ST. PAUL, Minn. (5/24/2010) --Many soils in Minnesota and the upper Midwest are fertile, but only made productive through artificial subsurface (tile) drainage.
New drainage systems continue to be installed in Minnesota and elsewhere, largely to replace older, less functional drainage systems. The agronomic and environmental benefits of subsurface agricultural drainage are many: improved crop establishment, growth and yield; improved soil trafficability and field operations; reduced soil compaction; and reduced surface runoff, with associated reductions in sediment and phosphorus losses from poorly drained agricultural fields.
Unfortunately, several unwanted environmental effects are caused by agricultural drainage, including nitrate/nitrogen losses to surface waters (a component in Gulf of Mexico Hypoxia) and losses of temporary surface ponding that supports migratory bird habitat.
However, practitioners of agricultural drainage have never had more options for designing and managing subsurface drainage systems to incorporate both productivity and water quality goals.
Extension engineers and soil scientists at the University of Minnesota are in the process of reevaluating the drainage benefits and water quality impacts for the poorly drained soils of Minnesota. They plan to have new design tables and online tools available in early 2011.
The annual Extension Drainage and Water Management workshops have emphasized alternative approaches to drainage design and management for the past few years. Contractors, designers, and agricultural producers are encouraged to consider new approaches to system layout and selection of design, including water removal rates, for every new drainage project.
Managed drainage--sometimes called "controlled drainage"--provides an opportunity to manage water table depths in a drained field, in contrast with a traditional drainage system that functions to maintain water table depths at or below the tile depth. More details are on the Extension website at www.extension.umn.edu/go/1033.
When higher water tables can be sustained, opportunities to reduce drainage volumes and nitrate losses by 10 to 30 percent materialize, without negatively impacting crop yield. A recent field study in southwest Minnesota showed that for a Millington soil, average drainage volume was reduced by 61 percent, and nitrate and total phosphorus losses by 61 and 50 percent, respectively.
Information on other alternatives for drainage water management systems can be found on Extension's "Drainage Outlet" website, www.extension.umn.edu/DrainageOutlet.
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Gary Sands is a water resources engineer with University of Minnesota Extension. Jeffrey Strock is a soil scientist and assistant professor with the University of Minnesota Southwest Research and Outreach Center and Department of Soil, Water, and Climate.
Media Contact: Catherine Dehdashti, U of M Extension, (612) 625-0237, email@example.com