The main aims of soil conservation are as follows:
(1) To protect the soil from erosion.
(2) To maintain the productive capacity of the soil.
Soil erosion is a natural phenomenon by which soil is removed from rocks. Accelerated erosion due to misuse of resources of land, water and soil is today one of the most difficult and pressing problems before man. Both engineering and biological methods have been used to check the soil erosion but it is still without a plausible check. Vast tracts of fertile land are rendered useless on account of industrialisation and development.
Erosion has posed a serious challenge in the United States, South and North Africa, Japan, Mesopotamia, North China, India, Pakistan and in a number of other countries. In India, we are aware of advancing deserts of Rajasthan and erosional losses, floods etc. in other parts of the country. The problem has received the attention of forest ecologists, soil scientists and engineers only recently.
Practical methods of soil conservation are broadly grouped as follows:
(A) Biological measures,
(B) Mechanical or Engineering methods.
A. Biological Measures:
The following are the biological methods which are helpful in checking the soil erosion:
1. Agronomic practices;
2. Agrostological methods;
3. Dry farming practices.
1. Agronomic practices:
The important agricultural practices which contribute to the conservation and productivity of cultivated lands are referred to as conservation farming’s or advanced agronomical methods.
These are listed as under:
(i) Contour farming
(ii) Tillage and keeping the land fallow
(iii) Crop rotation, sowing of leguminous crops and mixed cropping
(v) Strip cropping
(i) Contour farming:
It is practiced in the hilly regions or on the slopes. In such areas the ram water is absorbed in very little amount because of its quick downward movement on the slopes. If these sloppy areas are ploughed up and down the slope, the heavy rainfall may cause gully development. Taking into consideration this defect, the sloppy areas are ploughed and seeded against the slope, i.e., in circular furrows around the slopes. This process is termed as contour farming.
The contours (circular or peripheral furrows) catch the downwardly moving water until it is absorbed in the soil. The ridges reduce the flow of water. The circular rows of plants across the slopes check the soil erosion. Thus, contour farming reduces run off, saves more water for crops, reduces soil erosion and increases the yield of crops (Fig. 25.4).
(ii) Tillage operation and keeping the land fallow:
There are several diverse opinions as to whether deep ploughing gives good result or shallow ploughing. A number of researches support the view that in dry areas, shallow ploughing gives comparatively good crop yields Shallow ploughing removes the weeds and enables the soil to absorb water. Deep ploughing of en leads to soil erosion but in the areas where rainfall is sufficiently high, deep ploughing (upto 15-30 cm deep) is effective in removing weeds and increasing crops yields.
If the land is left uncultivated and sheep, goats and other cattle are allowed to graze and sit over it for some time, the soil becomes fertile. Though this practice is useful yet it is not possible in the countries like India where exists severe problem of cereals because of thick human population.
(iii) Crop rotation, sowing of legumes and mixed cropping:
When the same crop ‘s grown in the field every year, the soil becomes depleted in certain minerals. The soil loses its fertility even after the use of fertilizers and ultimately erosion sets in. Rotation of crops is an important method for checking erosion and maintaining productivity of soil. After 2 years crop should be changed in the fields.
A good rotation should include a cultivated row crop, densely plan e small grasses and a spreading legume or a legume and grass mixture. Selection of crops for rotation should be made taking into consideration the climate, economic condition soil types, soil texture, slopes, nature of erosion, etc. Deep-rooted crops should be rotated by shallow-rooted crops.
Deep-rooted crops absorb nutrients from the deeper strata of the soil Thus, the minerals о top soil remain stored for future use by shallow-rooted plants. When the deep rooted crops le they add humus in the soil which is future storehouse of plant nutrients. Growing of Phaseolus mungo (Mung in Hindi) in Bihar, P. radiatus (Urad in Hindi) and P. mungo in U.P. in kharif season before wheat cropping improves soil fertility as well as yields of cereal crops.
In Vidarbha (Maharashtra), the rotation of cotton, jowar, and groundnut has been proved useful in maintaining the productivity of the soil. Leguminous plants play very active part in increasing the nitrogenous contents in the soil because of the fact that bacteria inhabiting their root nodules fix nitrogen of atmosphere into nitrogenous compounds such as nitrates, nitrites, ammonium salts, amino acids and proteins. The nitrogenous compounds return to the soil by way of death and decay of underground nodulated roots of these legumes. Thus, growing of leguminous plants is one of the important methods for maintaining soil fertility.
The rotation of crop serves the following purposes:
(a) Enriches the soil,
(b) Improves the soil texture,
(c) Improves water holding capacity of the soil,
(d) Improves crop production,
(e) Controls the recurrence of weeds and diseases.
Mixed cropping is another important method for increasing productivity of the soil. In this practice, one main crop and one or two subsidiary crops are grown together on the same land, as for example, growing of Arhar, Urad, Til along with millet. This practice checks the soil erosion and avoids the risk of crop failure. If one crop fails due to diseases or any other factor, the others remain ensured.
It means covering the soil surface by straw, leaves or grasses. Mulches of different kinds check soil erosion, increase soil fertility and also minimize moisture evaporation from the top soils. Various types of surface tillers and crop residues are helpful in obstructing the movement of soil particles.
(v) Strip cropping:
It is an important method which employs all the advanced cultivation practices such as contour farming, proper tillage, crop rotation, mulching, cover cropping, etc. Strip cropping is very effective and practical means for controlling soil erosion.
It is of the following types:
(a) Contour strip cropping,
(b) Field strip cropping,
(c) Wind strip cropping, and
(d) Permanent or temporary buffer strip cropping.
(a) Contour strip cropping:
It is special crops are grown on the strips across the slope on the level of contour and in the following season soil protecting crops are shown on the strips on which soil exposing crops were grown in the previous season and again in place of these soil protecting crops some soil exposing crops are sown. This practice is useful because it checks the flow of runoff water, increases the infiltration of water in the soil and prevents soil erosion. (Fig. 25.5)
(b) Field strip cropping:
It is a farming in more or less parallel strips across fairly uniform slopes but not on the exact contour.
(c) Wind strip cropping:
In this method tall growing plants (e.g. bajra, jowar, etc.) alternating with the short growing crops, such as ‘arhar’, ‘urad’ are sown in long straight strips right across the direction of wind regardless of contour.
(d) Permanent or temporary buffer strip cropping:
This is a special type of contour strip cropping in which care is taken to check the soil erosion. In this, crop rotation practice is not applied and on the strip perennial legumes and grasses are planted on permanent or temporary basis.
2. Agrostological methods:
The following are the important agrostological practices that check soil erosion:
(i) Cultivation of grasses (ley farming).
(ii) Retiring the land.
(iii) Afforestation and Reforestation.
(iv) Checking of overgrazing.
(i) Cultivation of grasses (Ley farming):
This method consists in growing grasses in rotation with agricultural crops. This practice improves the fertility of soil and helps in binding of the soil, thus preventing the soil erosion. This practice is recommended for Nilgiris and similar places which are subjected to very severe soil erosion.
(ii) Retiring the land:
Areas subjected to heavy soil erosion should necessarily be put under thick cover of grasses. Under favourable climatic conditions grazing should also be allowed for short periods. Researchers conducted at Solapur in Maharashtra have shown that grasses have good soil binding capacity. In Nilgiri hills, Tamil Nadu doobgrass (Cynodon dactylon), Dectylis glomerata, Eragrostis amabitis and E. cerbula are proved to be most effective in soil binding and in stabilizing the reserves of the bench terrace and sodding water channels.
(iii) Afforestation and reforestation:
Afforestation means growing forests at places where there were no forests before due to lack of trees or due to adverse factors such as unstable soil, aridity, or swampiness. Reforestation means replanting of forests at places where they have been destroyed by uncontrolled forest fires, excessive felling and lopping. Plantation of trees in short blocks is known as a wind break and extensive plantation of trees is called shelter belts.
Wind is a problem in dry areas. Soil erosion by wind can be checked or reduced if the soil is covered by vegetation. Wind breaks are planting of trees or other plants at right angles to prevailing wind that protect bare soil from full force of wind. Wind breaks reduce the velocity of wind, thereby decrease the soil erosion. In some cases, rows of trees are angles to prevailing wind. Wind break and shelter belt type of plantations are being done in some regions of Uttar Pradesh where desert is encroaching.
The plantation is usually done in two or three belts. Small sized plants are planted on windward side and tall trees on leeward side. Wind breaks and shelter belts reduce the wind velocity considerably and also check the transport of lifted sand and soil particles. Afforestation is the best means to check the soil erosion.
Lutz and Chandler (1946) cited the following points in support of the vegetational check of erosion:
(a) Infiltration of water is favored due to high porosity of soil under vegetation. Percolation of water helps in preserving the soil moisture which accelerates growth of vegetation.
(b) Surface accumulation of organic matter increases the water holding capacity of soil.
(c) Root systems of vegetation hold the soil mechanically and provide stability to the soil.
(d) It gives protection to soil against wind. The forest vegetation shields the soil from direct effects of drought, snow and rain.
Destruction of vegetational cover usually results in accelerated erosion, flooding and silting. The past victims of soil erosion tell the story of drastic deforestation (destruction of forests). In our country deforestation has been recognized as the most potent and powerful cause of soil erosion and efforts are being made to check it.
State forest departments in India have already undertaken this practice, although in very restricted areas and have met with good success. Forest departments in Baramulla, Gulmarg, and Banihal in Kashmir afford good examples. In Baramulla region, mixed planting of Pinus, Cednis and other species has been done. The plants are thriving well and have checked erosional losses of soil to a good degree.
In the area where plantations have not been made the soil is actively eroding. Another example is afforded by Sankaracharya Hills in the vicinity of Srinagar which was heavily eroded in the past. It has now been improved by afforestation. Forest department took up the planting of conifer species like Pinus wallichiana P. roxburghii, P. sylvestris, P. insignis, P. gerardiana, Cupressus arizonica, C. sempervirens, Juniperous species, Cedrus deodara, and broad leaved species, like Aesculus indica, Fraxinus, Juglans regia. These plants check erosion to some extent.
The efforts are being made to check the spread of Rajasthan desert towards Uttar Pradesh and the plantation is being done in that region in two or three belts. Small-sized plants are planted on the windward side and tall trees on the leeward side. On the windward side Leptadenia spartium, Cenchrus ciliaris, Balanites roxburghii, Calligonum polygonoides, Sachharum munja, Kochia indica, etc. are commonly planted and on leeward side Acacia Senegal, A. leucophloea, Ricinus communis, Prosopis spicigera, P. juliflora, Parkinsonia, etc. are being grown.
The problem of afforestation is the selection of suitable species for a given area. This can be accomplished by dividing the whole area into different catchment zones according to climate, soil and biota. Suitable species for each zone should be selected from those already growing there. Knowledge of successional trends of the vegetation will be of great help in afforestation practices. Lutz and Chandler (1946) have stated that climax vegetation in any region is most effective agent to prevent accelerated erosion. Afforestation also checks the erosion of unstable rocks probably by checking the leakage of water (Puri, 1951).
Along with afforestation and reforestation, forest management practices should also be strictly enforced which require:
(a) Control on forest fires,
(b) Extension of forest areas,
(c) Checking extensive felling and lopping,
(d) Restricted grazing in forest areas, and
(e) Formation of reserve forests.
(iv) Checking of overgrazing:
Since grazing in all the areas subjected to soil erosion cannot be completely stopped, a system of restricted and rotational grazing may be helpful in checking soil erosion to some extent. The area open to grazing for sometimes should be closed for the following years to facilitate regeneration of forest and to maintain thick ground vegetation.
3. Dry farming practices:
Dry farming is useful in those areas where rainfall is very low, uncertain and uneven in distribution. In such areas maximum conservation of water in the soil and reduction of soil erosion are the two main problems. The improved dry farming practice developed as result of researches carried out in India is an integrated rational system of cultivation of purely rained and drought enduring crops in dry areas. This practice consists in bonding, both contour and compartmental, and all other advanced agricultural practices to conserve maximum amount of rain water in the soil so as to make it available for crops during their growth period. In this, usually early maturing crop varieties are selected for cultivation.
Important dry farming regions of India are:
(3) South-west part of U.P., north-west part of M.P., and
(4) Some parts of peninsular India including dry tracts of Maharashtra, Mysore, Andhra Pradesh and Tamil Nadu.
Dry farming methods and selection of crops vary in different regions as per requirement of local conditions.
B. Mechanical Methods:
It is only in recent years that soil erosion problems have received attention of engineers. The mechanical practices of soil conservation include various engineering techniques and structures which are adopted to supplement the biological methods when the latter alone are not sufficiently effective.
These practices aim at the following objectives:
1. To reduce the velocity of run-off water and to retain it for long period so as to allow maximum water to be absorbed and held in the soil.
2. To divide a long slope into several small parts so as to reduce the velocity of run-off water to the minimum, and
3. Protection against erosion by wind and water.
Mechanical methods for soil conservation are:
(i) Basin leaching,
(ii) Pan breaking,
(iii) Sub soiling,
(iv) Contour terracing,
(v) Contour trenching,
(vi) Terrace outlets,
(vii) Gully control,
(viii) Digging of ponds and reservoirs, and
(ix) Stream bank protection.
(i) Basin leaching:
In this method, a number of small basins (water reservoirs) are made along the contour by means of an implement called basin blister. Basins collect and retain rain water for long period and also catch and stabilize downwardly moving soils of the slopes.
(ii) Pan breaking:
In some areas, soils become impervious to water and are less productive because of formation of hard sheet of clay a few feet below the surface. Such areas can be made productive and water permeable by breaking hard clay pans by means of pan breaker on contour at a distance of about 5 feet. By pan breaking, drainage and percolation of rain water is improved and soil is saved from residual run-off and erosion.
In this method hard subsoil is broken deeply by means of an implement called subs oiler. This process promotes absorption of rain water in the soil and makes the soil more loose and fit to allow luxuriant growth of vegetation.
(iv) Contour terracing:
Sometimes drainage channels or properly spaced ridges or soil mounds are formed along the contour (at right angles to the slope) to retain water in the soil and check the soil erosion. These are called terraces. Terraces are leveled areas constructed at right angles to the slope to reduce soil erosion.
Terracing may be of the following four types:
(a) Channel terracing:
This is concerned with making of wide but shallow channels on contours at suitable distance. In this process, the excavated soil is deposited along the lower edge of channel in the form of low ridge.
(b) Narrow based ridge terracing:
This process is commonly called bunding. In this a number of narrow based ridges or bunds are constructed at distance of 1into 2inacross the slope along the contour.
(c) Broad-based ridge terracing:
In this, wide but low bunds are made on contour by excavating soils from both the sides of ridge.
(d) Bench terracing:
This method involves making of wide step like platforms, the so called bench terraces, having suitable drops along contours (Fig. 25.6). Along the outer edges of bench terraces bunds of about one foot height are raised to check the downward flow of rain water and also soil erosion. The vertical drops may vary from 1into 2 m. Bench terracing is very costly process and so it should be applied in the area of land scarcity for growing money crops.
Terracing is the only practical method of soil conservation on steep land. It is an expensive method or reducing soil erosion since it requires moving soil to construct the leveled areas, protecting the steep areas between terraces and constant repair and maintenance. Many factors such as length, the steepness of slopes, type of soil, and amount of precipitation determine the feasibility of terracing.
(v) Contour Trenching:
This method involves making a series of deep pits (2′ x 1′) or trenches across the slope at convenient distance (Fig. 25.7). The soil excavated from the trenches is deposited along the lower edge in the form of bund. On the ridges tree seeds are sown (Fig. 25.7).
(vi) Terrace outlet:
In order to reduce soil erosion and to remove excess of rain water safely from the contour terraces pipe outlets are used or channels are made which are thickly covered by grasses.
(vii) Gully and ravine control:
Gully formation can be checked by the following methods:
(a) By making perimeter bunds around gullies to check flow of water through it.
(b) By growing suitable soil-binding vegetation on the gullies to check soil erosion.
(c) Diversion trenches should be made around gullies.
(viii) Ponds and reservoirs:
Small ponds and water reservoirs or dams should also be made at suitable places for irrigation and some other purposes. Various types of dams have been devised to arrest and plug gullies and thus to check soil erosion (Fig. 25.8). These dams may be (a) brush dams (b) earth dams, (c) concrete dams or (d) woven wire dams.
(ix) Stream bank protection:
Banks of ravines and rivers with high vertical drops are subjected to heavy soil erosion. The bank erosions can be checked by making the drop slopy and by growing vegetation on the slopes or by constructing stone or concrete pitch.
The problem of soil conservation is very complicated and is receiving attention of scientists and engineers. The erosion of Siwaliks has been studied by Glover and Hamilton (1935) and Gorrie (1951) and various methods have been suggested for soil conservation. Recently Pun (1949 1954) analyzed the problems from different angles and suggested that soil should be kept wider tree vegetation in order to check erosional losses and landslides.
The Central And Zone Research Institute in collaboration with UNESCO is attempting to check erosional losses in Rajasthan. The Indian Council of Agricultural Research (ICAR), especially the Waste Land Reclamation Committee, is giving attention to the problem in collaboration with some State forest and agriculture departments. Central Soil Conservation Board has established 9 research centres one each at Dehradun, Kota, Gotacamund, Bellary, Vasad, Agra, Chandigarh, Jodhpur and Chhatra to organise, co-ordinate and initiate researches on soil conservation, to meet the paucity of trained personnel’s for manning soil conservation schemes and to assist States and River valley projects technically.