ABSTRACT
Artificial subsurface drainage is required on many agricultural lands to remove excess precipitation and/or irrigation water in order to provide a suitable soil environment for plant growth and a soil surface capable of physically supporting necessary traffic, e.g., for tillage, planting, and harvesting. Although this drainage makes otherwise wet soils very productive, subsurface drainage alters the time and route by which excess water reaches surface waters and can carry nutrients, pesticides, bacteria, and suspended solids to surface waters and cause nonpoint source pollution problems. The net water quality impact of subsurface drainage considered here is determined by comparison to the same cropping system not having subsurface drainage (not on the fact that the existence of adequate drainage will affect land use). The degree of pollutant transport with surface runoff and subsurface drainage is determined by the product of the volumes of water and the pollutant concentrations in the water. These are both influenced by environmental conditions, pollutant properties, and management factors, and their interactions with subsurface drainage are discussed.
