Animal wastes are commonly considered the excreted materials from live animals. However, under certain production conditions, the waste may also include straw, hay, wood shavings, or other sources of organic debris. It has been estimated that there may be as much as 2 billion tons of animal wastes produced in the United States annually. Application of excreta to soil brings benefits such as improved soil tilth , increased water-holding capacity, and some plant nutrients. Concentrated forms of excreta or high application rates to soils without proper management may lead to high salt concentrations in the soil and cause serious on- or off-site pollution .