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5. LAND PREPARATION, SOIL CONSERVATION AND FIELD
ESTABLISHMENT
5.1. Land preparation
It is important to employ appropriate clearing methods to remove existing stand.
Use of monkey grubber to pull out existing trees with all the roots is important.
If the old stand is rubber, proper sanitary measures should be taken to avoid the
spread of white root disease in young clearings. Procedure adopted in uprooting
old rubber stands infested with white root disease can be summarized as follows:
-
Demarcation of all white root patches encompassing 3 - 4 healthy looking
rows of trees in the old stand.
-
Use of naturally occurring rocks (permanent) to demarcate the white root
patches.
-
If naturally occurring rocks are absent bury large rocks in the soil to
demarcate white root patches.
-
Paint rocks with lime and salt mixture for easy identification.
-
Excavate and remove as much as infected roots as possible especially
from the edges of the patch (active fungus or the inoculum is at the edge
of the patch).
-
Centre of the patch is relatively free from the inoculum. Therefore it is
not necessary to excavate the middle or centre.
-
Collect all the roots up to pencil thickness from within the patch and
burn in situ.
-
Never roll infected stumps from the white root patches down the slope or
never try to transport them to any other area.
-
When uprooting, do not cut large lateral roots to facilitate uprooting.
-
Change planting points and inter row distance between replanting cycles.
-
Establish a dense creeping leguminous cover such as Pureria phaseoloides.
-
Start clearing shortly after S.W. Monsoon of the previous year so that
burning can be done in dry season (February) before the next main
planting season (May – June next year) in wet zone.
5.2. Lining and holing
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Lining is done on contours.
Holing should be done in April of the same year of planting.
Hole size: 60 x 60 cm and 75 cm deep.
5.3. Planting Distance:
Recommended spacing gives stand of 500 trees/ha.
Square planting: 4.3 x 4.5 cm.
Avenue planting: 3.5 x 5.5 m and
2.5 x 7.75m (for intercropping).
Holes should be filled with top soil few weeks before planting.
If polybag plants are used holes should be filled only partly.
Basal mixture: should be mixed with top 15 – 20 cm of soil 2 – 3 weeks before
planting if the planting material is bareroot budded stumps.
For polybag plants basal mixture is not necessary.
5.4. Soil conservation
Erosion can be described as removal of soil by force of water and wind
Soil conservation is important in rubber land because
i.
Most of the rubber growing areas are steep and
ii.
Receive high rain fall in both monsoons
Improper soil conservation can result in

Dispersion of soil aggregates. This is due to
i. Direct impact of rain fall.
ii. Removal of binding substances by water.

Soil particles washed into cracks and pores of soil. This makes soil
impervious to water and increase surface run-off.

Due to exposure of clay pan infiltration and aeration capacity of the soil is
decreased.

Removal of top soil.

Differential removal of fertile top soil constituents (removal of clay particles,
organic matters leaving behind sand and stones).

Sedimentation of tanks and waterways.
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5.5. Objectives of Soil conservation
i. To improve of soil structure to make the soil more resistant to
detachment and to make soil more absorptive for surface water.
ii. To provide a surface cover to protect soil from the impact of rainfall.
iii. To slow down surface run-off.
iv. To providing safe ways to disperse excess run-off.
5.6. Methods of soil conservation
Methods can be categorized under three main headings:
1. Agricultural
2. Biological
3. Mechanical
5.6.1. Agricultural methods
a)
Land preparation:
should be completed before monsoon.
b)
Contour planting:
should be adopted specially on steep or undulating land.
c)
Embankment and fences:
Should not be clean weeded to expose the soil.
Weeds must be kept under control by slashing.
5.6.2. Biological
Ground covers
Soon after clearing the land, establish a recommended cover crop.
In wet zone, this can be done in March with regular showers.
Vetiver grass
Grow on contours as a dense hedge.
Helps to reduce erosion and conserve moisture.
Vetiver grass conserves soil by
i.
Binding the soil along the contour by its deep, strong
and dense root system.
ii.
Slowing the run-off of water and filtering out the soil
carried by water.
iii.
Forms natural terraces.
iv.
Provides a good mulch due to death and decay of
leaves.
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Advantages
i. Cheap.
ii. No additional maintenance for many years.
iii. Easy establishment without disturbing soil.
Mulching
It prevents runoff and soil erosion.
Mulching provides quick surface cover when compared to live
covers which take time (6-12 months).
5.6.3. Mechanical
i. Drains:
Main drains:
Natural drains already in the land must be used.
Correct positioning of drains in the field is more important
than the distance.
Main drain can be improved by constructing reverse slope
pits, spill platforms and splash cushions with stones and
pebbles (Fig.5.1).
Fig.5.1. A main drain with spill platforms and splash cushions.
(Source: Handbook of rubber Vol. I pub. By RRISL).
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Lateral drains
Should be cut on contours.
Approximate slope is1 in 120.
Consists of series of silt pits, 3 m long 60 cm wide and 45 cm deep,
spaced at 90 cm intervals connected by shallow drains (Fig.5.2).
Fig. 5.2. A lateral drain with silt pits and bunds.
(Source: Handbook of rubber Vol. I pub. By RRISL).
Spacing of lateral drains depends on the gradients of the land.
- spaced 21.5 m for gradients of 1 in 20.
- spaced 14.5 m for gradients 1 in 20 and 1 in 4.
- spaced 7 m for gradients over I in 4.
ii. Stone terraces (Fig. 5.3)
In rocky lands lateral drains are impossible. In such areas level
contour stone terraces partially meet soil conservation needs.
Distance depends on slope. Same spacing as for lateral drains’
Upper side of the terrace should be on perfect contour.
Base should be broader than the top.
Lower side should slope towards hill side.
Base should be built with large even stones.
Stones should be laid with a reverse slope to that of land. To achieve
this, beds should be cut into the hill side.
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Fig. 5.3. Dimensions for stone terraces
(Source: Handbook of rubber Vol. I pub. By RRISL).
5.7. Field establishment and tree management
Land preparation, lining, planting distances, holing and filling have been described
under land preparation and soil conservation.
5.7.1. Planting seasons
Field planting of rubber is under taken with the onset of monsoon rains.
Rubber plantations in wet zone (South-West region of Sri Lanka) receive rain from
both monsoons. The main planting season in South-west is May- June period which
is the S.W. monsoon period. This region receives certain amount of rains during
N.E. monsoon (Oct.- Nov.) also. Planting and also infilling of vacancies can be
undertaken during this period.
In dry areas such as Moneragala, Bibile and Matale, the only planting season is N.E
monsoon (from October – November period).
5.7.2. Field establishment
a. Bare-root budded stumps
Bare-root brown budded stumps can be planted in both wet and dry areas. But
bare-root green budded stumps should not be planted in dry areas.
Taproot should not be cut if it can be avoided.
Lateral roots are pruned leaving 15cm from the taproot.
Part of the filled soil should be removed from the hole (Fig. 5.4a ).
If the tap root is long, make a hole (15cm deep) in the centre of the planting hole,
using a crow-bar or an crowbar, to accommodate the taproot (Fig. 5.4a ).
Laterals are arranged so that they are spread around the hole (Fig. 5.4a).
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Fig. 5.4a. Correct positioning of the bare root budded stump in the planting hole
When the budded stump is placed in the hole the bud patch should be about 5cm
below the ground level, facing North East direction.
Pack the soil around the tap root using the crow-bar by plunging it around the
budded stump and pressing the soil towards the tap root (Fig. 5.4b).
Fig.5.4c
Fig. 5.4b
Fig. 5.4. Stages of planting a bare root budded stump.
(Source: Handbook of rubber Vol. I pub. By RRISL).
After filling the remaining part of the hole, the soil around stump is packed by
treading the soil around the stump without damaging laterals.
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Leave a space of 5cm between the level of the packed soil in the hole and the
ground level (Fig. 5.4c). This will avoid the condition known as “elephant foot” in
old clearings which is the exposure of the bud union above the ground surface.
Cut a drain to drain off excess water that might collect around the stump (Fig. 18f).
b. Planting polybag plants in the field
Technique is same for any type of polybag rubber plant (green or brown budded
polybag plant, young budded plant etc.).
Only plants with hardened top whorl should be transplanted in the field.
Number of plants with hardened leaves can be increased by discontinuing
manuring about 2 months before planting.
If taproot has penetrated into the ground, tilt the bag to a side carefully and cut the
taproot with a pair of secateurs or sharp knife. This should be done only on plants
with hardened top leaves
Water the plants till field transplanting. But avoid over watering which will lead to
loose soil in the bag at transplanting. This condition will lead to increased casualties
in the field due to disturbed root system.
Transport to the field with great care without disturbing soil in the bag.
Before planting check the depth of the half-filled hole and adjust it either by filling
or removing soil so that the bud union is about 5cm below the ground level.
Polybag plants can also be deep planted so that the bud union is about 15 to 20 cm
below the ground level. This is done to avoid the effect of the rootstock on yield
when the tapping cut comes close to the bud union.
Before placing the polybag plant in the hole remove the base of the polybag using a
sharp blade or knife (Fig.5. 5a & 5.5b) and then position the bag in the hole, slit the
bag half way along the length, starting from the bottom (Fig. 5.5c)
While filling the hole, cut through the remaining half and remove the polythene
bag carefully without disturbing the soil (Fig. 5.5d).
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Fig. 5.5a
Fig. 5.5c
Fig. 5.5b
Fig. 5.5d
Fig. 5.5. Stages of planting polybag plants in the field.
(Source: Handbook of rubber Vol. I pub. By RRISL).
5.7.3. Tree management
a. Growth of scion
In an event of an unexpected drought, regular watering should be done.
Regular removal of stock shoot should be done.
Allow only one shoot from the scion bud.
Scion should be made to grow without branching up to a height of 2 to 2.5m
b. Stand
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Maintain a stand of 500 trees per hectare.
To achieve this, filling the vacancies created due to death of plants is a must.
To have a stand of uniform growth, it is very essential to replace weak plants with
vigorous plants. Uniform growth of plant ensures that majority of tees which come
to tappabale girth more or less at the same time. This will enabling tappers to finish
the tapping task as they don’t have to walk a long distance from one tapping tree to
the next for tapping.
Filling vacancies and replacement of weak plant can be done in the N.E. monsoon
(in the same year of planting) or in the S.W. monsoon (in the 2nd year of planting) in
wet areas .
In dry areas vacancy filling is done in N.E monsoon in the next year.
For infilling etc., about 10% of the plants of the total number planted in the field is
kept as polybag plant or trenched plants.
Trenched plants: Bare-root stumps planted in trenches and allowed to grow for
about one year.
5.7.4. Branch induction
This may be necessary in some clones such as RRIC 121. If main stem does not
branch after about two years (when the main stem is 2 to 2.5m in height), induction
of lateral branches is recommended. Two methods are available.
a. Leaf folding method
Terminal leaf whorl should be hardened. In this method few terminal leaves are
bent up and brought together covering the apical bud. Folded leaves can be kept
together with a help of a rubber band (Fig. 5.6a).
Fig.5.6a. Leaf fold method
Fig.5.6b. Leaf cap method
Fig. 5.6. Branch induction. (Source: Handbook of rubber Vol. I pub. By RRISL).
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b. Leaf cap method
This can be adopted when the terminal bud is about to break or when young
leaflets have just unfolded.
Make a cap with detached matured leaves, place it over the apex of the stem and
fastened with a rubber band (Fig. 5.6b).
In both methods the cap should be removed after 3 to 4 weeks.
5.7.5 Growth
It is important to maintain a vigorous growth of young rubber clearings. This very
much depends on aftercare practices such as manuring , weed control and pest and
disease control etc.
Growth is usually measured as the increase in girth of the trunk (stem) at a height
of 120cm from the bud union.
Annual growth potential of new clones is about 10cm and plants are expected to
reach 50cm in girth at 120cm in the 5th year after planting.
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6. COVER CROPS, MULCHING AND WEED MANAGEMENT
6.1 Cover crops
Establishment and management of cover crops are important aspects of rubber
cultivation because of high monsoonal rains and steep terrain in rubber growing
areas.
Legumes are preferred as cover crops because of their ability to fix atmospheric
nitrogen.
Advantages:
i.
ii.
Soil conservation
Improvement and maintenance of soil fertility
i.
Soil conservation
a.
Direct protection of soil surface from rain or blowing by
wind.
b. The root systems of the cover crops bind soil together.
c.
Prevent surface wash – due to bund formation by covers.
d. Slow down the water movement – due to creeping habit.
e.
Roots of the covers make soil porous allowing better
penetration by rain water thus reducing surface run off.
ii.
Soil fertility
Cover crops
a.
Provide a mulch due to natural death
b. Add humus due to death and decay
c.
Improves aeration by the cover crop root
d.
Provide mulching material
Qualities of cover crops:
a) Should be able to multiply easily
b) Should not compete with rubber (the main crop)
c) Rapid growth, both in full sunlight and shade to give abundant
leaf
d) Tolerance to slashing/pruning
e) Tolerance to drought and diseases
f) Should competitive with weeds
g) Should not secrete toxic products
h) Should be able to eradicate easily
i) Should not harbor pests and diseases that can attack rubber
Recommended cover crops species and their seed rates:
a. Pueraria phaseoloides
6kg of seeds/ ha
b. Desmodium ovalifolium
4kg of seeds/ ha
c. Calopogonium mucunoides
6kg of seeds/ ha
d. Centrosema pubescens
8kg of seeds/ha
e. Stylosanthus gracillis
4kg of seeds/ ha
f. Mucuna bracteata
propagated by cuttings
In high rainfall areas any species can be used.
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Stylosanthus is not recommended for low rainfall areas.
In Sri Lanka a mixture of P. phaseoloides and D. ovalifolium is commonly used.
Pueraria grows fast in early stages and covers the ground quickly. This is important
for soil conservation as young rubber plants do not have sufficient canopy to cover
the ground but cannot tolerate shade.
Desmodium shows a weak initial growth, but stand shade better. When rubber
canopy covers the ground, Pueraria will disappear and shade tolerant Demodium
will take over the function of cover crop.
Mucuna bracteata takes a long period to establish. But it provides a high biomass
and tolerates drought and suppresses weed effectively.
Seed treatment:
Some species of legumes have hard seed coat and therefore takes a log time to
germinate. To over come this problem the seeds of these species have to be treated.
Pureria, Desmodium, Calopogonium and Centrosema seeds can be advantageously
treated. Two types (acid or hot water) of treatments can be adopted.
Acid treatment: Use concentrated Sulphuric acid.
Species
Seed rate
Vol. Of acid
(ml)
Pueraria
1kg
50
Desmodium
1kg
50
Calopogonium
1kg
50
Centrosema
1kg
50
Soaking time
(mins.)
30
15-30
15-30
30
Hot water treatment:
Soaked in hot water of 600c – 800c for 24 hours. i.e. Allow the water to cool.
Establishment:
Use either seeds or cuttings depending on the species.
Puerria, Calopogonium and Centrosema – Both methods can be used.
Establish in clean weeded strips or on beds separated at regular intervals.
Can raise in nurseries and planted as baskets or balls.
As the cover grows resort to selective weeding, leaving the cover.
Manuring:
When establishing, apply 100g of rock phosphate (RP) per square meter.
In the first year dust the cover crop with rock phosphate at the rate of100 to 200kg/
ha depending on growth.
Residual effect of P applied to immature plantation persists.
Maintenance:
To avoid competition maintain a 1 to 2 m wide clean weeded strip along the rubber
rows or a clean weeded circle around the rubber trees.
6.2. Mulching
Introduction
During first 3 to 4 years after planting rubber plants do not provide adequate
protection to soil. This is due to
1. Poor canopy of the young plants and
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2. The cover crop takes 6 to 12 months to provide a cover for soil
3. In young rubber clearings in order to avoid competition from cover crops a
circle of about one meter radius around the rubber plant or a strip of about 12 m wide along the rubber rows is kept clean weeded.
Due to these reasons loss of soil, due to erosion, from rubber plantations during
first 3 years after planting is heavy. Thus soil degradation during this period is
unavoidable.
This can be avoided if mulching is adopted. Mulches provide an immediate cover
to vacant patches and the base of the young rubber plants where there are no cover
crops.
Contributions
1. Due to decaying of mulches certain amount of nutrient is added.
2. Due to decomposition of mulches certain amount of organic matter is added
to soil.
3. Prevents soil erosion.
4. Prevents loss of water from the soil surface. Thus increases soil water
retention.
5. By mulching the weed free circle around the base, growth of weeds and
cover crops in the weed free circle can be avoided.
Mulching Material
a. Paddy Straw
Rice straw has been found to be a good mulching material for young rubber plants.
Method of application
Mulch around the base of the rubber plant. Paddy straw should be spread loosely
in the weed free circle.
Frequency and time
Immediately after planting to cover the exposed soil patches of young replanting.
Mulch twice a year in March - April and August - September during paddy
harvesting period.
Rate of Application
Rate of application varies with the age.
Year of Planting
Amount per application
During first year
2 kg per application
nd
2 year
3 kg per application
3rd and 4th year
4 kg per application
th
5 year to tapping
5 kg per application
b. Tree/Bush (T/B) legumes
On large rubber plantations it is difficult to obtain sufficient rice straw for
mulching. Therefore rubber plantations will have to grow their own mulching
material.
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Recommended Tree/Bush legume species
i. Flemingia macrophylla and
ii. Crotalaria mucans (C. anagroides)
Can be grown in young rubber clearings.
Establishment
Tree/bush (T/B) legumes can be established immediately after clearing. Seeds
should be sown in a strip of land which has been weeded and forked. First row T/B
legume should be 120 cm away from the adjourning rubber row. Distance between
adjacent rows of T/B legume is 60 cm.
Manuring T/B legumes
2 kg of rock phosphate per hectare at the time of establishment and subsequently
100 to 200 kg of rock phosphate per hectare per year depending on the growth.
Lopping and mulching
1st lopping is done 4 months after planting.
3 – 4 lopping – year is possible under favorable climatic conditions.
6.3. Weed management
Weeds are considered undesirable as they decrease economic returns.
Effects of weeds
i. compete with rubber for water, light and nutrients
ii. Obstruct estate activities such as tapping
iii. Some weeds secrete growth inhibitors that suppress the growth of rubber
plants
iv. Harbors pests and diseases that can affect rubber plants
Weed management
Nature of weed management depends on the age of the clearing as follows.
i. At replanting before covers are established.
ii. In areas where cover crops have been established.
iii. Weeding rubber trees in immature areas.
iv. Weeding in mature areas.
Possible management or control methods
i. Hand weeding
ii. Mechanical control
iii. Burning
iv. Ground cover
v. Mulching
vi. Intercropping
vii. Grazing
vii. Use of weedicides (chemical control)
Choice of method depends on
i. Age of rubber plants
ii. Climate
iii. Type of weed and its distribution
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iv. Size of rubber holding
a. Hand weeding
Hand weeding is effective, expensive and bad for the soil. Hand weeding also
activates dormant seeds in the soil.
i. Along the rows (1 to 2 m wide) or
ii. Circle weeding (0.5 to 1 m radius) around the plant
b. Mechanical methods
Difficult to adopt due to terrain.
c. Burning
This is the traditional method and not recommended except when opening new
clearings. This method is destructive to soil.
d. Ground cover management
It is very effective in young rubber clearings. Cover crops are essential to preserve
soil fertility and for soil conservation.
e. Intercropping
Intercropping is another good practice to control weeds. In addition to weed
control intercropping gives an additional income. Intercropping is suitable for the
small holdings as well as large plantations.
f. Livestock grazing
Controlled grazing by livestock can keep weeds under control effectively.
g. Chemical control
Nature of the herbicide depends on the following factors.
i. Nature or type of weeds to be controlled.
ii. Objective and degree of weed control
iii. Cost of weedicides and their applications.
Most widely used weedicides in rubber plantations are,
i. Glyphosate – water soluble, kills underground parts of the weed. Effective
in controlling couch grass and illuk
ii. Paraquat (Gramoxone) is also used in rubber plantations.
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