Hydrophobicity of soil

Hydrophobicity impedes the rate and extent of wetting in many soils. It is caused primarily by organic compounds that either coat soil particles or accumulate as particulate organic matter not associated with soil minerals. Sandy textured soils are more prone to hydrophobicity because their smaller surface area is coated more extensively than soils containing appreciable amounts of clay and silt. The most important effect of hydrophobicity is changes to soil water dynamics. Hydrophobicity causes negative effects through reduced infiltration and water retention, leading to enhanced run-off across the soil surface, preferential flow pathways in the unsaturated zone of the soil, and less plant available water. Many soils that appear to readily take in water have small levels of hydrophobicity. Reduced wetting rates caused by hydrophobicity may also have a positive impact on soil structural stability. Hydrophobicity can be enhanced by soil drying, heating from fires, soil nutrients, and organic inputs.