FO-03875 Reviewed 2008
Most of the irrigated acreage in Minnesota consists of highly permeable, low water holding capacity, sandy textured soils overlying surficial (shallow) and buried sand and gravel aquifers. Figure 1 locates most of these aquifers in the state's glacial outwash sand plains. Most homeowners and farmers in these areas get their drinking water as well as livestock and irrigation water from these aquifers.
If not properly managed, the surficial aquifers are very susceptible to non-point water quality degradation from land use practices. These aquifers are recharged annually by snow melt and rainfall. The water table of these aquifers typically is 6-15 feet below the land surface. Some of the ground water may flow into streams and rivers while some percolates deeper recharging underlying buried aquifers.
Irrigating sandy soils requires increases in fertilizer and pesticides for most crops to produce a maximum economic (profitable) yield. Nitrogen fertilizer and certain pesticides when applied to sandy soils have the potential to move downward (leach) in the soil profile, possibly into the ground water.
The Minnesota departments of agriculture and health report that some wells (domestic and observation) in the cultivated outwash sand plains region contain elevated levels of nitrates and detectable amounts of agricultural pesticides.
This is one of the reasons that the timing and amount of irrigation water applied are crucial decisions for each operator. Applying too much water means increased pumping costs, reduced water efficiency, and increased potential for nitrates' and pesticides' leaching below the rooting zone and into the ground water. Delaying an irrigation until plant stress is evident can result in economic yield loss and, consequently, poor use of some agrichemicals. Some under utilized chemicals are then subject to even greater leaching potential after the growing season when the greatest soil recharge events from rainfall usually occur.
This publication describes some "best" soil moisture management strategies and monitoring techniques that an irrigating farmer should consider in managing irrigation water and soil moisture for optimum crop production and least possible degradation of ground water quality. Information on best nitrogen and pesticide management practices for irrigated crops is discussed in several publications of the University of Minnesota Extension Service.
The following publications related to irrigated crop production can be requested through the county offices of the University of Minnesota Extension Service or from the Extension Store, 1420 Eckles Ave., University of Minnesota, St. Paul, MN 55108.
The author expresses appreciation and thanks to the following people who reviewed and contributed suggestions for the development of this publication:
James Anderson, University of Minnesota
Wayne Anderson, Minnesota Pollution Control Agency
Fred Bergsrud, University of Minnesota
John Brach, Soil Conservation Service
George Rehm, University of Minnesota
Earl Stegman, North Dakota State University
Hal Werner, South Dakota State University
This material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under special project number 89-EWQI-1-9180.
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.