Although the percentage of cropland drained in Minnesota is lower than other Midwestern states, the 1985 National Resource Inventory estimate for total cropland acres drained (6,370,000) is significant. The state boasts a rich history of drainage related hydrologic and water quality research and educational activities.
Key drainage and water quality research results are summarized in the following points: 1) the amount of growing season rainfall and the distribution of rainfall during the year greatly affects drainage volume, nitrate-N concentrations, and nitrate-N losses; 2) nitrate losses from the landscape are highly related to cropping system; 3) nitrate-N losses to subsurface drainage are greatly influenced by rate of nitrogen application and moderately influenced by time of nitrogen application; 4) the placement method of nitrogen and tillage have minimal effects on nitrate losses in drainage; and 5) best management practices (BMPs) used by farmers reduce nitrate losses to subsurface drainage. However, mineralization of high organic matter soils still contributes significantly to nitrate losses.
To address agricultural issues related to increased flooding in recent years, Extension specialists and researchers are providing research-based information on design criteria, economic feasibility and environmental impacts of agricultural drainage to producers, drainage contractors, landowners, soil and water resource planners, and others.
National Resource Inventory data from 1985 indicated that 20% of Minnesota's cropland had undergone surface or subsurface drainage improvements. Anecdotal evidence suggests that an even higher percentage of cropland is actually drained.