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obtained from published or unpublished work of others and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
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....................... 45
4.3 Variation in the P 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....................... 46
xiii
4.4 Variation in the K 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....................... 47
4.5 Variation in the Ca 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....................... 48
4.6 Variation in the Mg 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....................... 49
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
4.12 Soil erosion 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....... 77
4.13 Soil erosion affected by different planting
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
4.9 Effect of different planting strategies associated
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
4.13 Effect of different planting strategies associated
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-
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.
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-
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.
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-
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.
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-
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.
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-
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.
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
respective treatments are presented in Table
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
4. Cane planted across slope
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
CV coefficient of variation
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
Cane planted across slope (T4)
SURFACE
RUNOFF
RAINFALL
MONTHS
68
Figure 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. Plotted data are the
means of four measurements.
Soil loss expressed as kgha-1yr-1
Rainfall expressed as millimetres (mm)
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 (T1)
Cane planted across slope + vetiver hedgerow
Cane planted across slope (T4)
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
T4 – cane planted across slope 3830 18 9699 9.7
Rainfall (mm) 2140
71
4.3 FIRST RATOON CROP
4.3.1 Cane and sucrose yield
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
Table 4.9: Effect of different planting strategies
associated with conservation practice in
first ratoon 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)
R R R
1. Cane planted across slope
2. Cane planted uphill and downhill
3. Cane planted across slope + vetiver hedgerow
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
tcha-1 tonnes cane per hectare
tsha-1 tonnes sugar per hectare
R first ratoon crop
NS not significant
CV coefficient of variation
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
strategies associated with conservation
practice in first ratoon 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
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
Cane planted across slope + vetiver hedgerow
SURFACE
RUNOFF
RAINFALL
MONTHS
77
Figure 4.12: Soil erosion affected by different planting
strategies associated with conservation
practice in first ratoon at Navoli, Veisaru,
Ba on a sloping cane farm. Plotted data are
the means of four measurements.
Soil loss expressed as kgha-1yr-1
Rainfall expressed as millimetres (mm)
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 + vetiver hedgerow
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
T1 – cane planted across slope 967 10 375 0.37
T2 – cane planted uphill/downhill 1170 12 259 0.26
T3 – cane planted across slope +
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
respective treatments are presented in Table
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
CV coefficient of variation
83
4.4.2 Cane and sucrose yield
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
Table 4.13: Effect of different planting strategies
associated with conservation practice in
second ratoon 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)
S S S
1. Cane planted across slope
2. Cane planted uphill and downhill
3. Cane planted across slope + vetiver hedgerow
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
tcha-1 tonnes cane per hectare
tsha-1 tonnes sugar per hectare
S second ratoon crop
NS not significant
CV coefficient of variation
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
Figure 4.13: Soil erosion affected by different planting
strategies associated with conservation
practice at Navoli, Veisaru, Ba on a sloping
cane farm. Plotted data are the means of
four measurements.
Soil loss expressed as kgha-1yr-1
Rainfall expressed as millimetres (mm)
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 + vetiver hedgerow
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
T3 – cane planted across slope +
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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Anonymous. (2002). Fiji Sugar Corporation Annual Report for
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Anonymous. (2002). FSC Sugarcane Research Centre Annual
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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.
Exchangeable bases (mg/kg)
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.
Exchangeable bases (mg/kg)
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
Appendix 5
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