Various methods adopted for the soil and water conservation in many countries are presented below: 1. Conservation Tillage 2. Deep Tillage 3. Conservation Farming 4. Terracing 5. Conservation Bench Terraces 6. Water Disposal 7. Broad Bed and Furrow System 8. Ridging and Tied Ridging 9. Contour Furrows/Contour Bunds 10. Low-Cost Measures.
Method # 1. Conservation Tillage:
This umbrella term can include reduced tillage, minimum tillage, no-till, direct drill, mulch tillage, stubble-mulch farming, trash farming, strip tillage, plough-plant. In countries with advanced soil conservation programmes, the concept of conservation tillage is the main theme of the recommendations for cropland. The application is mainly in mechanized high production fanning with good rainfall, or for the control of wind erosion where there is large-scale mechanized production.
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It is less applicable to low input level crop production or subsistence agriculture. The principles are equally effective in any conditions to maximize cover by returning crop residues and not inverting the top soil and by using a high crop density of vigorous crops. Conservation tillage also has the advantage of reducing the need for terraces or other permanent structures.
Method # 2. Deep Tillage:
One of the reasons for low yields in semi-arid areas is the limited amount of moisture available to crop roots. The available moisture will be increased if the rooting depth is increased with deep tillage. Deep tillage is beneficial for some crops and on some soils. Also deep tillage requires greater draught power which is usually in short supply in semi-arid areas. Ripping or sub-soiling can be beneficial, either to increase the porosity of the soil, or to break a pan which is reducing permeability. The application of this technique to subsistence farming will be difficult.
Method # 3. Conservation Farming:
Like conservation tillage, this title covers many different farming techniques. It includes any farming practice which improves yield, or reliability, or decreases the inputs of labour or fertilizer, or anything else leading towards improved land husbandry, which gives foundation of good soil conservation. Farming on a rade is well established in India. Cultivations and planting are done on a gentle gradient, sometimes together with graded channel terraces.
This encourages infiltration but permits surplus run-off at low velocities. Sometimes this may be combined with simple practices to encourage infiltration such as returning crop residues. Strip cropping is most useful on gentle slopes, where it may reduce erosion to acceptable levels without any banks or drains. Rotations are another well established and simple practice. Fallowing is well established and successful in some circumstances but not others.
Mixed cropping and inter-planting are widely applied traditional techniques. A combination of crops with different planting times and different length of growth periods spreads the labour requirement of planting and of harvesting and also allows mid-season change of plan according to the rain in the early part of the season.
Another possible advantage may arise from the use of legumes to improve the nitrogen status for the cereal crop. Theme of mixed cropping, intercropping and relay cropping are better farming systems. Surface mulching has the advantage of providing protective cover at a time when crop cover is not practical. It improves infiltration and may also beneficially reduce soil temperature.
Method # 4. Terracing:
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Terraces have widespread application in semi-arid areas. Level terraces may be appropriate where irrigation is available and intermittent level terraces are used for run-off farming. Bench terracing has also been used in many countries for soil and water conservation. There may also be circumstances where a combination of shallow soils with limited storage capacity and heavy rain, results in frequent surface run-off which calls for a system of graded channel terraces, either without storage or with some storage and a designed overflow.
The problem is that any such system is likely to be expensive in relation to the productivity of the land and it is difficult to maintain grassed waterways as disposal channels when rainfall is limited and unreliable. Level terraces for dry land farming have been extensively used in the past in many countries and nowadays are increasingly not maintained or abandoned as the maintenance becomes uneconomic or impossible because of labour shortages.
Method # 5. Conservation Bench Terraces (CBT):
Conservation bench terraces is another type of rainfall multiplier, using part of the land surface as a catchment to provide additional run-off onto level terraces on which crops are grown. The method is particularly appropriate for large- scale mechanized farming. There is a soil erosion hazard during high-intensity summer storms, but CBTs are as effective at controlling erosion and more effective at reducing the overall run-off. The gentle slopes of 0.5-1.5 per cent are most suitable although the system has been used up to 6 percent in some countries. As with all terracing, a steeper slope requires more earth moving.
A deep soil is required, both to provide sufficient soil moisture storage and also to lessen the effect of cutting during the construction of the terraces. Good permeability is also required so that the contained flood water can be absorbed quickly. Smooth slopes are an advantage where large mechanized farming can be made more convenient by constructing all the terraces parallel and of equal width.
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Precise leveling of the bench terrace is important to ensure uniform buildup of soil moisture. The main design factors are the width of the levelled terrace and the ratio of the area of the terrace to the catchment area. Typical widths are from 10 meters on land of 5-6 per cent, to 30 meters at 2 per cent and 50 meters or more at one per cent. The most usual practice is for the bench terrace to be level along its length, but there have been a few trials with the terraces on a gentle gradient of 1:400 to encourage safe disposal of excessive run-off.
Method # 6. Water Disposal:
In semi-arid conditions, it is seldom appropriate to divert surface run-off from arable lands and the same arguments largely apply to cut-offs or diversion drains put in at the top edge of arable land in order to protect it from surface run-off from uncultivated higher land. There could be special circumstances, such as a shallow saturated soil which would be less damaged if water coming down from above could be diverted.
The difficulty is that the drain may also divert run-off during gentle storms which might have been usefully absorbed by the arable land. The use of diversions will therefore be limited to cases where there is uncontrolled flood run-off in a channel or gully which will be wasted unless it is diverted to some useful purpose.
When there is a risk that any structure intended to gather run-off may be overtopped in heavy storms, it is important to deliberately provide planned overspills which can act as safety valves and make sure that the run-off is discharged in places where it will do least damage.
Method # 7. Broad Bed and Furrow System (BBF):
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The Broad Bed and Furrow system has been mainly developed at the International Crops Research Institute for the Semi-arid Tropics (ICRISAT) in India. It is a modern version of the very old concept of encouraging controlled surface drainage by forming the soil surface into beds. The recommended ICRISAT system consists of broad beds about 100 cm wide separated by sunken furrows about 50 cm wide.
The preferred slope along the furrow is between 0.4 and 0.8 percent on vertisols. Two, three, or four rows of crop can be grown on the broad bed, and the bed width and crop geometry can be varied to suit the cultivation and planting equipment. In India, the system has been used mainly on deep vertisols (heavy black clay soils sometimes called cotton soils). Wide beds are used on a gentle grade and they are formed by ox-drawn wheeled tool carriers.
Method # 8. Ridging and Tied Ridging:
This method is also known as furrow blocking, furrow damming, furrow diking and basin listing. The principle is to increase surface storage by first making ridges and furrows, then damming the furrows with small mounds, or ties. Graded ridges alone will usually lead to an increase of surface run-off compared with flat planting, while tied ridges will decrease the run-off and increase the storage. In different seasons either of these two effects may be preferable.
An interesting possibility is to use tied ridging in connection with sprinkler irrigation to allow higher application rates at low pressure. Tied ridging is usually associated with mechanized farming. There have been some attempts at achieving it with ox-drawn implements, but the system really needs high draught for speed and precision, which is required if the ridges are to be re-ridged or split in subsequent years. Either ridging alone or tied ridging has occasionally been practised using hand labour, but the high labour requirement usually makes this unpopular with subsistence farmers. Also hand-made ridges are usually less efficient.
Method # 9. Contour Furrows/Contour Bunds:
They are also known as contour bunds and strip farming. These are variations on the theme of surface manipulation which require less soil movement than conservation bench terracing and are more likely to be used by small farmers, or in lower rainfall areas. The cropping is usually intermittent on strips or in rows, with the catchment area left fallow.
The principle is the same as conservation bench terraces that is to collect run-off from the catchment to improve soil moisture on the cropped area. On heavier soils, contour bunds may be less effective because of the lower infiltration and prevalent of waterlogging.
Contour bunds are also used for a combination of soil conservation and water conservation. If the contour furrows are not laid out precisely on the contour, or are built with some irregularities, there may be a danger of uneven depths of ponding behind the bank.
This can be reduced by smaller bunds at right angles, but as with tied ridging, these bunds should be lower in height than the main ridges so that if there should be any overtopping it will be laterally along the contour and not over the bund and down the slope. Sometimes the emphasis is on the excavated furrow which collects water, so that in exceptional storms the run-off can overflow without damage.
Method # 10. Low-Cost Measures:
The discussion of terracing and conventional conservation works clearly points to the use of simple and easily applied measures. The first of these should always be farming on the contour. This alone can reduce soil loss to approximately half of what it would be with cultivation up and down the slope.
Although rainfall in semi-arid areas will be less in total, it can still include very damaging storms and so it will usually be beneficial to have some form of structure which will slow down the surface run-off, encourage the deposition of suspended material and reduce the concentration of surface run-off in minor depressions.
Structures on the contour are simpler and cheaper than graded channel terraces. A general term for simple structures on the contour is ‘stop-wash lines” which correctly defines their purpose. The form of such lines will depend on what materials are available. On stony ground, using the stones to build rock lines serves the dual purpose of clearing them from the field as well as building the stop-wash lines.
Where stones are not available, lines can be formed by piling up crop residues, perhaps with a few shovels of soil and progressively built up later by adding weeds from hand hoeing. No design is necessary, but the general principle is that there is not much point in building large or high structures, particularly if built from stone, since they will be very permeable and in general a larger number of small barriers will be more effective than a small number of large structures.
Grass strips can also be used as stop-wash lines and live hedges with drought-resistant species are sometimes planted for the same purpose. In areas with higher rainfall, grass may be densely planted to cut for fodder and cause a terracing effect. When stop-wash lines are intended to divert water out of small channels, it is desirable to reduce the permeability at this point. This is done using the principle of the reverse filter.
The main structure is composed of large stones, then on the upstream side smaller stones are packed, but large enough so that they cannot be washed through the gaps in the large stones. Upstream of the small stones a layer of gravel is added.
Water will still flow through the structure, but slowly and it will build up in the depression and flow out on either side eventually finding a way through the rock barrier and continuing its path down the slope. This same principle can be used on a larger scale for gully control structures. Some applications of stone lines have the primary objective of water harvesting rather than soil conservation.