Soil conservation includes all such measures which help in protecting the soil from erosion, contour terracing and bunding, construction of bunds across gullies, levelling of unoven land and raising grass and other vegetation on land are the small measures which are usually taken by’ farmers to protect soil from erosion.
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Such methods are quite effective in areas where the degree of erosion is not serious as in the semi-arid tracts of the peninsula and part of Gujarat, Madhya Pradesh, Uttar Pradesh, Haryana and Punjab. Extensive reclamation schemes are under implementation in these states. Construction of bunds across gullies and levelling of surface, control of overgrazing by animals, and afforestation are some of the steps taken under these schemes.
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In the tropical forest areas, shifting cultivation known as jhumming in Assam, ponam in Kerala, podu in Andhra Pradesh and Orissa, and bewar, masham, penda and beera in different parts of Madhya Pradesh is a serious problem. It is necessary to educate the adivasis, who practise it, in better farming techniques. The Central Government created the Central Conservation Board in 1953 to coordinate the soil conservation schemes on an all India basis.
Methods of Soil Conservation
1. Contour Ploughing:
If ploughing is done at right angles to the hill slope, following the natural contour of the hill, the ridges and furrows break the flow of the water down the hill. This prevents excessive soil loss, as gullies are less likely to develop and also reduce run-off so that plants receive more water. Row crops and small grains are often planted in contour pattern so that the plants can absorb much of the rain, and erosion is minimized.
2. Terracing:
Slopes may be cut into a series of terraces with sufficient level ground on each terrace for cultivation, and an outer wall at the edge to retain the soil and to slow down the flow of rain-water down the slope.
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Terracing is widely used in Monsoon Asia for wet paddy cultivation, as the excess water and silt can be retained at each terrace to form flooded paddy-fields. Many tree crops such as rubber are also planted on terraces to combat soil erosion. Terraces are also used in temperate and semi arid regions where slopes are steep. Terracing enables farmers in mountainous regions to utilize the steep ground on the favoured ‘sunny slopes’ of valleys for vines or other crops.
3. Strip Cropping:
Crops may be cultivated in alternate strips, parallel to one another. Some strips may be allowed to lie fallow while others are sown to different kinds of crops, e.g. grains, legumes, small tree crops.
The various crops ripen at different times of the year and are harvested at intervals. This ensures that at no time will the entire area be left bare or exposed. The tall-growing crops act as windbreaks and the strips, which are often parallel to the contours, help to increase water absorption by the soil by slowing down run-off.
4. Fallowing:
Sometimes it is important to allow much used land to rest or lie fallow, so that the natural forces can act on the soil. The decayed natural vegetative matter helps to increase the plant nutrients in the soil. Fallowing also increases the sub-soil moisture and improves the general structure of the soil.
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Winter fallow is commonly practised in temperate regions after the harvest, but cultivation is resumed in the spring after the snow and frost have weathered the top soil. Long periods of fallow cannot be allowed, however, in intensively run farms as farmers cannot afford it.
In semi-arid areas fields may be allowed to lie fallow for several years, though they are often ploughed or mulched, i.e. spread with straw or the stubble of the previous year’s harvests. This enables them to build up a sufficient supply of moisture by reducing evaporation, and a crop can be grown every few years. This system of dry farming is practised in western U.S.A. and in parts of Mediterranean Europe.
5. Cover Cropping:
In some cases, as in plantations, where the gestation period of tree crops is long, cover crops may be inter-planted between the young trees. Creepers are preferred because they spread around and form a useful cover that protects the top soil from the full force of the tropical downpours.
Care must be taken that the cover crop does not compete with the young trees for the essential plant nutrients, and leguminous crops are often used because they add nitrogen to the soil. Cover crops may be grown simply to protect the soil or may consist of other valuable plants such as vegetables which provide an income while the plantation crop matures. Some such catch crops, e.g. cotton, maize or tobacco, should be avoided because they exhaust the soil or promote soil erosion instead of preventing it.
6. Crop Rotation:
It is not advisable to grow the same crop in the same field for more than two years in succession as the crop will tend to exhaust one particular kind of mineral nutrient. For example potatoes require much potash, but wheat requires nitrates.
Thus it is best to alternate crops in the fields. Legumes such as peas, beans, clover, vetch and many other plants, add nitrates to the soil by converting free nitrogen in the air into nitrogenous nodules on their roots. Thus if they are included in the crop rotation nitrogenous fertilizers can be dispensed with.
By rotating different types of crops in successive years, soil fertility can be naturally maintained. The best known crop rotation is the Norfolk Rotation which involves the growing of four crops in a given field over a period of four years.
These crops are wheat (cereal); clover or beans (legume); barley (another cereal); and turnips or sugar-beet (root crops). In fact on most temperate mixed farms all these crops will be grown on some of the fields each year but the fields in which they are grown will be different in each year so as to maintain the rotation for any particular field. The land can be much more profitably used by employing rotation systems than simply allowing it to lie fallow if moisture and other conditions allow this practice.
7. Crop Diversification:
This practice is often like crop rotation in that it helps to maintain soil fertility. Where annually-harvested crops are grown they can be alternated in the field. Where perennial crops like tree crops are grown, however, the chief importance of crop diversification to the farmer is economic. In particular it reduces the danger of depending on a single crop (monoculture) when world commodity prices are falling.
All the primary commodities, e.g. rubber, oil palm, cocoa, cotton, are subject to great fluctuation in prices, much depending on the demand of the western world. Over-dependence on one crop can be disastrous to the national economy as well as to the individual farmer, as in the case of Brazil’s coffee, Ghana’s cocoa, or Malaysia’s rubber, when prevailing prices for the major money-earning crop are low.
Crop diversification overcomes this difficulty as when one crop is only fetching low prices another may be in good demand. Another great advantage of crop diversification is that all types of land can be used, e.g. rubber can be grown on hill slopes, oil palm on flat plains, coconuts on sandy soils. Thorough crop diversification on a national and local level can lead to the most economic use of land.
8. Water Management:
One of the major ways in which land can be improved for farming is by water management. By regulating the amount of water in the soil aeration can be improved, activity by useful bacteria can be stimulated and crop yields can be improved. In addition, by draining or irrigating land, areas which are marginal or useless in their natural state, such as deserts or swamps can be brought into agricultural production –
It should be emphasized that drainage and irrigation are interdependent. Where irrigation is used it is important also to provide drainage facilities, so that the irrigation water can be kept moving and not become stagnant. Similarly in drained areas, irrigation must be applied to prevent unwanted sea-water from seeping into the drained land. In other words a balance must be carefully maintained.
(a) Irrigation:
When a region does not have sufficient natural precipitation to meet the plants’ moisture requirements, an artificial supply of water is necessary. This is known as irrigation. The amount of extra water needed depends much on the type of crops grown the prevailing temperature and humidity, the kind of soil and the physical conditions of the surrounding districts. Irrigation is one of the oldest agriculture techniques practised by men, and has many advantages over simple reliance on natural water supplies.
(i) The supply of water by irrigation is regular and reliable, whereas rainfall is often seasonal or unpredictable. In desert areas the use of irrigation allows cultivation to take place where it would not otherwise be possible.
(ii) Irrigation water supplied by rivers in flood often carries much silt which adds to the soil of the fields, enhancing fertility and thus crop yields.
(iii) With irrigation, cultivation can be done all the year round and not only during the rainy season. This allows better use to be made of the land.
(iv) In desert areas the constant flow of irrigation water through the soil helps to reduce the salinity of the soil. If, however, the water is allowed to evaporate in the fields this increases the salt content.
(v) Modern multi-purpose dams not only provide water for irrigation but also help to control floods, generate hydro-electric power and improve the navigability of the rivers. Water for irrigation may be obtained in a number of ways of varying complexity. The various types of irrigation are described below:
(i) Lifting Devices:
Water may be simply lifted from a well, river or canal by a bucket to the fields. Such devices as the shaduf the Archimedean screw and various kinds of water wheel or treadmill have been in use for thousands of years. In modern times diesel steam or electrically operated pumps can be used. They are especially useful where water is obtained front a deep well rather than from canals.
(ii) Basin Irrigation:
This method has been practised in Egypt for many centuries but is of less importance today. When the Nile rises in summer, part of the flood-water is allowed to flood basin-like fields on either side of the river. The water is controlled by sluices. Basin irrigation, using canal-water rather than river water is also used to grow paddy In the U.S.A.
(iii) Tanks:
Tanks are small reservoirs used for storing water which falls in the rainy season. They are common in southern India and Sri Lanka. The water stored is rarely sufficient for use all the year round but does lengthen the growing season.
(iv) Canal Irrigation:
Canals which lead irrigation water from rivers or storage lakes are the most important feature of irrigated lands. Inundation canals lead off water from a river in time of flood.
These are simple but do not provide water all the year round. Perennial canals are fed by water stored behind a large dam or barrage and can thus be supplied all the year round. Storage barrages feed canals not only below the dam but also above because, by raising the level of the river behind the dam, water can be led into higher level canals.
(v) Overhead Irrigation:
This is a modern system and is now practised in many parts of the world. Sprays and sprinklers are set up in the fields and supplied with water by hoses from public water supplies. The initial cost of the equipment is high and water must be continually pumped. The method is however a common one in the U.S.A., Britain and Europe.
(b) Drainage and Land Reclamation:
In very wet or low-lying areas it improves the land if drainage work is undertaken to remove excess water. Drainage not only removes unwanted water but also helps to fin-prove soil porosity and aeration, reduces soil acidity or sourness and makes the soil easier to work.
Plant roots can penetrate deeper into the soil giving bigger crops and better quality harvests. Nitrification and nitrogen-fixing by leguminous plants and by bacteria are encouraged and at the same time the plants’ liability to fungus attack is reduced. Drainage is carried out by a network of pipes open drains and ditches which carry off the unwanted water.
Open drains are used in swampy areas or on damp, peaty uplands but pipes are often laid 0.3 to 1.2 metres (2 to 4 ft) below the ground in temperate farmlands. They are more expensive than open ditches to construct at first but are inexpensive to maintain and do not interfere with farm work. Open ditches are easily and cheaply dug but must be constantly cleared of weeds and unwanted animal or insect life, and they interrupt the fields, hindering ploughing or harvesting.
It is also possible in low-lying areas fringing the sea to reclaim additional land by using drainage techniques. This has been done in the Netherlands, the Fens of Britain and in many other flood-prone coastal areas and river basins all over the world. The land is first ringed with dykes and sea-walls which keep out the water, and then pumped dry by means of windmills (in the past) or diesel pumps.
When the land is dry it must be flushed with water to remove salt from the soil and is then used for pasture or arable land. The polders or reclaimed lands form much of the best farmland in the Netherlands, supporting dairying, horticulture and arable farming.
Care has to be taken to prevent sea-water seeping in underground and impregnating the soil with salt, and another difficulty is that, as the ‘new’ land gradually becomes drier over the years, it shrinks and compacts so that it lies well below sea-level. Sea walls and dykes have to be carefully maintained to prevent flooding of such low-lying lands.
(c) Bunding:
Contour bunding is the construction of small bunds across the slopes of the land on a contour so that the long slope is cut into a series of small ones and earth contour bunds act as a barrier to the flow of water, thus, making it ‘walk’ rather than ‘run’ and at the same time impounding a greater part of water against the bund to increase the soil moisture.
(d) Control of Gully Erosion:
Gully control by the diversion of runoff proved to be an economical measure. The best method of controlling existing gullies is to re-establish vegetation. Two of the most important types are the sod strip eroded earth till.
(e) Wind Break:
The principal method of reducing surface velocity of wind, upon which would depend the abrasive and transportation capacity, are vegetal measures.