Alley cropping is a specific practice in which trees or shrubs and agricultural crops are grown in alternate rows The trees are commonly pruned to limit the shading of the agricultural crop. Alley cropping can also contribute to nutrient cycling and erosion control. Bush burning is the removal of the natural vegetation cover that protects the soil surface through the use of fire. This exposes the land to the effect of wind, soil erosion, water erosion and ultraviolet radiation. Overgrazing is grazing by livestock or wildlife to the point where the grass cover is depleted, leaving bare, unprotected patches of soil. As a result, water and wind cause erosion, especially on clay soils, and the growth of poisonous plants and thorny shrubs may increase. Therefore Bush burning and Overgrazing promote soil erosion.