Livestock then eat the crops producing manure, which is returned to the soil, adding organic and mineral forms of nitrogen. The cycle is complete when the next crop uses the amended soil.[1] To increase food production, fertilizers, such as nitrate (NO3) and ammonium (NH4), which are easily absorbed by plants, are introduced to the plant root zone. However, soils do not absorb the excess NO3 ions, which then move downward freely with drainage water, and are leached into groundwater, streams and oceans.[2] The degree of leaching is affected by: