The document discusses soil management practices for cashew plantations in Sri Lanka. It notes that cashew is commonly grown on various soil types ranging from coastal sands to laterite soils. Soil fertility varies widely between soils. Contour planting, contour drains, terracing, and cover crops are recommended to control erosion and increase organic matter, thereby sustaining soil productivity and cashew yields over the long term. Improper fertilizer and pesticide use can lead to pollution if not properly managed.

2. • Presently, cashew is grown mainly on Red-Yellow Latasols and
Coastal sands in the Intermediate and Dry Zones.
• To a certain extent, it is also grown on Reddish Brown Earth soils
and Red-Yellow Podsolic soils.
• The fertility status of these soils varies widely.
• The most fertile among cashew soils is the forest soils.
They are often secondary virgin soils, rich in organic
matter, on which cashew was planted with little land clearing.
Introduction

3. • The coastal sands on which cashew is often grown is poor in fertility
and yields are low unless the trees are fertilized regularly.
• The Laterite soils vary considerably in depth, texture and other
physical and chemical properties.
• Cashew is not a very common sight on water-logged or saline soils.
• Experiments conducted under the cashew research project of the Sri
Lanka Cashew Corporation showed that the young cashew plants
performed better in the deep sandy soils than clayey soils (Rodrigo
and Fernandopulle, 2002).
• It is also observed that trees grown in poor soils response well to the
application of fertilizers.

4. • It will perform better on Class I and II lands, which are not subjected
to, no or minimum land degradation than on Class IV and V lands,
which are subjected to considerable or severe land degradation, if
only we could utilize these lands for cashew.
• Since Sri Lanka still recognizes tea, rubber and coconut as the major
export-oriented plantation crops, and the scarcity of fertile soil in the
districts where the cultivation of cashew could be expanded, the soils
of less fertile could be utilized for new cashew plantations under
proper management.

5. Importance of soil management
• As cashew is also a perennial crop grown in hill country, our main objective of
any soil management program in cashew plantation should be to sustain
profitable production.
• To obtain profitable yield levels, growers must provide a favourable
environment for cashew.
• The natural characteristics of the soil along with climatic conditions,
contribute a portion of the environmental factors, and cashew growers must
take up the difference through management of inputs of various kinds.
• The soil qualities that contribute to crop productivity are extremely important
not only to high yield levels, but also to economic crop production as well.

6. • From soil productivity and soil fertility standpoint, soil conservation is essential
for long-term sustainability.
• Soil management practices that contribute to or encourage soil degradation will
reduce soil productivity and impair progress towards sustainability.
• Therefore, soil management in cashew plantations is one of the most important
management practices and need serious attention from each level of management
varying from growers, extension officers, researchers and policy makers.

7. DECREASE
by
INCREASE
by
Soil Conservation Practices
• Cover crop management
• Residue management/mulch
• Couture drains / bunds
• Terracing
• Chemical fertilizers
• Organic fertilizers
• Improvement systems to match soil,
climate, and cultivars
Soil Degradation Processes
• Soil erosion
• Nutrient runoff
• Acidification
• Compaction
• Surface Sealing and Crusting
• Organic mater loss
• Nutrient depletion by leaching / runoff
• Pollution ( by fertilizers & pesticides)
Soil productivity

8. Soil degradation
In general, the recognized forms of soil degradation are soil erosion (by water and
wind), salinization, pollution and other forms of soil physical, chemical and
biological degradation.
Physical degradation - includes soil compaction, deterioration of soil structure,
sealing and crusting of top soil.
chemical degradation - includes acidification and lowering of nutrient content and
biological degradation covers lowering of soil organic matter and reduction in soil
biological activity.
These are closely linked, loss of soil organic matter adversely affects both soil
physical properties and nutrient supply, while erosion causes loss of both organic
matter and nutrients along with soil particles.

9. Soil erosion
• Although many of the growers, consultants, and policy makers aware that erosion
decreases the productivity of the lands, they were not be overly concerned because crop
yields have substantially increased due to technological advances in crop breeding and
genetics, fertilizers and fertilizer management, pesticides and pest management, and other
agronomic technologies.
• Growers who have observed the steady increase in yield year after year regardless of
present or past erosion, have, in many cases, mistakenly assumed that erosion has not
affected productivity.
• Soil erosion is a natural process that has been occurring as long as the world has existed.
• This form of erosion which is referred to as geological erosion is a harmless process.
However, human activity often enhances the erosion process resulting long-term
mismanagement of the land and represents the greatest threat to sustained soil
productivity.

10. • Signs of soil erosion are a symptom of poor soil management and the
consequences of poor management may lead to other forms of land degradation.
• Although mismanagement of soil cause soil erosion, it can be controlled by
adopting proper soil management practices.
• The effects of soil erosion have been identified as loss of soil fertility, loss of
organic matter, deterioration of soil structure, decreased available water-holding
capacity, decreased infiltration, diminished workability, or, more frequently, a
combination of several types of damages (Buntley and Bell, 1976; Lal, 1976;
NSESPRPC, 1981).
• These effects of soil erosion often result in lower productive capacity of the soil.

11. • Some effects of the erosion are irreparable while some are repairable. Irreparable
damage to a yield-determining soil property is likely to permanently decrease the
productivity of the soil.
• Irreparable damage by erosion mainly consists of decreasing the available water-
holding capacity and the effective rooting depth which usually cannot be increased
by practical means.
• Repairable damage includes nutrient and organic matter losses, lower pH, higher
lime requirement, higher bulk density, and degraded structure.

12. • Presently cashew has been cultivated in almost all the provinces of Sri
Lanka but the majority is in gentle slopes.
• This does not mean that the erosion in gentle slopes is negligible and
the erosion control practices could be ignored.
• Therefore it is advisable to adopt appropriate erosion control
technology to minimize the repairable damages of erosion and
thereby conserve the soils of cashew plantations for sustainable
productivity.

13. Contour planting
• Contour planting is tillage and planting across the slope along the contour lines rather than up
and down hill.
• In wet zone, this method is used to reduce the soil erosion by breaking the speed of water
movement while in the dry zone, it is used to improve the moisture by reducing the runoff water
and retaining it within the soil.
• Since erosion becomes progressively more severe on long slopes, slope length has to be
controlled according to the slope gradient.
• the limits on slope gradient and length that have been established beyond which the effect is not
sufficient for erosion control (Wischmeier and Smith, 1978). It clearly indicates that land
management practices such as crop residue management or cover crop could increase the slope-
length or the distance between lateral drains. Contour ridges produced by drains form barriers that
slow the downhill movement of water.

15. Contour drains
• Contour drains which are known as diversion ditches are commonly
practiced in Sri Lanka to slower the downhill movement and divert them to
lateral drains which are constructed on the contour with a slight gradient of
slope to minimize the soil erosion within the drain.
• This would vary from 1: 120 to 1:200 depending on the steepness, soil
type and the type of ditches laid.
• These lateral drains are then connected to a leader drain at slightly
different levels.
• This would help to prevent and protect the collapse of the leader drain
and the excess water is to be carried away from the land with minimum
damage to the soil.

16. • When constructing the main drain, the natural drain lines which are already
indicated on the land should be used, except in cases where the distance
between two natural drains becomes excessive (more than 60m)
• The selecting the correct site for these main drains is more important than the
distances between them.

17. • The natural main drains can be improved by the construction of a
reverse slope pit to reduce the flow velocity and prevent scouring.
• As the leader drain carries a large volume of water, it is advisable to
pave the bottom with stone slabs.
• These will tend to reduce bank erosion while checking the rate of flow
of water down the 'drainage lines.

18. • Construction of these drains should be completed soon after land
clearing and before land preparation and prior to the heavy rains
especially if a ground cover has not been established satisfactorily.
• The tracing of the lateral drains can be done independently of the
planting rows, commencing from the middle of the two planting rows,
which are approximately on level contours

19. • The spacing of lateral drains would vary again with the type
of soil but the length of the slope (or the contour) would
be adopted with minimum effect on soil for erosion
control.
• The earth cut from the drain should be heaped up on the
upper side of the drain, in a continuous ridge.
• The cutting of drains should be started at the top of the
slope.
• This type of drains generally consists of a series of silt pits
which are connected by shallow drains on a depressed
bund of the same width.

20. • The aim of constructing these drains is that water to be absorbed
maximum to the drain and the excess water to be carried away from
each deep section to the other deep section through the shallow
section which prevents the carrying away of silt which gets deposited
in the deeper drain.
• Soil deposited in the lateral drains should be cleared regularly. This
soil can be deposited uniformly in areas above the drain.

21. Terracing (Stone terraces)
• On very rocky land, where it is impossible to cut continuous lateral drains, the soil
conservation needs are partially satisfied by the construction of level contour stone
terraces.
• These terraces can check the rate and distance of movement of surface run-off
water.
• When constructing the terrace, the base should be built with large even stones.
• The stone should be laid with a reverse slope to that of the land, to affect this,
beds should be cut into the hillside.
• For greater stability, the base of the terrace should be wider than the top.

22. • The out side of the terrace should shape towards the hill side and the upper surface of
the terrace should be above the surface of the soil.
• Thereby the eroded soil will be deposited on the upper sides of the terraces and water
will filter through the terraces.
• As in the case of lateral drains the distances between terraces should be adjusted
according to the slope of the land.

23. Compaction, sealing and crusting
• Compaction, sealing and crusting can be recognized as the in-situ processes of
physical soil degradation.
• Compaction usually occur as a result of the repeated use of heavy machinery and
trampling of animals on soils with low structural stability which tends to break the
soil structure and become aligned perpendicular to the direction of compression.
• The most common cause of sealing and crusting is clogging of soil pores by fine
grained silt and clay particles dispersed by raindrop.
• Crusting is the hardening of the surface soil as it dries up.
• All these, reduce the water infiltration which result in surface run off.
• Compaction compresses the soil mass into a smaller volume thereby reduce
porosity, increase bulk density and resistance to root penetration.

27. Nutrient depletion/ runoff
• Soil nutrient depletion is a problem facing in many cashew plantations. Since they
are noted for their hardiness often they have been neglected and hardly fertilized.
• Nutrients become depleted when their removal from the soil exceeds their
addition.
• Depletion of nutrients from the soil occurs not only by the removal of the
harvest but also through extraction by crops, leaching, erosion, volatilization and
denitrification.
• Burning of vegetation and crop residue as a pest control measure in cashew
plantations also leads to nutrient loss.

29. • Inputs include application of fertilizers and manure and atmospheric
deposition in rain. Perennial crops that are demanding of nutrients
often lead to severe nutrient depletion, sometimes to acidification.
• Nutrient depletion by leaching result in reduction in soil pH, especially
when calcium and magnesium ions which are adsorbed on to the clay
minerals are replaced by H+ ions making soil more acidic.

30. Pollution by fertilizers
• High quantities and improper methods of fertilizer application can lead
to fertilizer being leached to drainage waters, causing river and
groundwater pollution.
• Nitrogen, phosphorus and potassium are the three main nutrients that
are widely applied to soils as inorganic fertilizers.
• High amount of nitrogen fertilizer may cause toxic effects on the tender
root of cashew seedling and if leached and the contaminated water
contained more than 10ppm of NO3 would reach the toxic levels to the
humans according to the World Health Organization.
.

32. Pollution by pesticides
• The vast majority of pesticides is organic chemicals.
• They are usually used as insecticides, herbicides or fungicides in cashew
plantations.
• As most pesticide molecules are uncharged and hydrophobic, they exhibit a
stronger affinity for humus than other soil particles. However, paraquat behaves
differently and adsorbs primarily on the negatively charged surfaces of clays.
• A number of changes can happen to pesticide compounds in the soil. They can be
degraded by soil organisms or by physiochemical processes.
• adsorbed by soil organic matter, clay minerals and iron and aluminum
sesquioxides, washed into water courses through leaching and runoff, or volatilized,
resulting in atmospheric pollution.

34. Loss of organic matter (OM) from the soil
• Loss of organic matter (OM) from the soil
• Losses of organic matter in cashew plantation occur when the land is exposed to
erosion, burning of crop residue and decomposition by micro- organisms.
• Burning with low fire of crop residue or smoking is a common practice during the
new flush to control the tea mosquito bugs, which attack the flush.
• Cashew in Sri Lanka is wide spread in the dry zone where the rate of organic
matter decomposition is quite high. One of the plant nutrient problems in the Sri
Lankan cashew plantations in dry zone is, though much OM is produced, it decays
rapidly.
• Thereby the contribution of OM to improve the soil physical properties becomes
limited. However, this could be overcome by having OM incorporated into the soil
by proper management of either cover crop or green manure.

35. Benefits of soil organic matter
• Soil organic matter is the part of the soil that consists of plant and animal residues in
various stages of decay. Addition of organic matter to a soil improves its productivity. It
improves soil physical, chemical and biological properties to enhance its fertility.
a. It acts as a storehouse for nutrients such as N, P, S, and most micronutrients
b. It increases the cation exchange capacity by more than 100 fold and thereby
helps to hold nutrients already present in the soil, by keeping them from leaching
down beyond the reach of plant roots
c. It provides energy for microbial activity
d. It increases water-holding capacity as the spongy structure of humus absorbs
and retains more water
e. It improves soil structure with stable aggregates and adds stability to the soil,
against the deterioration of soil structure
f. It reduces crusting and increases infiltration of water into the soil.
g. It reduces the effects of compaction thereby increase the porosity
h. It buffers the soil against rapid changes in acidity, alkalinity, and salinity.

36. • Organic matter, an essential component of a healthy soil, is in a constant state of
transition, continually breaking down and releasing finer, more- decomposed
particles.
• Because of this process, organic matter is constantly being reduced and
therefore in constant need of replacement.
• Managing of soil organic matter should be a top priority on all cashew
plantations.
• It is more realistic to use a management system that will give sustained profitable
production without degradation of OM and productivity.

37. Management of organic matter in cashew
plantations
• Ground covers/Cover crops
For perennial crops like cashew, planted on steep slopes, continuous
ground cover is helpful in reducing erosion. It is essential to establish a
suitable ground cover after clearing and all the earthwork are completed.
If land preparation is done with south-west monsoon (Yala), regular
showers experienced during the monsoon will permit the establishment
of ground covers. These help to conserve the soil and reduce soil loss
with heavy rains in Northeast monsoon (Maha). Since the trees and the
cover crops occupy the land simultaneously, care must be taken,
particularly in young plantations, to prevent competition for water and
nutrients.

38. • The term cover crops itself describe an important function of these crops in
cashew plantations i.e.
• to cover the soil, block weeds, protect the soil surface by breaking the speed of
the erosive rain drops and also from wash by rain or blowing by wind, prevent
erosion, and maintain soil moisture, among other benefits.
• Roots of the ground cover when decayed supply organic matter and enhance the
soil structure. Therefore, the soil is kept porous and the infiltration of water is
increased while reducing the runoff.

39. Improvement of soil with cover crop
• Planting cover crops is an easy way to revitalize the soil. Cover crops
are planted in vacant space of the plantation and in the case of adult
plantations they are worked into the soil at the tail end of the
northeast monsoon well before the bearing season.
• This will enable the growers to collect the cashew nuts as the ground
is clear of heavy growth of cover crop

40. • They provide a number of advantages to the otherwise wasteful use
of space within the plantation.
• Cover crops help to retain the soil structure, lessen erosion, and
decrease the impact of precipitation on the plantation by slowing down
the runoff.
• They also reduce mineral leaching and compaction, and suppress
perennial and annual weed growth. The top growth adds organic
matter when it is tilled into the soil.
• The cover crop's root system also provides organic matter and' opens
passageways that help improve air and water movement in the soil.
• Success in the growth of cover crops requires proper selection of the
kind of cover crop, correct timing of seeding, and good management
techniques.

41. Green manure
• The primary function of green manure is to add organic matter. In general, green
manure crops in cashew plantations could be established between plant rows or
sown while they are growing and along the boundaries of the plantations.
• There are many choices of green manure crops, with a variety of benefits for
using them. The crops are divided into legumes and non-legumes. The latter
includes annual grasses, sun flower etc.
The legumes - Sunhemp (Crotalaria juncea), cluster-bean (Cyamopisis
tetragonoloba) cowpea (Vigna sinensis) Gliricidia (Gliricidia sepium) etc.

42. • provide the benefit of fixing nitrogen, actually taking nitrogen from the air and
holding it as nodules on plant roots.
• As plants are turned under or cut off at the stem this nitrogen becomes available
in the soil for cashew plants to use.
• Some cover crops are biological sub-soilers, such as cassia, with roots that reach
down into the sub-soil up to 8 feet, bringing valuable hard-to-reach nutrients up to
the soil surface as the crops are harvested.
• In choosing a green manure crop, many factors have to be considered: the
amount of biomass, the nitrogen-fixing factor, time required to grow, and most of
all how the crop coordinates with the main crop in the particular plantation
system.
• For instance, taller crops offer the most biomass, but they require serious
equipment or massive effort to cut them down or turn them under.

43. Improvement of soil with green manure
Soil Improvements
• Strictly for its ability to improve both the soil and the crop planted.
• The benefits of using green manure crops have long been documented. Like a
cover crop, green manure protects against soil erosion, helps to retain nutrients,
suppresses weeds, recycles nutrients that might otherwise be unavailable to crops,
and leaves nutrients in the soil for the crop.
• Leguminous green-manure crops not only help to build up the soil organic matter
but also fix atmospheric nitrogen for the main crop.
• Therefore, leguminous green manure crops make excellent green manures
because they have low carbon to nitrogen ratios and will break down rapidly in the
soil.

44. • Deep-rooted grasses also make excellent green manure crops because their
roots can reach deeply into the soil to pull up leached nutrients and expand
the root zone.
• To obtain best results from green manure crops, it is advisable to
incorporate into the soil at the flowering stage during which the greatest
bulk of dry matter is present.
• It is also necessary that the green manure should be succulent and the soil
should have sufficient moisture at the time of incorporation.

45. • Weed suppression-
It is another benefit of green manure crops.
They can out-compete the resident weed population, stealing their
light, water, nutrients, and space. Also, some green manure crops will
climinate weeds through allelopathy, a form of natural chemical weed
control.

46. Mulch
• Another way that organic matter is used in cashew plantations is to cover the soil
around the manure circle with organic matter which called as mulching.
• Mulches retain soil moisture and limit weed growth on the manure circle thereby
allows the tree to utilise the applied fertiliser effectively.
• Plant residue from locally grown crops, either from cover crops or green manure
bushes, can be chipped and spread as a mulch.
• Mounding mulch against the tree trunks may cause threats of disease or insect
damage to the tree.

47. Animal manure
• Animal manures are by-products of the livestock industry.
• Nitrogen loss is greatly affected by the method of application.
• Immediate incorporation will minimize nitrogen volatilization.
• The composition of animal manure varies according to the type and age of
animal, feed consumed, bedding used, and handling system.

48. Cashew as a soil reclaimer
• Since cashew is grown in all parts of the country, it is important not only to
minimize the land degradation but also to reclaim the plantations by growing
cashew which has inherited qualities as a soil reclaimer.
• Cashew has been identified, as an ideal plantation crop for the marginal lands
where other crops can not survive.
• It is suitable for fairly steep slopes with shallow top soils because of its large
canopy and surface root system which protect the soil very well from run off and
erosion during the heavy monsoon rains.
• It has also been classified under, 'the trees used for soil improvement', because it
has the properties, which are likely to make a woody perennial suitable for soil
fertility maintenance or improvement such as
a. a dense net work of fine roots
b. the existence of a deep root system

49. • c. absence of toxic substances in the litter or root system
• d. for soil reclamation, a capacity to grow on poor soil
• e. absence of severe competition effects with other crops particularly
for water
• f. low invasiveness
• g. a high and balanced nutrient content in the foliage, and
• h. an appreciable nutrient content in the root system

50. • Some of the properties may claim cashew as a soil reclaimer as its ability to
survive in adverse soil conditions and progressively upgrade them.
• When properly managed, cashew can improve soil fertility by addition of organic
matter to the soil, reducing run off and soil erosion, increase nutrient inputs
through uptake of nutrients from deep soil horizons and bring them back to the
surface soil as crop litter.
• Adoption of improved soil and crop management practices, can increase yields
and reduce runoff, erosion and land degradation at the end.
• The improved management effects on reducing runoff and erosion were due in
part to better surface protection through a quicker cover in the seedling stage and
a denser cover throughout the bearing stage, with a more extensive root system of
cashew to capture nutrients and water.

51. • Tolerance of cashew to initially poor soil condition is an ideal character identified
for soil reclamation.
• This, in combination of fine feeder roots with tap root, high biomass production
with dense crop canopy are the other characters of cashew which show a capacity
to improve soil rather than to degrade the soil.
• Long term care and stewardship of our land is vitally important to the economy of
Sri Lanka, where major portion of our foreign exchange still depends on the
plantation sector.
• Therefore, it is our responsibility to work to enhance and maintain the
productivity of our land resource in years to come.
• However, man as the caretaker of the land can either manage or mismanage and
the future generation has to bear the consequences of his action.

52. Thank You..