Known as "hydrophobicity," it is a phenomenon that is counter-intuitive: water-repelling soil. The water simply sits on the soil, unable to penetrate the hydrophobic layer contained within. Hydrophobicity is most apparent after a prolonged drought and will often disappear after an extended rain. It can inhibit the growth of plants, increase soil erosion and even increase pollution as runoff water finds alternate paths, picking up contaminants along the way.
Dead Flora and Fauna
Hydrophobic compounds naturally occur in microorganisms present in the soil and in the cells of plants and animals. Their decaying remains litter the ground and are sometimes referred to as "organic litter." Some of these compounds can best be described as the substance that make feathers waterproof or a component of a plant, such as the wax that is extracted from bayberries and made into candles. This organic "litter" can release these compounds as it decomposes, thereby adding hydrophobicity to the soil.
The intense heat of ground-level or canopy-level forest fires can hasten the release of naturally occurring hydrophobic compounds already present in organic litter. The compounds liquify and subsequently harden several inches below the soil's surface, creating a hydrophobic layer.
Coarse Textured Soils
Sandy types of soils, which are coarse-textured and contain a lot of air space between the particles, absorb the greatest amount of decayed hydrophobic residue from "organic litter," according to the United States Department of Agriculture. These types of soils transmit heat more easily than heavier clay or slurry soils and the hydrophobic particles travel deeper into the soil, due to the porous texture.