KANAWHA —Agriculture must be proactive in implementing practices to reduce the amount of nitrogen and phosphorous leaving fields, said Matt Helmers, Iowa State University Extension agricultural engineer.
Helmers talked about Iowa's Nutrient Reduction Strategy and practices farmers can use to reach the Hypoxia Action Plan goal of 45 percent reduction in nitrogen and phosphorus going down the Mississippi River. In Iowa's strategy, point and non-point sources work together to achieve the goal. Agriculture is asked to reduce nitrate by 41 percent and phosphorus by 29 percent.
"The demand for clean water is not going to go away," Helmers said at last week's field day at ISU's Northern Research Farm at Kanawha. "The alternative to a voluntary approach is regulation."
Helmers shared research from Gilmore City that studied the effects of nitrogen and herbicide management practices on the quality of tile drainage since 1990.
"This site has been important for understanding nutrient movement in the tile-drained landscape and is one of the longest running, continuously active drainage research sites in the country," Helmers said.
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The study has looked at commercial fertilizer, swine manure and, more recently, urea and poly-coated urea. Cover crops and perennial forages' ability to reduce nitrate loss also have been examined.
Researchers found that when nitrogen fertilizer is applied at economic rates, the average concentration of nitrate nitrogen in tile drainage ranged from 12 to 16 milligrams per liter, Helmers said. The drinking water standard is 10 milligrams.
When similar nitrogen application rates to corn are used in a corn-soybean rotation or in a continuous corn rotation, similar nitrate concentrations are observed in tile drainage. When an additional 50 pounds of nitrogen per acre are applied to continuous corn, nitrate concentrations are about 25 percent greater than from the corn-soybean system.
Although spring application of nitrogen would be the preferred timing, during the nine years that timing of fertilizer applied was studied, there was little difference in the concentration or loss of nitrate-nitrogen between spring- and fall-applied.
Cover crops have the potential to reduce nitrate-nitrogen concentrations in drainage water, and perennial land use has the potential to dramatically reduce nitrate-nitrogen concentrations in drainage water.
"The research has shown that nitrate-nitrogen concentration generally exceeded 10 mg/L under a corn-soybean rotation when fertilized at common rates," Helmers said. "Even when no fertilizer is applied, there is loss of nitrate-nitrogen. Based on these studies, high nitrate levels are less about mismanagement of nitrogen fertilizer and more a result of land use and cropping practices."
Helmers said nitrogen management is essential, but it will only get farmers part of the way to the 41 percent nitrate reduction goal. They also need to consider practices such as cover crops, controlled drainage, buffers, saturated buffers, and bioreactors and wetlands that intercept tile water and treat nitrates.
Many of these practices provide additional benefits such as soil quality, erosion control and wildlife habitat, Helmers said.
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The Legislature appropriated money this session to get more of these practices on the landscape and federal initiatives are also availablel, Helmers said.
"Think about what practices you might want to demonstrate on your land," he said.
