

different from Treatment 1 but not from Treatments 2 and 4.

59

In the study Treatments 2 (cane planted uphill and downhill)

and 3 (cane planted across slope with vetiver hedgerow)

produced significantly higher cane yield than Treatment 1

(cane planted across slope). The high cane yield recorded

in Treatment 2 may have resulted as explained earlier in

section 4.2.4. The test with sugar yield showed that there

are no significant pairwise differences among the means

(Table 4.6).

Table 4.5 shows that different planting strategies

associated with conservation practice did not affect

(P>0.05) sucrose level in Naidiri variety. As anticipated

Naidiri is a high sugar variety, subsequently high cane

yield resulted in high sugar yield per unit area.

The low % CV’s (less than 10) for %pocs, cane and sugar

yield shows that the statistical design was sound as it

reduced the variability from the study.

60

Table 4.5: Effect of different planting strategies

associated with conservation practice in

plant crop at Navoli, Veisaru, Ba on a Sandy

clay loam soil. Plotted data are the means

of four measurements.

CaneYield

(tcha-1)

POCS(%)

SugarYield

(tsha-1)

Treatment

(Planting strategy associated with conservation practice)

P P P

1. Cane planted across slope

2. Cane planted uphill and downhill

3. Cane planted across slope + vetiver hedgerow


106

119

117

110

17.7

17.5

17.6

17.5

18.7

20.7

20.6

19.2

LSD 5%

CV%

7.5

4

NS

1

1.6

5

tcha-1 tonnes cane per hectare

tsha-1 tonnes sugar per hectare

P plant crop

NS not significant


61

Table 4.6: Tukey’s all-pairwise comparison test of cane and

sugar yield in plant crop. Means followed by a

common letter are not significantly different at

5 % level of significance.

Tukey HSD All-Pairwise Comparisons Test of tcha-1 for treatment

Trt Mean Homogeneous Groups 2 118.50 A 3 116.75 A 4 110.00 AB 1 106.00 B

Alpha 0.05 Standard Error for Comparison 3.3380 Critical Q Value 4.418 Critical Value for Comparison 10.428 Error term used: block*trt, 9 DF

Tukey HSD All-Pairwise Comparisons Test of tsha-1 for treatment

Trt Mean Homogeneous Groups 2 20.650 A 3 20.550 A 4 19.200 A 1 18.700 A

Alpha 0.05 Standard Error for Comparison 0.6530 Critical Q Value 4.418 Critical Value for Comparison 2.0399 Error term used: block*trt, 9 DF

62

Figure 4.7: Histogram showing the means of tonnes cane per

hectare (tcha-1) for each of the four treatments

in plant crop. Plotted data are the means of

four measurements.

LSD0.05=7.5

63

Figure 4.8: Histogram showing the means of tonnes sugar per

hectare (tsha-1) for each of the four

treatments in plant crop. Plotted data are

the means of four measurements.

LSD0.05=1.6

64

4.2.6 Runoff and soil loss

The results show that surface runoff was closely related to

rainfall and was affected to a great extent by soil surface

condition associated with the planting strategy. The

results are summarised in Table 4.8 and illustrated

graphically in Figure 4.9. The month of January recorded

highest accumulated surface runoff (6533 m3ha-1yr-1) compared

to the rest of the year as shown in Appendix 2A. The

rainfall in December 2001 is likely to have saturated the

soil which resulted in greater runoff in January whereas

establishment of leaf canopy reduced runoff volume in

February and March 2002, which experienced higher rainfall

than January. Chapman (1948) explained that a canopy

intercepts raindrops before they reach the ground. Some of

the intercepted water evaporates before it reaches the

ground, some flows down the cane stalk and adds to runoff

but causes no detachment by drop impact, and some drops

reform and fall to lower plant surfaces or to the ground.

Drops that fall from plant surfaces are usually larger than

natural raindrops.

Uphill and downhill treatment had the highest runoff, 6774

m3ha-1yr-1, which accounted for 32 % of total rainfall.

Treatments where cane was planted across the slope, with and

without vetiver hedgerow slowed movement of water downward,

65

thus recorded less runoff. This ranged from 3830 to 4670

m3ha-1yr-1.

The planting strategy was the dominating factor affecting

the volume of runoff in the study. Across the field

planting which slows the water movement downwards and acts

as a barrier had runoff considerably less than that of

uphill and downhill plots (Figure 4.9). Vegetation

intercepted rainfall and retarded overland flow, thus

reduced runoff volume.

A similar pattern to that of runoff was observed for soil

erosion. During the early growth period before close-in of

the canopy, the soil surface was exposed directly to the

impact of raindrops. This resulted in high rates of

erosion. This was especially true in plant crop because the

surface soil was soft and loose after planting operations.

It was evident as high rainfall in December 2001 (200 mm),

January and February 2002 (271 and 347 mm) respectively,

resulted in progressively higher soil loss. The month of

February was outstanding in terms of soil eroded

(16.9 tha-1yr-1) as given in Appendix 2A. The most effective

control was with vetiver hedgerow planted across the slope

on the lower end of the plot. Thereafter soil surface

stabilised after erosion of loose soil as illustrated in

Figure 4.10.

66

Table 4.6 shows that total soil loss expressed on oven-dry

weight basis was greatest from the treatment which had

furrows running uphill and downhill, 16.4 tha-1yr-1, followed

by cane planted across the slope, 10.1 and 9.7 tha-1yr-1. The

least erosion was from cane planted across the slope with

vetiver hedgerow (7.1 tha-1yr-1). This represented only 43 %

loss in comparison with furrows running uphill and downhill.

The results clearly indicated that vetiver technology

effectively reduced the amount of soil eroded in the plant

crop.

67

Figure 4.9: Surface runoff affected by different planting

strategies associated with conservation

practice in plant crop at Navoli, Veisaru, Ba

on a sloping cane farm. Plotted data are the

means of four measurements.

Runoff expressed as m3ha-1yr-1

Rainfall expressed as millimetres (mm)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

dec_01 jan_02 feb_02 mar_02 apr_02 may_02 jul_02 aug_020

50

100

150

200

250

300

350

400

450

500Cane planted uphill/downhill

Rainfall

Cane planted across slope (T1)

Cane planted across slope + vetiverhedgerow


SURFACE

RUNOFF

RAINFALL

MONTHS

68

Figure 4.10: Soil erosion affected by different planting


practice in plant crop at Navoli, Veisaru, Ba

on a sloping cane farm. Plotted data are the


Soil loss expressed as kgha-1yr-1


500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

dec_01 jan_02 feb_02 mar_02 apr_02 may_02 jul_02 aug_020

40

80

120

160

200

240

280

320

360

400

440

480

520

560 Cane planted uphill/downhill

Rainfall


Cane planted across slope + vetiver hedgerow


RAINFALL

SOIL

LOSS

MONTHS

69

Table 4.7: Rainfall and average temperature summary for

plant crop.

Temperature 0CMonth Rainfall

(mm)Raindays

Max Min

19 Oct 01

183 3 29.5 21.4

Nov 85 4 32.1 21.0

Dec 200 10 32.7 21.9

Jan 271 15 32.4 23.5

Feb 347 17 32.7 23.8

Mar 464 17 32.4 22.8

Apr 83 12 32.1 22.8

May 122 7 30.2 21.7

Jun 45 2 31.0 18.1

Jul 87 7 29.5 19.1

Aug 60 9 28.8 17.8

Sep 145 7 30.3 19.7

30 Oct 02 48 7 31.3 20.3

Total 2140 117 31.1 21.1

70

Table 4.8: Summary of surface runoff and soil loss affected

by different planting strategies associated with

conservation practice in plant crop at Navoli,

Veisaru, Ba on a sloping cane farm.

Surface runoff Soil loss

Treatments

m3ha-1yr-1% of total

rainfallkgha-1yr-1 tha-1yr-1

T1 – cane planted across slope 4485 21 10101 10.1

T2 – cane planted uphill/downhill 6774 32 16376 16.4

T3 – cane planted across slope +

vetiver hedgerow 4670 22 7065 7.1


Rainfall (mm) 2140

71

4.3 FIRST RATOON CROP


Responses in terms of cane and sucrose yield are summarised

in Table 4.9. The results showed that experimental

treatments used in the study did not affect (P>0.05) cane

and sugar yield. However, the treatment with trash

conserved as mulch produced higher (4-11 %) cane yield in

comparison to other treatments investigated in the study.

In terms of dollar value this would equate to additional

income (F$150-$400) for the grower. Surprisingly, treatment

where cane was planted across slope with vetiver hedgerow

produced least cane and sugar yield. This was most likely

due to low germination (%) in Rep 1 and 2 that affected

treatment yield (See Table 4.3).

The results of the first ratoon crop shows that uphill and

downhill treatment had the lowest %pocs in comparison with

other three treatments, however it was not significantly

different from other treatments (Table 4.9). A similar

result was obtained in plant crop for uphill and downhill

planting which indicated that it is important to conserve

trash on a sloping farm in order to sustain production level

and remain economically viable in future. A unit decline in

%pocs has direct impact on sugar made at the mills and the

revenue generated from sale of raw sugar.

72

The cane and sugar yield declined in the first ratoon

compared to plant crop due to low rainfall recorded at the

trial site, especially during the active growth period i.e.

from November 2002 to February 2003 (Table 4.10).

Observations revealed that the crop experienced moisture

stress in the early growth stages. The early drying off

period may have caused high sucrose accumulation resulting

in greater %pocs (18.3-19.3) than plant crop which ranged

from (17.5-17.7) but overall reduction in cane yield led to

decline in sugar produced.

73



first ratoon crop at Navoli, Veisaru, Ba on a

Sandy clay loam soil. Plotted data are the


CaneYield

(tcha-1)

POCS(%)

SugarYield

(tsha-1)

Treatment


R R R




4. Cane planted across slope + trash mulch

79

77

74

82

19.0

18.3

18.5

19.3

15.0

14.1

13.6

15.9

LSD 5%

CV%

NS

10

NS

3

NS

9



R first ratoon crop

NS not significant


74

4.3.2 Runoff and soil loss

Due to low rainfall in 2003 (1007 mm) runoff and soil loss

decreased considerably in all plots compared to previous

season. The results of first ratoon crop are summarised in

Table 4.11.

The month of March recorded highest accumulative runoff

volume (1809 m3ha-1yr-1) as shown in Appendix 2B, which

coincided with high rainfall (423 mm). Thereafter, runoff

decreased as less rain was recorded at the trial site as

shown in Figure 4.11. Table 4.11 shows that treatment with

trash mulch had least runoff compared to other three

treatments that had trash removed. The trash cover

increases hydraulic roughness, causing reduced flow velocity

and increased flow depth to protect the soil from impacting

raindrops. Increased flow depth on 0.7 m long interrill

plots covered with straw mulch decreased interrill erosion

by 20 % for a 25 % ground cover, by 44 % for 61 % cover and

by 77 % for 90 % cover over (Foster, 1982a).

The vetiver hedgerow that was planted across the field acted

as a barrier and retarded water movement downhill. Where

sugarcane was planted uphill and downhill the treatment

recorded highest runoff (1170 m3ha-1yr-1 or 117 mm). It was

equivalent to 12 % of total rainfall and approximately three

times more than treatment with trash mulch. The finding

75

clearly demonstrates the advantage of retaining trash after

harvesting successive crops.

A similar relationship was observed with soil loss. Table

4.11 shows the treatment with trash mulch had the least soil

loss (153 kgha-1yr-1) compared to Treatments 1 (cane planted

across slope), 2 (cane planted uphill and downhill) and 3

(cane planted across slope with vetiver hedgerow).

Treatment 1 recorded highest soil loss (375 kgha-1yr-1) due to

no protective cover against rain. The sudden increase in

soil erosion in May 2003 (Figure 4.12) may be explained as

high rainfall in March washing away the loose soil whereas

rain in April is likely to have saturated the soil and

caused greater soil erosion in May than April 2003. The

relatively dry period experienced from June until the

harvest (October 2003) had no sediment loss. Table 4.10

shows the summary of rainfall data from October 2002 to

October 2003.

It would be interesting to note if this would be the case

during high rainfall year. The results clearly demonstrated

the importance of trash cover or mulch for crop growth and

cane and sugar yield on a sloping cane farm.

76

Figure 4.11: Surface runoff affected by different planting


practice in first ratoon at Navoli, Veisaru,

Ba on a sloping cane farm. Plotted data are


Runoff expressed as m3ha-1yr-1


0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

jan_03 feb_03 mar_03 apr_03 may_030

32

64

96

128

160

192

224

256

288

320

352

384

416

448

480

Rainfall

Cane planteduphill/downhill

Cane planted across field + trash mulch

Cane planted across slope


SURFACE

RUNOFF

RAINFALL

MONTHS

77



practice in first ratoon at Navoli, Veisaru,

Ba on a sloping cane farm. Plotted data are




0

20

40

60

80

100

120

140

160

jan_03 feb_03 mar_03 apr_03 may_030

60

120

180

240

300

360

420

480Cane planted across slope

Cane planted uphill/downhill


Cane planted across slope + trash mulch

Rainfall

SOIL

LOSS

RAINFALL

MONTHS

78

Table 4.10: Rainfall summary for first ratoon crop at

Navoli, Veisaru, Ba.

Month Rainfall(mm) Raindays

31 October 2002 - -

November - -

December - -

January 58 7

February 146 8

March 423 10

April 226 7

May 81 5

June 27 2

July - -

August 46 3

September - -

22 October 2003 - -

Total 1007 42

79

Table 4.11: Summary of surface runoff and soil loss affected

by different planting strategies associated with

conservation practice at Navoli, Veisaru, Ba on a

sloping cane farm.

Surface runoff Soil loss

Treatments

m3ha-1yr-1% of total

rainfallkgha-1yr-1 tha-1yr-1


T2 – cane planted uphill/downhill 1170 12 259 0.26


vetiver hedgerow 851 8 248 0.25

T4 – cane planted across slope + trash mulch

434 4 153 0.15

Rainfall (mm) 1007

80

4.4 SECOND RATOON CROP

4.4.1 Growth measurement parameters

The growth measurement data presented in Table 4.12 showed

that treatment where cane was planted across slope with

trash mulch (T 4) had higher number of tillers per stool (3)

and stalk population (79 000) at nine months of crop age

(final reading) compared to other three treatments, which

resulted in higher cane yield. In plant and second ratoon

crop treatment where cane was planted uphill and downhill (T

2) had greater population in the initial stages of growth

but stabilised prior to harvest in relation to other

treatments investigated in the study. A notable change in

the number of tillers was observed for second ratoon crop

which decreased from six to two per stool. In the plant

crop the number of tillers per stool was in the range (3-4).

The decrease in second ratoon crop is likely to affect cane

and sugar yield, which is of concern to growers because less

number of millable stalks equates to low cane yield per unit

area. This will eventually reduce grower’s profit margin

and the variety may lose its preference amongst other early

maturing commercials such as Aiwa, Beqa and Kaba. According

to FSC (2004) annual report Naidiri crushed was 3.9 % of all

cane crushed (3,001,189 tonnes from 60,080 ha). Of all the

commercial varieties (15) available for planting, Mana is

81

the dominant variety in the Fiji sugar industry and accounts

for 64% of the total area under cane. For any variety to

have significant impact it ought to be better than those

which have been accepted by growers in terms of area under

cultivation. This may be a challenge for plant breeders to

see where improvements could be made for future varieties.

82

Table 4.12: Periodic measurements taken at 3, 5, 7 and 9

months included tiller and population count,

and stalk height measurement. Details on the


3.1.

Stalk

Tillers per stool

Population(x103 ha-1) Length (m)

Month Month Month

Treatment

3 5 7 9 3 5 7 9 3 5 7 9

1

2

3

4

6

6

6

5

3

3

3

3

2

3

2

3

2

2

2

3

102

105

96

98

86

87

81

83

79

79

75

85

73

73

70

79

0.89

0.86

0.84

0.94

1.64

1.60

1.56

1.69

2.12

2.02

2.01

2.30

2.29

2.17

2.14

2.31

LSD 5%

CV%

0.7

7

NS

16

NS

21

NS

30

NS

4

NS

7

NS

6

NS

2

NS

10

NS

5

NS

5

NS

3

Months: 3 – January, 5 – March, 7 – May, 9 – July

NS not significant


83


Table 4.13 shows that conservation practices used in the

study did not affect (P>0.05) cane and sugar yield. In the

second ratoon crop, the cane yield was 84, 70, 69 and 64

tcha-1 respectively from the following treatments: cane

planted across slope with trash, cane planted across slope,

cane planted uphill and downhill, and cane planted across

slope with vetiver hedgerow. Treatment where trash was

conserved in the plot produced 14-20 tcha-1 or 20-31 % more

cane than the other three treatments. In terms of

additional revenue, the grower would earn F$700-$1000 (based

on average cane price of $50/t) by following correct

cultural practice compared to other practices as

investigated in this study.

The combined yield from the plant, first and second ratoon

crops was 276 tonnes cane from the trash conserved treatment

being 8 % higher than cane planted across slope without

trash and cane planted across slope with vetiver hedgerow.

Similarly it was 4 % higher than the treatment where cane

was planted uphill and downhill without trash. Of the three

years, the rainfall experienced during the first ratoon

cropping season was 43 % of the long term average (2316 mm)

for Rarawai mill area.

84

The results obtained from this study clearly showed that

under rainfed agriculture in Fiji the most effective and

practical way for water and soil conservation on a sloping

farm is to plant cane across the slope and practise trash

mulch. The practice does not only reduce movement of water

downward but also protect surface from direct impact of

raindrops. The strategy can be adopted with very low cost

due to the fact that no cultivation is required under trash

conservation condition. Through reduction in runoff and

soil erosion, sugarcane crop could obtain more water and

nutrients for its growth resulting in a higher yield per

unit area.

85



second ratoon crop at Navoli, Veisaru, Ba on

a Sandy clay loam soil. Plotted data are the


CaneYield

(tcha-1)

POCS(%)

SugarYield

(tsha-1)

Treatment


S S S




4. Cane planted across slope + trash mulch

70

69

64

84

16.5

17.0

16.9

16.7

11.7

11.8

11.8

14.0

LSD 5%

CV%

NS

14

NS

4

NS

15



S second ratoon crop

NS not significant


86

4.4.3 Soil loss

Table 4.15 shows that soil loss was 2.5 tha-1yr-1 in the

treatment where cane was planted across slope and least from

the treatment that had trash retained as mulch

(0.22 tha-1yr-1). The excessive soil loss recorded in plot 13

contributed to high erosion rate in Treatment 1. This was

caused by water retention in the sub-surface layer as

indications are that the plot area was filled by soil

(depression at the site) before cane was actually planted.

Even after low rainfall surface layer became saturated

quickly, resulting in high velocity of water moving downward

with soil in a short period of time. As illustrated in

Figure 3.1 plot 13 had three-way slope and the gradient

being higher diagonally, running downwards caused increased

sediment loss.

After eliminating plot 13 from initial calculation, uphill

and downhill treatment proved to be the least desired

strategy for planting cane on a sloping land which not only

had greater soil loss but more importantly affected cane

yield.

In addition to the best management practice of cane planted

across slope with trash mulch, results presented in Table

4.13 and illustrated graphically in Figure 4.13 indicated

87

that vetiver hedgerow planted on the sloping end of the plot

acted as barrier against water and soil movement. The two

practices (trash mulch + vetiver hedgerow) if combined

together can provide effective control over soil erosion on

undulating and hilly terrains.

The graph as illustrated in Figure 4.13 shows that soil loss

continued to decrease over the time period. Table 4.14

shows that high rainfall in December 2003 (427 mm in 19

days) washed away the loose soil that may have resulted from

the harvesting operations. In January 2004 soil loss

decreased in all plots due to low rainfall (52 mm) whereas

high rainfall in February and March (greater than 400 mm per

month) did not result in excessive soil loss due to

establishment of canopy cover. As observed there was no

direct relationship between soil loss and rainfall.

It is important to practise trash mulching on hilly lands

because cane which is harvested late in the season is prone

to high intensity rainfall in wet season. This may be

contributing to declining cane yields and necessitates use

of high rates of chemical fertilizer to sustain production

level.

It is worth mentioning at this juncture that due to

financial constraint analyses of bed load samples (soil

88

collected from collection troughs after each rain event)

could not be carried out to quantify nutrient loss. The

samples are securely stored at the Sugarcane Research Centre

and will be analysed once the funds are made available.

89



practice at Navoli, Veisaru, Ba on a sloping

cane farm. Plotted data are the means of

four measurements.



0

100

200

300

400

500

600

700

dec_03 jan_04 feb_04 mar_04 apr_04 jul_04 aug_040

100

200

300

400

500

600

700Cane planted uphill/downhill

Cane planted across slope


Cane planted across slope + trash mulch

RainfallSOIL

LOSS

RAINFALL

MONTHS

90

Table 4.14: Rainfall summary for second ratoon crop at

Navoli, Veisaru, Ba.

Month Rainfall(mm) Raindays

22 October 2003 - -

November 64 8

December 427 19

January 52 9

February 481 18

March 427 18

April 157 7

May 54 4

June 100 8

July 128 3

August 378 12

September 63 6

October 21 6

18 November 2004 1 1

Total 2351 119

91

Table 4.15: Summary of soil loss affected by different

planting strategies associated with

conservation practice at Navoli, Veisaru, Ba

on a sloping cane farm.

Soil loss

Treatments

kgha-1yr-1 tha-1yr-1

T1 – cane planted across slope 2498 2.5

T2 – cane planted uphill/downhill 2274 2.3


vetiver hedgerow393 0.4

T4 – cane planted across slope + trash mulch

221 0.2

Rainfall (mm) 2351

Note: Calculation of runoff was affected because five tipping buckets were stolen during the season.

92

Chapter 5

DISCUSSION

5.1 Top-soil samples

5.1.1 Soil pH

The pH(H2O) of the soil samples decreased from 6.1 to 5.0,

5.3, 5.1 and 5.5 for Treatments 1, 2, 3 and 4 respectively

with increasing period of cultivation as shown in Appendix

3A, 3B and 3C. Trash retained plots (T 4) were less

affected as compared to other three treatments.

Changes in soil pH can be influenced by the organic matter

content with subsequent effects on ion exchange properties

and buffering capacity, the addition of fertilizers

(acidification due to reaction: NH4

+ + 202 = NO3

- + H2O + 2H+)

and the addition of bases such as Ca and K from blended

fertilizers (Masilaca et al. 1986). The decrease in pH

observed could be due to a combination of the decrease in

organic matter content (refer to section 5.1.2), addition of

N fertilizers, and removal of bases (Ca, Mg, K and Na) in

harvested cane.

93

5.1.2 Organic matter

There was a gradual decline in organic matter (OM) content

following initial land preparation, as would be expected

with the disturbance of a stable soil and vegetation. The

OM content fell from 2.5 % to 1.9 % after three years, which

was equivalent to 33 % decrease where cane was planted

uphill and downhill. The decline in OM content of soils may

be attributed to the increased mixing and aeration of soils

which enhanced mineralization of liable OM. Similar changes

in OM content of soils have been reported by many previous

investigators under conventional tillage systems (Cameron

and Wild, 1984; Morrison et al. 2005)

5.1.3 Available P

The P values remained relatively high with increasing period

of cultivation. Addition of P fertilizer in the plant crop

increased P in Treatments 1 and 2, then declined in the

first ratoon crop but remained comparatively higher than

Treatments 3 and 4. No full explanation for these changes

is immediately apparent but amounts of P added as

fertilizers are very small compared with the total P already

present in the surface layer.

94

5.1.4 Exchangeable K

There was a general increase in K with increasing period of

cultivation (refer to Figure 4.4). The results indicate

that soil had high reserve of K and addition of fertilizers

enhanced K availability in the soil.

In trash retained plot K was higher than other three

treatments indicating that trash (cane tops) provided added

benefit in terms of K available for plant uptake. Gawander

(1997) in his studies on the nutrient budget found that K

uptake by cane tops was 85 kg K ha-1 when 250 kg K was added

as fertilizer. Hence a substantial quantity of K was

returned with sugarcane residues as observed in trash

conserved plot (T 4).

5.1.6 Exchangeable Ca + Mg

The Ca and Mg values decreased at the trial site with

increasing period of cultivation (refer to Figures 4.5 and

4.6). This indicates that bases were being lost by

leaching, erosion and crop removal.

The sugarcane cultivars grown in Fiji are fast-growing and

known to deplete soils of bases very rapidly as this was

particularly significant in soils with minimal reserves of

bases (Krishnamurthi, personal communication in Masilaca et

95

al. 1986). Humbert (1968) estimates crop removal values of

25-45 kg Ca ha-1 crop-1 whereas Ca additions via fertilizers

were approximately 40 kg ha-1 for the plant crops and 20 kg

ha-1 for the ratoon crops. In ratoon crops, the fertilizer

was applied as a top dress, some which could have been

washed away under high intensity rainfall. Thus it is

likely that more bases were removed in harvesting than were

added in fertilizers.

5.2 Climatic conditions

The plant and second ratoon crop received rainfall similar

to long term (117 years) average of 2316 mm for Rarawai mill

area compared to first ratoon crop which experienced dry

conditions (FSC, 2003). In fact rain came late in the first

ratoon season as the crop experienced moisture stress during

early growth stages i.e. November and December 2002. The

months of January and February 2003 received rain but was

less than the long-term (117 years) monthly mean for Rarawai

mill (FSC, 2003). The second ratoon received slightly

better rainfall than plant crop but soil erosion levels were

lower in all the treatments because soil surface had

stabilised after the initial erosion process.

The stalk height measured in plant and second ratoon showed

that rainfall was necessary for healthy plant growth in the

96

rainfed sugar industry. Hence, soil moisture is a limiting

factor that will affect plant growth and development.

5.3 Crop cycle

The cane was planted in October 2001 during the replanting

season. The Sugar Industry Master Award Regulation 3.1

states that “a grower shall plant all cane to be harvested

by him during the following year’s harvesting season, by 31st

October of the year preceding the year of harvest”.

The cane that is replanted will be harvested the following

year at 11-12 months of age. Any immature cane that is

harvested and crushed has lower recoverable sugar and

affects overall sugar production. Cane planted in March and

April (normal planting season) has a longer growing period

and is harvested at 13-15 months after reaching maturity as

determined by brix level in the field. The brixing (field

estimate of sucrose content) of farms before the start of

crushing season guides the field staff in selecting the

sweetest cane to harvest first.

Every effort was made to ensure that plant and two ratoon

crops were harvested at 12 months of age.

97

5.4 Treatments – Planting strategy associated with

conservation practice

Treatment 1

Sugarcane was planted across slope to slow downward movement

of water and soil as practised widely in the cane belt

areas. In plant crop furrows were taken out across slope

without any conservation practice.

Treatment 2

Here cane was planted uphill and downhill for comparison

with other planting strategies where furrows were taken out

across slope. Such practice is strictly prohibited on hill

slopes. It proved to be the least desired method of

planting cane on slopes which resulted in greater soil loss

and lower cane yield (tonnes cane per hectare) with

increasing period of cultivation.

Treatment 3

The vetiver hedgerow acted as barrier against surface runoff

and soil erosion. Introduction of machinery in the farming

system have seen demise of vetiver hedge which is seen to

cause a hindrance to farming operations. Animals are able

to move around an overgrown hedge and terrace, whereas

harvesting machinery cannot. The cane lorries that remove

harvested cane from steep slopes are not able to pass

through the hedges nor over the terrace. Thus vetiver is

98

ploughed out to plant an extra row of cane to increase cane

production.

Treatment 4

The trash cover provides very cost effective measure to

control soil erosion on hill slopes. Trash not only

controls weeds but retains moisture in the soil profile for

plants to grow well. On the other hand trash is burnt

because of fear that young ratoons will be destroyed during

fire.

5.5 Crop growth parameters

5.5.1 Germination

Overall germination in the trial was low (below 71 %).

Single eye-setts were cut from whole stalk cane. Those with

good eye buds were selected and planted in small plastic

bags (5” x 8”) filled with top soil. The setts were

regularly watered and fertilized for good establishment of

shoot and root system.

These potted plants were then transplanted in the gaps to

achieve uniform plant population in each plot.

99

The potted plants transplanted in the field gave reasonable

yield in terms of tonnes of cane per hectare for plant and

ratoon crops.

5.5.2 Tillers

The number of millable stalks decreased in second ratoon

compared to plant crop. To some extent this may explain for

reduction in cane and sugar yield as found in Naidiri

variety. Such agronomic characteristic would be seen as a

cultivar with poor ratooning ability by growers since

ratoons are kept for a longer period of time in Fiji.

Based on the profit margin realised from an existing crop

the grower then decides whether to replant or continue to

cultivate the ratoon.

5.5.3 Stalk population

In the early growth stages of plant crop stalk population

was higher than ratoon crop as expected. A sharp decline in

stalk population was observed in the rapid growth stage from

January to May with highest reduction in the treatment where

cane was planted uphill and downhill for plant and ratoon

crop respectively. The treatment which had cane planted

across slope with trash mulch had least reduction in terms

of stalk number due to conditions suitable for healthier

growth.

100

5.5.4 Stalk length

Based on periodic stalk height measurement cane stalks were

shorter in ratoon than in plant crop. The growth may have

been affected due to erosion of top soil, decrease in

organic matter and low water retention with increasing

period of cultivation on a sloping land.

In second ratoon, treatment which had cane planted across

slope with trash mulch produced 50-100 mm longer cane stalks

than other three treatments investigated in the study but

none were different from each other at 5 % level of

significance.

5.6 Cane and sucrose yield

Implementing correct cultural practice under rainfed

condition would reduce runoff therefore increase

availability of water in the root zone for nutrient uptake

and crop growth. The reduction in cane and sugar yield was

not significant (P>0.05) in first and second ratoon crop but

is likely to further decline with increasing period of

cultivation on a sloping cane farm. Such was the trend

during the last two years except for Treatment 4 where cane

yield was greater than 80 tcha-1 over the two years. Poor

farm management practices will substantially affect farm

income and erode the confidence of the grower to invest on

101

the farm. It is evident that if the present trend continues

and under new price arrangement which is to come into effect

from 2007 season, growers’ that practise zero conservation

would become unproductive due to high cost of production.

This will have a huge bearing on the overall crop size and

the future of Fiji sugar industry.

Similar observations have been made at sites in the Seaqaqa

area by Morrison et al. (2005) where two fields located on

rolling terrain, on almost identical soils, separated only

by a narrow road, had major differences in the management

practices, with SQ4 being managed well (trash retention

unless burnt accidentally, application of recommended rates

of fertilizer, and good crop management techniques) and SQ5

relatively poorly managed. Such was the case that from 1988

to 1993, SQ5 had to be “retired” from cane farming, as the

farmer was unable to produce an economic return from this

farm.

In relation to above, a harvesting gang needs to take into

consideration harvesting of farms located on undulating or

hilly land. Since some of these farms are harvested late in

the season (beginning of wet season) the surface area is

exposed to direct impact of raindrops, resulting in soil

erosion. This is compounded by indiscriminate burning in

order to jump the queue and expedite the harvesting process.

Therefore the gang committee needs to carefully draw up the

102

harvesting program which is to be incorporated in the

Memorandum of Gang Agreement (MOGA) that allows bulk of this

cane to be harvested before rain sets in October. This will

bind the gang and guide field staff (FSC) in relation to

harvesting of individual farms. Burning not only

accelerates erosion but causes great difficulty in

harvesting and haul-outs by means of tractor/trailer and

lorry mode during wet period. The chain effect is such that

the miller also suffers due to the inconsistent supply of

cane to mills, decline in sucrose content, increase in

tonnes cane tonnes sugar (tcts) ratio, extended season

length and over expenditure which has a direct bearing on

the price ($) for a tonne of cane.

5.7 Runoff and soil loss

The results of plant and first ratoon crop show that surface

runoff was related to rainfall as established from different

management practices used (Refer to section 3.9). The

rainfall: runoff ratios are given in Tables 4.8 and 4.11.

In both the years, Treatment 2 had the highest calculated

ratio and the least being Treatment 4 where trash cover in

the first ratoon crop retarded water flowing down slope thus

allowing water to soak into the soil. As illustrated

graphically in Figures 4.9 and 4.11 runoff volume was high

during initial growth stages i.e. before establishment of

leaf canopy which acts as cushion against raindrops falling

103

on the soil surface. Brakensiek and Rawls (1982) reported

that surface runoff was directly related to rainfall,

infiltration, surface storage, and plant interception.

Infiltration depends on soil texture, soil surface

condition, soil porosity, and antecedent soil moisture

(Rawls et al. 1982). The soil at the trial site was

described as sandy clay loam since it contained 48 % sand,

21 % silt and 31 % clay. Such characteristic may have

increased the infiltration as it tends to be greater in

sandy soils than in clay soils. However, surface runoff

increases due to reduced infiltration resulting from surface

sealing. With rough surface conditions or good crop stand,

all rain can be stored from small rain events, resulting in

no runoff or erosion as observed during later stages of

growth period.

As far as soil loss was concerned during the study period,

it was reduced by canopy formation and ground cover which in

this case was cane tops left behind after harvesting

successive crops. This was particularly true for the

treatment where cane was planted across slope with trash

mulch (T 4). In second ratoon, treatment which had cane

planted across slope but without trash cover (T 1) had

maximum (2498 kgha-1yr-1) soil loss caused by water retention

in the sub-surface layer as explained in section 4.4.3. The

field capacity increased quickly from rainstorms causing

increased runoff and erosion.

104

As described by researchers elsewhere, the susceptibility of

soil to erosion can be reduced over time by improved soil

management (Foster et al. 1985). These practices include

incorporation of crop residue and manure to build up the

soil’s organic matter.

Planting on contours, terraces, strip-cropping, and grassed

waterways are structural conservation practices that support

cultural practices such as conservation tillage. The

effectiveness of these support practices results primarily

from control of runoff. For example, contouring causes

runoff to flow along a much reduced grade than when it flows

directly downhill. Terraces shorten slope length, which

reduces runoff rate. Terraces and grassed waterways both

dispose of runoff from fields at nonerosive velocities, thus

preventing concentrated flow erosion (Foster et al. 1985).

105

On-site effects

Short-term

Long-term

Damage to young plants Loss of water & fertilizer

Decrease in top soil quality Exposure of sub-soil

^uprooting

^runoff

^decrease in rooting depth ^increase in clay

^washing away

^sediments

^reduction in soil OM

^change in texture

^decrease in soil pH

^decrease in soil

aggregate stability

Figure 5.1: Effects of soil erosion.

106

5.8 Soil conservation constraints and implications

In-spite of the clearly demonstrated usefulness of trash

mulch and vetiver hedges the growers are very reluctant to

retain trash and likewise establish new vetiver hedges. In

many cases the trash is burnt because of fear that young

ratoons will be destroyed as a result of fire whereas

established vetiver hedges have been removed to plant an

extra row of cane to increase cane production.

There are several constraints in managing effective soil

conservation controls. The major ones are discussed

hereunder.

5.8.1 Land tenure legislation

Land tenure is a major issue not only politically but also

from a land management point of view. Under the existing

Agricultural Landlord Tenant Act (ALTA) the grower is given

a lease by Native Land Trust Board (NLTB-lessor) for a

period of 30 years. A large number of the leases have

expired between 1997 and 2004 and the remaining will follow

suite. As a result for the tenant growers there is

substantial anxiety regarding the renewal of the lease.

Will it be renewed and for how long on what terms and

conditions? The lack of long-term security of tenure to

tenant farmers (lessee) is often blamed for lack of

107

conservation practices in cane fields. Other factors are

also involved such as growers like “clean” fields so burn

the trash rather than using it for mulch. Hence, there is

real danger of further decline in cane production in the

future.

It is worth highlighting that high rates of erosion are

occurring despite the fact that there is adequate

legislation to prevent bad land husbandry. For example the

instruments of title governing agricultural leases include

the following clauses to prevent land degradation:

(i) “To farm and manage the land in such a way as to

preserve its fertility and keep it in good

condition.”

(ii) “Not to clear, burn off or cultivate any hillside

having a slope more than twenty five degrees from

the horizontal or the top twenty percent (measured

vertically) of any hills having such slopes.”

(iii)“To regularly manure the land.”

5.8.2 Extension service

The removal of farm advisors in the recent past has

aggravated the situation that already existed. The lack of

consultation with other stakeholders also had a major impact

on the husbandry practices and overall crop size. However,

108

work has commenced to revive the services once provided to

growers but under a different arrangement, if implemented.

There has been little support to assist growers in solving

problems related to the vetiver hedges. The main concern of

the grower is loss of productive land, hindrance to farm

machinery operations and the harbouring of pests. The

extension efforts have also been negligible in the area of

soil conservation. These can be resolved by an effective

hedge maintenance program through the extension services.

5.8.3 Economic implications of erosion

A major economic implication is the declining productivity

of sugarcane in marginal areas. The growers place the blame

of low productivity on sugarcane varieties and the quality

of fertilizers imported. However, a more likely reason is

the impact of soil erosion on the productive capacity of the

soil. The growers suffer from erosion induced production

losses. The yields and ratooning ability in these areas

have been declining rapidly.

The damage from induced erosion is also serious. Flooding

in low lying areas and sedimentation downstream affects

mangrove forest and coral reefs that threatens our marine

life.

109

It is also obvious that a dry spell appears to be a major

drought mainly due to the fact that the top-soil on steep

lands has been washed away, where no soil conservation

measure has been adopted. As the soil profile narrows, the

apparent drought effect spreads down-slope and appears more

intense with much lower yields.

110

Chapter 6

CONCLUSION and RECOMMENDATIONS

An investigation was conducted to compare different planting

strategies associated with best management practice at

Navoli, Veisaru, Ba on a sloping cane farm. The study

provides qualitative as well as quantitative data to Fiji

Sugar Corporation to map out way forward in terms of “best

farming practices” on hilly terrains.

The results of the plant crop showed significant (P<0.05)

difference in cane and sugar yield. This was probably due

to increased length of planting in the uphill and downhill

plot rather than management practices used. In ratoons

differences did not reach significant level but higher (>80

tcha-1) yields were achieved in plots where trash was

retained and cane planted across the slope (T 4) compared

with other three treatments with no trash (T 1-cane planted

across slope, T 2-cane planted uphill and downhill, T 3-cane

planted across slope with vetiver hedgerow).

The results show that grower would earn additional income of

F$150-$400 and F$700-$1000 in the first and second ratoon

crop respectively by keeping trash on the ground. Such

111

practice is likely to increase organic content of soil and

water retention in the root zone for healthy growth, reduce

surface runoff and soil erosion, and sustain soil

productivity for a longer period of time especially in the

monoculture farming system.

The results indicate that soil loss was largely affected due

to different planting strategies associated with

conservation practice. It appears that the trash acted as a

protective layer under high intensity rain and thus

resulting in only 153 and 221 kgha-1yr-1 soil eroded in first

and second ratoon crop respectively. Where cane was planted

uphill and downhill the soil loss was maximum resulting in

16 376, 259 and 2274 kgha-1yr-1, in plant and two succeeding

ratoon crops respectively. The very low soil loss in the

first ratoon crop was attributed to almost drought

conditions prevailing during the year. The annual rainfall

for study period was 2140, 1007 and 2351 mm for plant and

ratoon crops being 92, 43 and 102 % of the 117 years long-

term mean.

The results show that under rainfed agriculture in Fiji the

most effective and practical way for water and soil

conservation on a sloping cane farm is to plant cane across

the slope and conserve trash. The practice can be adopted

with very low cost due to the fact that no cultivation is

required.

112

The results indicate that erosion of top soil produced some

marked changes in the top soil properties at the trial site.

Many of the changes could be related to decrease in organic

matter contents and soil pH with increasing period of

cultivation. It is reasonable to suppose that decreased

sugarcane yields will be encountered accompanying the

decrease in organic matter and associated decrease in

exchangeable bases. Hence every effort must be made to

ensure that further decline in soil quality does not occur

following the changes that result from initial land

preparation and cultivation on sloping farms.

The growth measurement summary clearly indicated that

rainfall during active growth period from November to May

was essential for cane growth in Fiji. For example, the

most rapid stalk elongation period for plant crop occurred

when crop was four to five months of age as it coincided

with high rainfall and high maximum and minimum temperature.

The average elongation rate during this period was 19 mm/day

compared to 9 mm/day two months later which is considered to

be the drying off period when low rainfall and cooler night

temperature after April affect vegetative growth of

sugarcane plants.

The results indicate that tiller number, stalk population

and stalk length were not affected by different planting

strategies associated with conservation practice. However,

113

a notable change was observed in the second ratoon crop as

the number of tillers during the early growth stage

decreased from six to two millable cane stalks prior to

harvest. Such agronomic characteristic of Naidiri variety

will be of concern to growers’ because the number of

millable stalks determines the final cane yield per unit

area.

In terms of plant breeding research, it is a challenge for

breeders to improve their line of crosses for better cane

yielding varieties. Since Mana is the dominant variety in

the Fiji sugar industry it becomes a challenge rather than a

difficult task to motivate growers to plant other high

yielding cultivars.

There is urgent need to revive extension services to growers

after lapse of four years. Extension is the link between

growers and research and vice versa in order to improve

productivity at farm level as determined by the Sugar

Technical Mission of India in their report to Fiji

government in 2005.

All effort shall be made in conjunction with field and

extension staff to educate growers to conserve trash on hill

slopes and harvest fields prone to soil erosion before the

wet season.

114

Similarly growers shall be assisted to plant vetiver

technology to reduce soil erosion on undulating to hilly

lands. It is also necessary to provide training to new

incoming growers (entering sugar industry for the first

time) and existing growers to increase awareness.

Educated growers are an asset to the Fiji sugar industry.

115

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125

APPENDICES

Appendix 1

1A. % POCS Calculations from Polarimeter Recordings

a. % Cane Sugar in juice = (Pol reading) x 26.00

99.718 x App sp gravity 20/200C

where – 26.00 g is the normal weight when the

polarimeter used is fitted with the international

scale.

- 99.718 x app. sp gravity 20/200C is equal

to the weight in grams of 100 ml solution.

* Apparent specific gravity 20/200C is obtained from

table 16 in “Cane Sugar Hanbook” (Meade and Chen,

1977).

* “Pol reading” is the reading obtained from

polarimeter.

126

b. % Cane sugar in cane =

% cane sugar in juice x 100-(%Fibre+5)

100

c. % Soluble solids in cane =

Brix of juice x 100-(%Fibre+3)

100

d. % Impurities in cane =

(% Soluble solids in cane) – (% Cane sugar in

cane)

e. % POCS = % Cane sugar in cane – ½ (% Impurities in

cane)

f. Purity = % Cane sugar in cane = Pol % Brix

% Soluble solids in cane

Reference:

Raw Sugar Payment Analysis: Analytical and Measurement

specifications, CSR Limited NSW.

127

1B. Determination of Polarimeter Readings

a. To a bottle of cane juice extracted from the macerated

fibre, powdered dry subacetate of lead was added for

clarification. The amount added must be the minimum for

clarification as overloading will induce errors.

Approximately 0.6 g per 100 ml extract is usually

sufficient.

b. Vigorously stir the extract plus lead acetate for five

seconds and then allow to stand for 30 seconds to permit

flocculation of the precipitate.

c. Place filter paper, Advantec No. 106, in a filter

funnel.

d. Now place the filter funnel in the mouth of a 125 ml

conical flask.

e. Pour the leaded extract, in one operation, into the

filter funnel taking care not to overflow the upper edge

of the filter paper.

f. Rinse flask with the first 10 ml of the filtrate and

discard. Collect clarified filtrate for pol reading.

128

g. Before polarizing check the clarity of the filtrate. If

the filtrate shows any sign of haziness, add a few drops

of acetic acid to clear.

h. Cool the filtrate to room temperature 200C. At least 50

ml of filtrate is required to adequately rinse and fill

the polarimeter tube.

i. Pour all the filtrate into the funnel feeding the

polarimeter tube.

j. Record the reading obtained, in the computer input form

for processing.

129

Appendix 2

2A. Summary of soil loss and runoff data for plant crop.

The means are average of four replicates.

SOIL LOSS (kg/ha) RUNOFF (L/ha) No. DATE T1 T2 T3 T4 T1 T2 T3 T4 1 06.12.01 171 176 181 134 8829 8794 10615 85462 15.12.01 1437 2060 827 992 153237 190136 170833 139668

Dec 1608 2236 1008 1126 162066 198930 181448 1482143 08.01.02 401 423 292 246 44674 57001 41592 339164 16.01.02 850 1414 724 781 1308918 1736151 1406284 9661625 25.01.02 609 943 458 545 102744 195091 104628 559866 30.01.02 508 806 353 370 105333 195834 104757 73970

Jan 2368 3586 1827 1942 1561669 2184077 1657261 11300347 05.02.02 721 1065 508 667 172585 246674 192766 1366008 07.02.02 249 509 154 130 26211 46134 23367 161629 11.02.02 896 1063 528 675 201767 312555 228690 17829510 13.02.02 15 30 11 28 2380 2631 1980 212011 14.02.02 583 890 412 481 115764 173725 123740 9973212 18.02.02 428 776 264 206 61089 99209 58071 4292713 21.02.02 482 906 371 329 70324 107633 73129 5801614 25.02.02 482 919 411 846 494789 865595 559998 42539715 26.02.02 91 435 122 215 42695 106280 76324 58654

Feb 3947 6593 2781 3577 1187604 1960436 1338065 101790316 04.03.02 223 889 225 410 150251 276624 216458 17411517 11.03.02 383 795 477 1424 522826 733749 619404 67517318 13.03.02 200 184 93 285 178793 207217 151866 130936

Mar 806 1868 795 2119 851870 1217590 987728 98022419 02.04.02 250 384 167 198 73536 128873 69960 7760520 08.04.02 105 227 39 66 39016 73902 27474 3253221 11.04.02 337 420 161 261 156509 230436 128746 14752122 16.04.02 148 299 62 139 54197 105332 40969 55700

Apr 840 1330 429 664 323258 538543 267149 31335823 07.05.02 279 405 117 130 143958 251720 88561 8813724 21.05.02 110 146 53 56 60724 107917 37573 40067

May 389 551 170 186 204682 359637 126134 12820425 01.07.02 58 104 22 40 127719 220430 78732 7115626 02.07.02 35 46 9 19 15100 30056 8690 11420

Jul 93 150 31 59 142819 250486 87422 8257627 09.08.02 50 62 24 26 50876 64199 24602 29779

Aug 50 62 24 26 50876 64199 24602 29779Total kg/ha 10101 16376 7065 9699 L/ha 4484844 6773898 4669809 3830292

t/ha 10.1 16.4 7.1 9.7 m3/ha 4485 6774 4670 3830

130

2B. Summary of soil loss and runoff data for first ratoon

crop. The means are average of four replicates.

SOIL LOSS (kg/ha) RUNOFF (L/ha)

No. DATE T1 T2 T3 T4 T1 T2 T3 T4

1 24.01.03 23 8 12 6 216429 188190 158463 141920

2 29.01.03 5 2 2 2 5942 6208 4563 4731

Jan 28 11 14 7 222371 194398 163026 146651

3 11.02.03 4 3 2 5 25969 23048 19979 19867

4 24.02.03 21 15 32 7 42260 43466 34841 20675

Feb 26 18 35 12 68451 66514 54820 40542

5 03.03.03 20 6 12 2 51039 54534 41788 25710

6 10.03.03 22 10 11 3 13759 12847 6680 10271

7 11.03.03 8 5 15 2 29813 41289 19631 9717

8 12.03.03 13 13 17 4 130279 208327 153376 36147

9 13.03.03 6 6 3 3 140039 227222 143993 43408

10 14.03.03 80 33 18 6 48601 73918 47068 16494

11 17.03.03 5 4 2 2 59164 79217 66890 18212

Mar 152 76 78 23 472762 697354 479426 159959

12 11.04.03 6 10 5 5 123493 142684 108745 36180

13 28.04.03 32 56 12 12 53696 47658 33553 34642

Apr 38 66 17 17 177662 190342 142298 70822

14 19.05.03 130 89 104 94 25285 21558 11131 16251

May 130 89 104 94 25463 21558 11131 16251

Total kg/ha 375 259 248 153 L/ha 966709 1170166 850701 434225

t/ha 0.37 0.26 0.25 0.15 m3/ha 967 1170 851 434

131

Appendix 3

3A. Soil chemical data after harvest of plant (P) crop at

Navoli, Veisaru, Ba. These means are of four

replicates.

Exchangeable bases (mg/kg)

Treatment#

pH(H2O)

Mod.Troug P (mg/kg) K Ca Mg

1234

5.75.65.65.5

286246196140

173184243261

2623268426852692

747779742764

LSD 5 % CV %

NS2

NS62

NS30

NS13

NS12

132

3B. Soil chemical data after harvest of first (R) ratoon

crop at Navoli, Veisaru, Ba. These means are of four

replicates.


Treatment#

pH(H2O)

OM%

Mod.Troug P(mg/kg) K Ca Mg

1234

5.65.55.65.8

2.02.12.22.0

242225209171

317241290290

2763279331072852

624618646625

LSD 5 % CV %

NS6

NS16

NS57

NS33

NS17

NS13

133

3C. Soil chemical data after harvest of second (S) ratoon

crop at Navoli, Veisaru, Ba.


Treatment#

pH(H2O)

OM%

Mod.Troug P(mg/kg) K Ca Mg

1234

5.05.35.15.5

2.11.92.42.0

250257104125

312214291368

2329245325112546

556609625623

LSD 5 % CV %

NS7

NS21

NS64

NS40

NS18

NS16

134

Appendix 4

4A. PEDON NAVOLI

Location : Navoli, in Veisaru sector, Ba

Physiography : SSW concave facing; slope 9-100

Topography : Rolling

Drainage : Site and profile well drained

Vegetation : Sugarcane and talasiga vegetation

Parent material : Volcanic

Climate : Average annual temperature 260C,rainfall 2300 mm annually with marked dry season June-November

Profile description (by R.J. Morrison, J.S. Gawander and A.N. Ram)

Ap1 0-12 cm : sub-angular blocky; moderately developed structure; course, medium and fine roots; ants; contains weakly weathered andesitic material; stones and gravel possible from road material; silty clay; boundary is relatively straight.

Ap2 12-32 cm : variable from 20 to 32 cm; dark brown; weakly developed sub-angular blocky; fine granular; very compact (plough pan); firm to friable; coarse stones and gravel; few fine roots; clay; some ant activity; over 1/3 there is distinct wavy boundary.

Bw 32-74 cm : covering 1/3 of the pit; stones from road material; sub-angular to blocky; few fine roots.

C 74-150 cm : varying color (red, yellow, orange, black) in situ volcanic; massive breaking to angular blocky; no structure, few fine roots

135

4B. Pit dug at the trial site at Navoli, Veisaru, Ba to

study soil profile.

Ap1 0-12 cm

Ap2 12-32 cm

Bw 32-74 cm

C 74-150 cm

very compact (plough pan)

Graphical illustration of the above

136

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