Agricultural Drainage

Bulletin 871-98

Ohio

Subirrigation and Ground-Water Quality

Subirrigation is a form of water table management that provides both drainage and irrigation requirements for crops with one subsurface system. Nitrate-N and atrazine concentrations were measured in shallow ground water beneath conventional subsurface drainage and subirrigation/drainage systems for corn and soybean from 1991 to 1997 at the Northwest Branch Station of OARDC near Hoytville, Ohio. Corn and soybean grown in rotation were fall chisel-plowed followed by field cultivation in the spring. Nitrate-N concentrations in the shallow ground water at 3.3, 6.6, and 9.8 ft depths were lower when subirrigation was applied during the growing season compared to when no subirrigation was applied. This reduced concentration was seen during both the growing and non-growing seasons.

There was a 76% reduction in nitrate-N concentrations in ground water at the 9.8 ft depth (lowest depth sampled) when subirrigation was used instead of conventional drainage. The lowest concentrations were reported for subirrigation with a constant water table under both corn and soybean. Water table levels maintained at a constant level beneath growing crops resulted in a 74% greater reduction in nitrate-N than a management regime of fluctuating water table levels.

Atrazine was not detectable in most of the shallow ground-water samples. When detected, atrazine concentrations were less than 0.1 mg/L (1 mg/L equals 1 ppm).

Water Table Management Scheme

Drainage water quality beneath the following water table management schemes was tested for nitrate-N concentration: conventional subsurface drainage; subirrigation/drainage with a constant water table; and subirrigation/drainage with a fluctuating water table. Subirrigation consistently showed lower nitrate-N concentrations in drainage water compared to conventional drainage. Conventional subsurface drains were always open to allow free drainage. Subirrigation/drainage systems used to maintain a constant water table level were closed for approximately 100 days beginning in mid-June. Water was added to maintain the water table at 10 in. below the ground surface and the drains were opened as necessary to lower the water table following rainfall events.

Subirrigation/drainage systems used to maintain a fluctuating water table were also closed for approximately 100 days beginning in mid-June. Again, water was initially added to raise the water table level to 10 in. below the ground surface. A fluctuating cycle was implemented where the water table level was not raised until the water table fell to 31.5 in. below the ground surface. This cycle was repeated over the growing season.

Ohio Management Systems Evaluation Area

Ohio MSEA activities occur on research sites, demonstration farms, and in watersheds. Research sites are used to evaluate different farming systems and their impacts on water quality. Demonstration farms show how agricultural management practices can be economically profitable to farmers. Results from site studies are used to model watershed processes and develop expert systems.

Cooperation between the Ohio MSEA and the PREC water quality program in south-central Ohio was established in 1990 to monitor the impacts of agricultural management systems on productivity, profitability, and ground-water quality. Phase II of Ohio MSEA, initiated in 1994, had its scope broadened to include water table management and watershed research in northern Ohio, with more emphasis on development of decision aids and expert systems. New directions for the Ohio MSEA education component includes riparian ecosystems, agricultural water management, integration of wetlands into agricultural production systems, development of a comprehensive agricultural water management guide, and addressing the Gulf of Mexico hypoxia issue.

The Ohio MSEA is a cooperative research and educational effort supported by: Ohio Agricultural Research and Development Center and Ohio State University Extension, The Ohio State University; USDA-ARS Soil Drainage Research Unit, the USDA-Cooperative State Research, Education and Extension Service, USDA-NRCS, the U.S. Geological Survey, and U.S. EPA, in cooperation with other local, state and federal agencies.

Wetland Reservoir Subirrigation Systems

The Maumee River Watershed Demonstration Project will take five years to fully implement and evaluate. Construction began during the fall of 1994. System evaluation and monitoring will begin in 1998. The work conducted at the demonstration sites is coordinated through the Maumee Valley Resource Conservation and Development Area in Defiance County. However, there are over 50 cooperators and collaborators actively involved in the project. The project is primarily funded by USEPA/GLNPO, with support funding from the Lake Erie Protection Fund, OARDC, Ohio State University Extension, Ohio Sea Grant Program, North Central Region Water Resources Research Program, and numerous agencies and associations.

Average nitrate-N concentration (mg/L) in drainage water - Spring 1997. USDA-ARS researchers found that nitrate-N concentrations in water sampled at subsurface drain outlets during February through May 1997 were lower when subirrigation had been used during the previous growing season than when subirrigation had not been applied. The graphs above show nitrate-N concentrations in drainage water observed for each drainage treatment during the spring season of 1997. The numbers shown are the seasonal average nitrate-N concentrations for each treatment method.