Agricultural Drainage

Bulletin 871-98

Water Table Management

Water table management is a package of management practices and strategies that can be used by agricultural producers and land managers to manage drainage waters. In simple terms, water table management is the management or regulation of soil-water conditions in the profile of agricultural soils. Water table management consists of three basic practices. These are conventional subsurface drainage, controlled drainage, and subirrigation. Controlled drainage and subirrigation are relatively new techniques that have demonstrated increased crop yields.

Conventional Drainage The most common form of water table management used in the Midwest is conventional drainage. A system of drainage pipes (corrugated plastic tubing, clay or concrete tile, etc.) that outlet into a ditch or stream acts to lower the water table level equal to the drain depth through gravity.
Controlled Drainage For controlled drainage the traditional system of drainage pipes is intercepted by a water control structure. This allows the drainage outlet to be artificially set at any level between the ground surface and the drains. Raising the outlet after planting helps keep water available for plant use longer than does "free," uncontrolled subsurface drainage. This practice can also be used to recharge the water table between growing seasons. Research conducted in North Carolina indicates that controlled drainage may provide some reduction in nitrate-N losses over conventional drained cropland.
Subirrigation Mode With subirrigation, one system provides both the drainage and irrigation requirements for the crop. The water table level in the field is regulated through the subsurface drainage system using control structures. The subsurface drain spacing for subirrigation is usually 30 to 50 percent denser than that used for conventional subsurface drainage. Irrigation occurs below the ground surface, thus raising and maintaining the water table at an appropriate depth in the crop root zone.