Drainage Water Management
News Feature 3/26/2013
Drainage Water Management
Tile drainage has become popular in areas where soils have poor internal drainage because it helps to convert land that would otherwise be too wet to consistently farm into highly productive cropland. While the benefits of tile drainage are improved trafficability and increased crop yields, the practice also delivers nitrates and phosphorus to stream systems which has a detrimental impact on water quality.
One strategy that can be used to reduce nitrates in tile drainage water is drainage water management. With drainage water management, water level control structures are included as a part of the tile drainage system. These control structures are used to manipulate water levels at different times during the growing season. The greatest nitrate removal benefits occur when water levels are maintained in the biologically active zone where nitrates can be converted to nitrogen gas by denitrifying bacteria. With drainage water management, water levels are maintained at a higher level during the summer growing season and over the winter after fall harvest. Water levels are drawn down in the early spring before planting and in the fall before harvest. A properly managed system can also increase crop yields by conserving water in the soil profile for crops to utilize.
When is drainage water management a good fit for a new or an existing tile drainage system? Generally drainage water management is unfeasible on land slopes greater than about one percent. It may be possible to retrofit existing tile installations with water level control structures depending on how the tile layout fits with the field topography. Tile systems utilizing drainage water management do not require closer tile spacing, but tile layout should be aligned with the field’s contours as much as possible in order to provide the most complete coverage and consistent water levels across the field.
Funding is available through the EQIP program for water level control structures (NRCS Practice Standard 587) and for the annual management to control water levels (NRCS Practice Standard 554). Related EQIP practices that can be utilized to reduce nitrates in tile drainage effluent are denitrifying bioreactors (NRCS Practice Standard 747) and vegetated subsurface drain outlets, also referred to as saturated buffers (NRCS Practice Standard 739). For more information on any of these practices, contact your local NRCS field office.
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