Drainage fact sheet
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Minnesota has more than 21,000 miles of ditches and channelized streams (shown in red, above: source, DNR), which serve as the drainage infrastructure for the agricultural reguions of Minnesota. Meeting water quality drainage needs for agriculture is a current priority.
- Surface drainage (ditches) and subsurface (tile) drainage are the primary artificial drainage practices.
- Subsurface (tile) drainage began in upstate New York in 1830's (Johnston Farm).
- Glacial processes in upper Midwest created an abundance of highly productive but poorly drained soils (inset).
- Approximately 25% of United States arable land employs one/both surface and subsurface drainage.
- Earliest drainage activities in the upper Midwest addressed agriculture, transportation infrastructure, and human health needs.
- Percentage of tile-drained land in Minnesota varies widely, but perhaps 20-30% of the agricultural soils in the Minnesota River Basin are tile-drained. In some locations, higher percentages exist.
- Farmers in Minnesota are permitted to drain their lands provided they have an outlet and comply with USDA and State wetland regulations.
- Current drainage activity in the Midwest typically replaces older, less effective drainage systems with new systems. Incorporating technologies to reduce environmental concerns in these new systems is important.
Drainage benefits and impacts
Jonathan Chapman Extensive research is underway exploring opportunities to mitigate unwanted environmental effects while maintaining agricultural productivity
- Poorly drained soils increase risks to agricultural production from excess water and high water tables.
- Proper soil drainage improves agricultural production by ensuring timely planting and field operations, minimizing soil compaction and buildup of salts, promoting conditions for good seedbed establishment and germination, and minimizing high water table stresses to growing crops. Well drained soils out-yield poorly drained soils and have less year-to-year yield variability.
- Proper soil drainage also improves the opportunity to employ other conservation practices such as minimum tillage.
- Both artificial drainage and land-use change (prairie to agriculture) affect hydrology, water quality and habitat. The individual effects of drainage and land-use change are difficult to separate.
- Surface and subsurface drainage have very different hydrologic impacts:
- Surface drainage speeds flow from landscape and increases peak flows.
- Tile drainage promotes more infiltration, slowing water delivery from the landscape (compared to surface drainage), but studies indicate potential for overall increases in water yield from 5 to 10%.
- Local hydrologic effects are dampened at larger watershed scales.
- Surface and subsurface drainage affect water quality differently:
- Surface drainage may increase losses from surface runoff (sediment and phosphorus, primarily).
- Tile drainage may reduce surface runoff pollutants but may increase dissolved nutrients, such as nitrate.
- Drainage activities have reduced the number and extent of wetlands, in some areas by as much as 90%, but wetlands are now protected by Federal and State laws. In some areas, wetlands are actually being restored, usually on land that once was cultivated.
"Conservation drainage" practices include:
- Nutrient BMP's
- Controlled drainage or "drainage water management"
- Two-stage ditches
- Shallow drainage
- Reduce drainage intensity
- Woodchip bioreactors
- Improved surface inlets
- Improved side inlets
- Winter cover crops
- Wetland restoration
- Nutrient retention basins
Drainage water management
Drainage water management design (below left) calls for dividing the field into water control/management zones, aligning laterals with the field contours, and using control structures. Annual subsurface flow and nitrate reductions from 10 to 50% may be possible.
Extensive research is underway exploring opportunities to mitigate unwanted environmental effects while maintaining agricultural productivity
R. Cooke, University of Illinois
Water control structures enable shallower water tables to be achieved, conserving water and nutrients in the soil profile.
Further reading and information
- Blann, K., J.L. Anderson, G. Sands, B. Vondracek. 2009. Effects of agricultural drainage on aquatic ecosystems: A Review. Critical Reviews in Environmental Science and Technology 39(11):909-1001.
- Frankenberger, J., E. Kladivko, G. Sands, D. Jaynes, N. Fausey, M. Helmers, R. Cooke, J. Strock, K. Nelson, L. Brown. 2006. Drainage water management for the Midwest: Questions and answers about drainage water management for the Midwest. Purdue Extension Publication WQ-44.
- Skaggs, R. W., M. A. Breve, and J. W. Gilliam. 1994. Hydrologic and water quality impacts of agricultural drainage. Critical Reviews in Environmental Science and Technology 24: 1-32.
- Moore, I.D. and C. Larson. 1979. Effects of drainage projects on surface runoff from small depressional watersheds in the north central region, WRRC Bulletin 99.
- Robinson, M. and D. Rycroft. 1999. The impact of drainage on stream flows. In Agricultural Drainage. ASA-SSSA-CSSA Monograph 38: 767-800.
- Sands, G.R., I. Song, L.M. Busman, B. Hansen. 2008. The effects of subsurface drainage depth and intensity on nitrate load in a cold climate. Trans. of the ASABE 51(3):937-946.
- Dinnes, D. L., D.L. Karlen, D.B. Jaynes, T.C. Kaspar, J.L. Hatfield, T.S. Colvin, C.A. Cambardella. 2002. Nitrogen management strategies to reduce nitrate leaching in tile drained Midwestern soils. Agron. J. 94(1) 53-171.
- Skaggs, R. W., M. A. Youssef, G. M. Chescheir, and J. W. Gilliam. 2005. Effects of drainage intensity on nitrate losses from drained lands. Trans. of the ASABE 48(6): 2169-2177.
- Thorp, K. R., D. B. Jaynes, R. W. Malone. 2008. Simulating the long-term performance of drainage water management across the Midwestern United States. Trans. of the ASABE 51(3): 961-976.