Control of Water Erosion
Water erosion can be minimized by preventing the detachment and the transport of soil particles. A cover of vegetation and soil granulation helps to prevent the detachment of soil particles. The transportation of soil particles can be effectively minimized by artificial mechanical structures to control the effects of runoff.
Biological Methods of Water Erosion Control
Control of erosion through vegetation is called biological method. Biological methods are aimed in providing suitable cover of crops for as long period as possible during rainy season, especially at the time of heavy rainfall. A grass cover has been at least five times more effective than a bare soil in the control of soil and water loss. The biological methods are applied to control water erosion:
The term contouring refers to raising ridges and making furrows with all ridges at same level. The first line of the contour (ridge) should be laid out at eye level with a 0.5% slope towards waterways. Crops should be planted up and downhill from the line on contours. This is referred to as contour farming. Contour farming helps in conservation in low rainfall areas because each row acts as a barrier to the flow of water. In high rainfall areas, this reduces soil loss by holding a part of rain water and allowing only small volume of rain water for surface runoff. Since contours make a small embankment which store rain water at or near the point where it falls, they have a great value in controlling floods in small Watersheds. The practice of contouring increases crop yield by 10% and reduces soil loss by 50%.
If we grow crop in a long narrow area of land (strip), it is called strip cropping. Erosion Permitting crops (row crops) and erosion resisting crops (close growing crops) are alternately planted. These helps reduce the speed of runoff water coming from erosion pern-tilting strips. Also strip cropping makes it possible for water to remain in the field for becomes available to the crop. The strip cropping controls erosion slowing runoff water flow through close growing strip and by increasing infiltration rate.
Strip cropping is of four types:
Contour Strip Cropping: In this type, the crops are grown on contours across the slope in regular long and narrow strips of variable widths. This is most effective type of strip cropping.
Field Strip Cropping: In this type, the crops are planted in more or less parallel strips across uniform slopes, but not exactly on contours.
Buffer Strip Cropping: These are strips of permanent cover crops and usually located on steep and badly eroded areas.
Wind Strip Cropping: It consists of planting tall growing crops such as jazvar, bajra or corn and low growing crops alternately arranged straight and long but relatively narrow parallel strips laid right across the direction of prevailing wind.
Alternate sowing of crops on a given land is crop rotation. Crops differ in their root activity and amount of crop residue added to the soil. The dense and fibrous root system of grasses holds soil aggregates together and creates good soil structure. After the plant die they leave channels through which water can move to deeper layers. The crops in rotation may be cereals, legumes, a grass or legume or grass-legume mixture.
Crops vary greatly in their capacity to control soil erosion and building up of soil fertility due to variation in growth characteristics such as root system height and development of crop canopy. Certain crops such as green manures crop and grasses conserve the soil and build up soil fertility by addition of organic matter and nitrogen.
Cropping system is one of the most important means of prevention of preservation of good soil structure, maintenance of organic matter and soil fertility. Soil depleting crops may be sown in rotation with green manure and cover crops to maintain soil organic matter and soil structure.
Mulch refers to straws (stalks of wheat, maize, rice, cotton, etc.), stubbles (basal parts of herbaceous plants especially cereals attached to the soil after harvest), saw-dust, etc. Mulch is of special value in reducing erosion especially in periods during, which crops themselves do not protect the soil. The most desirable mulch material is left over crop residues. These dissipate the force of falling rain drops and reduce splash erosion and give water a better chance to enter water. The dead residues are absorptive and help to hold water at soil surface. Mulch also retard soil surface flow which permits more time for water to infiltrate the soil thus improves soil moisture contents and yield consequently.
A high fertile soil guards against soil erosion as it permits quick establishment of crop on soil. The crop cover dissipates the impact of falling raindrops, reduces splash erosion, velocity of runoff water, and adds organic matter to the soil thus improving soil structure.