Soil drainage is defined as the rate and extent of water movement in the soil, including movement across the surface as well as downward through the soil. Slope is a very important factor in soil drainage. Other factors include texture, structure, and physical condition of surface and subsoil layers. Soil drainage is indicated by soil color. Clear, bright colors indicate well-drained soils. Mixed, drab, and dominantly gray colors indicate poor drainage. Low-lying areas within the landscape receive run-off water. Frequently, the water from these areas must escape by lateral movement through the soil or by evaporation from the surface, as poor structure and other physical influences do not allow drainage through the soil. Continuous, cemented hardpan layers such as caliche also greatly reduce the internal drainage through a soil profile.

Too much or too little water in the soil is equally undesirable. With too much water, most plant roots will suffocate due to a lack of oxygen. Where there is too little water, plants will wilt and eventually die. The most desirable soil moisture situation is one in which approximately one-half of the pore space of the soil is occupied by water.

Source: University of Arizona Cooperative Extension. 1998. Arizona Master Gardener Manual: Chapter 2, Soils and Fertilizers. Tucson, AZ. Available at (verified 19 August 2004).

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