Factors that affect soil permeability include grain size, void ratio, water impurities and the volume of air or organic matter entrapped with the soil. Permeability is approximately proportional to the square of the grain size. Soil quality and permeability may vary greatly from one layer of soil to another.
Permeability is a property that determines how well soil transmits air or moisture. Permeability may be affected by the volume of soil comprised of open space, interconnection of porous materials within the soil and the degree of saturation. Soil permeability is commonly determined by measuring the rate of water flow through the soil over a set period of time.