The position of a soil in the landscape also influences its hydraulic loading. Soils near a hilltop often shed water, either by runoff over the surface or by lateral flow within the soil. Soils lower on the hillside and where the slope begins to flatten out often receive excess water from the higher positions. These soils are more susceptible to leaching from the added hydraulic loading. Sorption refers to the binding of chemicals to particles of organic matter and clay in the soil.
Sorption retains chemicals in the soil, where they can be degraded.
Thus the higher the sorption potential, the lower the risk of groundwater contamination. Sorption potential depends on organic matter content and clay content. Organic matter content is the most important variable affecting sorption of pesticides. Organic matter provides the greatest number of binding sites because it has an extremely large surface area and is very reactive chemically. Organic matter content in soil depends on climate, vegetation, position in the landscape, soil texture, and farming practices.