Internal drainage describes the degree and persistence of soil wetness and is influenced by slope, soil infiltration rate, soil texture, depth to water table and depth to impermeable layers. This internal drainage determines irrigation needs and timing. It directly affects the amount of water retained for crop use while also allowing sufficient movement of water within the soil to minimize saturation of the pore space. This will encourage good, healthy root and plant growth. Excessive drainage and rapid water loss can result in crop stress due to a lack of moisture and nutrients. Soils with poor internal drainage can result in waterlogged soils, increased disease potential to crops, nitrogen losses due to denitrification, and, in some areas of the country, possible accumulation of salts.

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