November / December, 2001

Water Table Management to
Enhance Water Quality and Farm Profit

By: H. W. Belcher

Michigan agricultural producers have many years experience controlling their subsurface drainage to enhance crop production. Much of the most productive crop land in Michigan has a naturally occurring shallow water table and relatively flat topography. To be productive those soils were artificially drained decades ago using underground pipes - first clay and concrete and more recently corrugated plastic tubing.

Figure 1. Drainage plow installing corrugated plastic tubing.

In the Saginaw Bay area, where the water level in outlet ditches is controlled by Lake Huron, drainage pumps are often required to discharge the drainage water. A few innovative farmers tried turning their pumps off after spring field work and then leaving them off through much of the summer. They often observed increased crop yield along with savings on their electric bill. A few of those farmers began experimenting with using their pumps to add water to the subsurface drainage systems during dry growing seasons. Pumping water into the drain pipes seemed to further increase crop yield.

A good idea has a way of getting out. In the early 80's Michigan producers began asking MSU agricultural engineers questions about using subsurface drainage systems for both drainage and irrigation. Responding to a growing interest, a multi-disciplinary team of engineers, soil scientists, agronomists, crop modelers, economists, farmers and drainage contractors was assembled and began planning applied research projects that would provide answers to the questions being asked. The research that resulted was designed to address the questions:

• does subirrigation work;
• what are the conditions for successful subirrigation;
• how should systems be designed and installed that are used for both drainage and irrigation;
• how should those systems be operated;
• what are the costs and benefits associated with subirrigation; and

Research and Demonstration

The answers began coming from field scale research initiated in 1984. That research started on a University owned production agriculture field and was followed by research on farmer owned fields located near Bannister, St. Johns and Unionville. Next came the 1986 Saginaw Bay Subirrigation / Drainage Project, a USDA project that funded 26 studies directly addressing questions concerning the economic, environmental, engineering and sociological opportunities and challenges associated with water table management expansion within five Saginaw Bay Counties - Bay, Huron, Saginaw, Sanilac and Tuscola. The Saginaw Bay work led to a 10 year project (starting in 1991)on a privately owned field near Saginaw. The Saginaw site allowed replicated, multi-disciplinary data collection and included facilities to limit rain on intensively instrumented plots and to observe growing roots. How does subirrigation effect the edge of field surface and subsurface water quality?

Figure 2. Rain controlled intensive plots at Saginaw site.

Research Highlights

• Water Quality

  • At Bannister, for 20 months of monitoring beginning in 1987, the total dissolved nitrate-N delivered from the Bannister field to the outlet ditch by the subsurface drainage system was reduced 64% by subirrigating.

  • At Unionville, for two growing season, water table management by subirrigation reduced dissolved nitrate-N leaving the field by 58% and dissolved orthophosphate-phosphorus by 16% compared to conventional subsurface drainage. The total drainage volume, surface and subsurface, was 17% greater for subirrigation than for conventional subsurface drainage. However, subirrigation increased the volume of surface drainage by only 7%.

• Yield/Economics - Side-by-side comparison of subirrigated to conventional subsurface drained crop yields during 1985 through 1995 showed:

  • The average of 24 yield observations made at numerous locations in the south half of the lower peninsula was 173 bu/ac. Eight subirrigated soybean yield observations averaged 53 bu/ac and five subirrigated sugar beet observations averaged 22 t/ac.

  • Comparison yields measured from adjacent subsurface drained fields without subirrigation averaged 138 bu/ac for 16 corn yield observations, 37 bu/ac for two soybean yield observations and 22 t/ac for five sugar beet yield observations.

  • The yield results suggest that for field crops, at present market value, subirrigation provides a positive return on investment until the capital cost of subirrigation improvement exceeds about $600/ac more than the cost of a conventional subsurface drainage system; and

  • The cost of water table management by subirrigation is less than other irrigation methods both in terms of capital cost and operation cost for cropland that requires subsurface drainage.

Figure 3. Water table depth control structure during subirrigation

In General

• For a substantial percentage of Michigan cropland, water table management by subirrigation is feasible and often provides both water quality and economic benefit
• Water table management systems must be properly designed and operated to achieve potential benefits. Poorly designed and/or operated water table management systems waste water and energy, increase discharge of nutrients and pesticides, and reduce yields.
• Michigan farmers with subsurface drainage systems that need to be upgraded should consider modifying those systems to allow water table management by subirrigation.

For more information

Contact Dr. Belcher at (517) 353-5270, email: belcher@egr.msu.edu.
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Agricultural Engineering
Michigan State University
A.W. Farrall Hall
East Lansing, MI 48824-1323
(517) 355-4720

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