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Iowa Nutrient Reduction Strategy to reduce nitrogen, phosphorus loads in water here and at Gulf

By Jean Caspers-Simmet

Date Modified: 03/05/2013 9:02 AM

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MASON CITY, Iowa —Meeting the Gulf Hypoxia Task Force goal of reducing nitrogen and phosphorus loads to the Gulf by 45 percent won't be easy, but it is possible, said Matt Helmers, an ag and biosystems engineering professor at Iowa State University.

Achieving the water quality goal will take a combination of practices, Helmers said during a presentation on the Iowa Nutrient Reduction Strategy at the recent Crop Advantage Conference at North Iowa Area Community College. The strategy was released in November by Iowa Gov. Terry Branstad and Iowa Secretary of Agriculture Bill Northey.

The ag department, the DNR and ISU worked for two years to develop the strategy that was requested by the Environmental Protection Agency.

Research shows that Iowa contributes 10 percent to 17 percent of nitrogen and 5 percent to 10 percent of phosphorus delivery to the Gulf of Mexico, Helmers said.

The strategy is a voluntary, science-based program to reduce nitrogen and phosphorus impact on water, Helmers said. Cities, industry and agriculture worked on the document.

The group established a baseline of existing conditions by dividing Iowa into 10 Major Land Resource Areas. They assessed potential performance of practices and estimated the load reductions of ag and conservation practices and cost of implementation.

The average estimated nitrogen application rate for Iowa was calculated to be 151 pounds per acre for a corn-soybean rotation and 201 pounds per acre for continuous corn.

Average soil test phosphorus concentrations were calculated for each area of the state based on soil samples sent to the ISU soil lab. Optimum level is 20 milligrams of P per kilogram of soil. Average soil test P ranged from 11 in the southeast to 30 in north central Iowa.

"There are few practices that have meaningful impact on reducing both N and P because the nutrients have different modes of transportation," Helmers said.

The maximum return to nitrogen rate calculator is a tool to calculate the optimal amount of nitrogen to apply based on corn and nitrogen fertilizer prices, Helmers said. It also reports a range around the optimum. The science team used $5 per bushel corn and 50 cent per pound nitrogen prices to estimate recommended fertilizer rates of 123 to 147 pounds per acre.

Since wastewater treatment plants and industrial facilities would achieve the maximum biological removal rate of 4 percent N and 16 percent P, the non-point source, or agricultural goal, becomes 41 percent N and 29 percent P to achieve the 45 percent goal, Helmers said.

In one scenario designed to meet N and P goals, all farmers use optimum nitrogen rates, cover crops are on 60 percent of row crop acres, 27 percent of ag land is treated with a wetland and 60 percent of drained land runs through bioreactors.

A second scenario involves optimum nitrogen rates, cover crops on 95 percent of acres, 34 percent of the most intensive row crop areas treated with wetlands and 5 percent crop land retirement.

In a third scenario all farmers use optimum nitrogen rates, nitrogen inhibitors with all fall applied commercial N, and they sidedress all spring nitrogen. Seventy percent of tile drained areas are treated with bioreactors, 70 percent of all applicable land has controlled drainage, 31.5 percent of ag land is treated with a wetland and 70 percent of all agricultural streams have buffers. There would be P rate reduction on all ag land, 90 percent of conventionally tilled corn and soybean and continuous corn acres would be converted to conservation tillage and 10 percent of non-no-till to no-till.