Loss of soil fertility: Erosion

When land is cleared of its natural vegetation, such as forest or grassland, the soil begins to lose its fertility. Some of this occurs by physical erosion. Erosion is the wearing away and transportation of land surface by running water, wind, ice, or other natural agents. Once the protection of the vegetative cover is lost, the soil is exposed directly to water and wind, which remove the loosened soil upper layers, where the most fertile organic matter is found. The less organic matter present in the soil, the more vulnerable the soil is to further erosion. Once erosion starts, the process can easily accelerate. The loss of soil fertility is much faster in warmer and wetter climates, such as tropical rain forests, than it is in colder or drier climates.   

Population pressures have led to overgrazing rangelands, deforestation, and destructive crop practices like clearing and burning steep, forested slopes and plowing grasslands. All these activities degrade or remove natural vegetation, causing the underlying soil to become much more susceptible to the destructive action of erosion. The result is a vicious downward cycle of deterioration—land degradation. Such land degradation results in a reduced productive potential and a diminished capacity to provide benefits to humanity.

              

                         

All forms of agriculture lead to soil loss, but the rate of loss varies with the crop and the methods of agriculture. Land used for row crops and small grains without soil conservation practices result in greater erosion loss. Worldwide, erosion removes about 25.4 billion tonnes of soil each year. Erosion is estimated to be worse now everywhere.                               

Consequences of erosion: Sediment Damage

Much of the eroded soil ends up in waterways causing downstream sedimentation which is a serious environmental effect of modern agriculture. Sediments fill in otherwise productive waters, destroying some fisheries. Nitrate, ammonia, phosphates, and other fertilizers carried by sediments can cause eutrophication in downstream waters; the resulting buildup of algae reduces fish production. Polluted sediments also can transport toxins. Sediment damage costs the US about $500 million/year in dredging expenses.