Tropical soils are opened to erosion agents (water and wind) due to overgrazing, deforestation and inappropriate methods of crop production with resultant reductions in soil productivity of the degraded land.
The degree of occurrence however differs from one location to the other. Despite these differences, soil erosion is a major national problem.
This problem can be reduced to an acceptable level by adopting appropriate farming techniques and practices as will be pointed out in this unit.
Water and Wind Erosion Defined
Erosion, either by water or wind, is the washing away of the topsoil from a piece of land. It causes a lot of damage to the farmland such as listed below:
Erosion first removes the topsoil. Topsoil affords the best root environment by providing the best structure, the most air, and an active population of living organisms. Once the topsoil is lost, only the less productive subsoil remains.
The topsoil contains most of the soil’s organic matter and plant nutrients. Erosion carries away nitrogen, phosphorus, and any nutrient stored mostly in organic matter.
As erosion strips away the soil surface, the profile becomes thinner, decreasing the root zone. This is a particular problem on already shallow soils. A major effect of this shrinking root zone is a reduced value of total water-holding capacity.
Gullies cut up fields into odd-shaped pieces and make it very difficult to operate farm equipment.
Eroded soil contains nutrients and pesticides that pollute lakes and streams. For instance, large fish kills have occurred in streams fed by runoff water from fields treated with soil insecticides. A Conservation Foundation study of 1985 estimates that 30% of American waters are exposed to enough runoff to chronically affect fish.
The soil washed away by erosion settles in streams, lakes, harbors, and reservoirs. About 760 million tons of farmland sediment reaches surface waters each year.
Water erosion removes the topsoil, reduces yields, and deposits sediments in streams, lakes, and reservoirs. Wind also strips the topsoil, blows away the smallest soil particles, and buries ditches and other structures.
Falling raindrops and running water detach soil particles from the soil surface and carry them away. Depending on the slope, erosion removes soil as a sheet or creates rills and gullies. Water erosion is promoted by bare and erodable soil, long or steep slopes, and the lack of conservation practices.
Soil scientists use the Universal Soil Loss Equation to compute soil loss. The USLE accounts only for losses from sheet and rill erosion and will understate soil loss where there is ephemeral or gully erosion. Using the USLE, a specialist can suggest practices to keep a farm productive.
Growing vigorous crops, maintaining organic matter, and avoiding over tillage and compaction help to control erosion. Both conservation tillage and crop rotation sharply curb erosion.
Contour tillage, contour strip- cropping, and terraces are effective ways to slow runoff. Where these are not enough to stop runoff, they may be combined with grassed waterways or outlets to carry the excess off the field without erosion.
Read Also: General Importance of Soil Organic Matter
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