ABSTRACT
Soil erosion implies detachment, transport, and deposition of soil by energy from water, wind, or gravity. Specific sources of energy to detach and transport soil are called ‘‘agents’’ of erosion. Soil erosion is a natural process and is responsible for formation of the most fertile soils, such as alluvial soils of the river valleys (e.g., Indus, Ganges, Euphrates, Yangtze, Nile) and loess soils of the savannas (e.g., Loess Plateau in China, the Palouse region of northwestern United States). The natural rate of erosion may be less than 0.5mmyr1, and often as low as 0.1mmyr1. The natural processes, however, can be accelerated by anthropogenic activities drastically exacerbating the rate of soil detachment, transport, and deposition. In contrast to the natural process, the accelerated soil erosion is an extremely destructive process leading to severe adverse effects on long-term productivity on-site, and pollution of natural waters and sedimentation of waterways and reservoirs off-site. Anthropogenic activities that accelerate the soil erosion process include deforestation, biomass burning, conversion of natural to agricultural ecosystems, and plowing especially up and down the slope for monoculture of open-canopy crops (e.g., corn) without protective ground cover of crop residue or a cover crop. The accelerated rate of erosion may be 0.5mmyr1 to 10mmyr1. For loess-derived soils, such as those in the Yangtze basin in China, the accelerated rate may be several cm yr1 causing severe problems of sedimentation off-site.
