The practice of soil conservation involves using various methods to reduce soil erosion, to prevent depletion of soil nutrients, and to restore nutrients already lost by erosion, leaching, and excessive crop harvesting. Most methods used to control soil erosion involve keeping the soil covered with vegetation.
In conventional-tillage farming, the land is plowed, disked several times, and smoothed to make a planting surface. If plowed in the fall so that crops can be planted in the spring, the soil is left bare during the winter and early spring months-a practice that makes it vulnerable to erosion.
To lower labour costs, save energy; and reduced erosion, an increasing number of farmers are using conservation-tillage farming, also known as minimum-tillage or no-till farming, depending on the degree to which the soil is disturbed. Farmers using this method disturb the soil as little as possible in planting crops.
For the minimum-tillage method, special tillers break up and loosen the subsurface soil without turning over the topsoil, previous crop residues, and any cover vegetation. For no-till farming, special planting machines inject seeds, fertilizers, and weed killers (herbicides) into site made in the employed soil.
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In addition to reducing soil erosion, conservation tillage reduces fuel and tillage costs, water loss from the soil, and soil compaction, and it increases the number of crops that can be grown during a season (multiple cropping). Yields are as high as or higher than yields from conventional tillage. Depending on the soil type, this approach can be used for three to seven years before more extensive soil cultivation is needed to prevent crop yields from declining. But conservation tillage is no cure- all. It requires increased use of herbicides to control weeds that compete with crops for soil nutrients.
Today conservation tillage is used on almost one-third of world, cropland and is projected to be used on over half by 2010. The ecologists that using conservation tillage on 80% of cropland would reduce soil erosion by at least half. So for the practice is not widely used in other parts of the world.
Contour Farming, Terracing, Strip Cropping, and Alley Cropping: Soil erosion can be reduced 30% to 50% on gently sloping land by means of contour farming- plowing and planting across rather than up and down the slopped contour of the land. Each row planted at a right angle to the slope of the land acts as a small dam to help hold soil and slow the runoff of water.
Terracing can be used on steeper slopes. The slope is converted into a series of broad, nearly level terraces with short vertical drops from one to another. Some of the water running down the vegetated slope is retained by each terrace. Thus, terracing provides water for crops at all levels and. decreases soil erosion by reducing the amount and speed of water runoff. In areas of high rainfall, diversion ditches must be built behind each terrace to permit adequate drainage.
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Strips of dense, deep-rooted vetiver grass can be planted along the contours of sloping cropland to slow sheet erosion. This grass, native to India, can survive in all climates. It requires no maintenance, won’t spread, and can be established at 1% to 10% of the cost of other measures. Applying a thick mulch of crop residue can also prevent most erosion on slopes of up to 15%.
In strip cropping, a series of rows of one row crop, such as corn or soyabeans, is planted in a wide strip; the next strip is planted with a cover crop, such as alfalfa, which completely covers the soil and thus reduces erosion. The alternating strips of row crops and cover crops reduce water run-off and help prevent the spread of pests and plant diseases from, one strip to another. They also help restore, soil fertility if nitrogen-rich legumes such as soyabeans or alfalfa are’ planted in some of the strips. On sloping land, strip cropping can reduce soil losses up to 75% when combined with terracing or contour farming.
Erosion can also be reduced by alley cropping in which crops are planted in alleys between hedgerows of trees or shrubs that can be used as sources of fruits and fuelwood. The hedgerow trimmings can be used as mulch for the crop and fodder for livestock.