Agricultural Drainage

Bulletin 871-98

Minnesota

Highlights

• A Technical Forum on the hydrologic impacts of drainage has been developed by the University of Minnesota and scientists within federal and state agencies, and universities. The goals of the Technical Forum include establishing a dialogue among scientists to enable a better understanding of the effects of drainage on the hydrology of watersheds. A particular concern in areas of the Midwest is the degree to which agricultural drainage contributes to flooding. Presentations suggested that:
  • Precipitation is the factor responsible for most of the variation in large-river flows including flows associated with Minnesota's most extreme floods;

  • The floods of 1993 and 1997 occurred in the context of a long-term increase in average annual precipitation which began in 1940;

  • The impact of drainage is difficult to quantify, but it appears to be less important for extreme floods of major basins such as those that occurred in 1993 in the Minnesota River Valley, and in 1997 in the Red River Valley; and

  • It is important to ensure that adequate drainage capacity exists before drainage system expansion. Some areas of Minnesota have experienced an overload on existing drainage outlets.

  Future dialogues of the Technical Forum will be expanded to explore impacts of agricultural drainage on water quality.

• South-central Minnesota's landscape consists mainly of flat agricultural fields with numerous small depressions. These depressions typically consist of poorly-drained soils and require some type of modification to remove excess water. A widely used method is installation of a surface drainage inlet, usually a vertical pipe that connects the land surface to a subsurface drainage system allowing water to drain quickly out of the depression. The cumulative hydrologic and water quality impacts of these inlets are being evaluated with the hydrologic and sedimentologic model called DROPLETS (Drainage Response Of Pothole Landscapes and the Erosion and Transport of Sediment). In DROPLETS, complex watersheds are broken down into simpler, idealized landscapes. The response of these landscapes are simulated and then combined to simulate the overall response of the watershed.

• Herbicide loss in subsurface drainage from agricultural land is not well understood. Research was conducted to assess atrazine and alachlor losses in subsurface drainage during and after long-term use on Webster clay loam soil at Waseca under typical agricultural management conditions. Annual alachlor and atrazine use was initiated in 1974 and 1975, respectively. Alachlor use was continued through 1991 while atrazine use was terminated after the 1988 application. Subsurface drainage water was collected and analyzed for atrazine and alachlor beginning in October 1985. Alachlor was detected in only 2% of the samples from 1985 through 1991. Atrazine or a degradation product that analyzes as atrazine was detected in 97% of the samples from 1985 through 1990. There was little fluctuation in atrazine concentration during any year. Tillage systems had minimal impacts on atrazine concentrations in drainage waters. Low concentrations of atrazine may be detected in subsurface drainage water during and after long-term use, and may persist for several years after use is stopped. Concentrations of alachlor in drainage waters from these high organic matter, fine-textured soils appears to be minimal.

• Soil compaction by heavy agricultural equipment is a serious problem on wet agricultural soils. Although compaction caused during tillage and harvesting can sometimes be reduced by the natural processes of freezing-thawing and wetting-drying, compaction on many soils in Minnesota may be getting worse, and there is no evidence that these natural agents have a large-scale effect. Compaction research conducted by the USDA and University of Minnesota is providing new insight into how soil water content affects the potential for soil compaction. This research points to the benefits of subsurface drainage to reduce compaction, and furthermore the need to maintain existing drainage systems.

Northern Cornbelt Sand Plain Management Systems Evaluation Area (MSEA)

The goal of the Northern Cornbelt Sand Plain MSEA is to evaluate the impact of ridge-tillage and various combinations of chemical management on ground water beneath a corn-soybean cropping system. Research and educational activities are headquartered in Minnesota and extend to three sand plain regions in North Dakota, South Dakota, and Wisconsin. The main research site in Minnesota is located about 55 miles northwest of the Twin Cities in Sherburne County near Princeton. The 160-acre site is situated on the Anoka Sand Plain, which covers an area of about 1,700 square miles in east-central Minnesota. The Anoka Sand Plain is characterized by extremely porous sandy soils, shallow depth to the water table (12 ft at the site), flat topography and low runoff.

Elevated concentrations of nitrate, chloride, and the triazine group of herbicides (i.e., atrazine) have been detected in the ground water of irrigated areas of the Anoka Sand Plain. Much of this ground water recharges into streams which eventually empty into the Mississippi River, a major source of drinking water for the Twin Cities metro area. Analysis of more than 2,600 water samples at Princeton, MN show that, with careful management, corn and soybean can be grown on sandy soils without exceeding EPA drinking water standards. Atrazine was detected only occasionally and concentrations were less than 1 micro-g/L (1 micro-g/L equals 1 ppb). The EPA drinking water standard is 3 micro-g/L. Nitrate-N concentrations ranged between 10 and 20 mg/L, which were only slightly higher than background concentrations.

Educational opportunities have increased in recent years with
producers interested in improving existing drained fields, and others
concerned about increased flooding in major river valleys. Extension
specialists and researchers from the University of Minnesota have
responded through increased educational programs at county cluster
meetings, station field days, and a newly initiated annual farmland
drainage design workshop.