AMES, Iowa – Seven major conservation practices used on Iowa farms are estimated to remove 11 to 38 percent of the total nitrogen that otherwise would be present in 13 large watersheds that cover most of the state, according to a new report by researchers at Iowa State University’s Center for Agricultural and Rural Development, CARD.

The study also found that the same conservation practives removed an estimated six to 28 percent of the nitrates and 25 to 58 percent of the phosphorus in these watersheds.

An excess of these nutrients can be deadly to native aquatic animals and plants and encourage the growth of nuisance aquatic plants and algae.

“This study does not provide a single solution on how to improve Iowa’s water quality,” says Catherine Kling, head of CARD’s Resource and Environmental Policy Division and lead researcher in the study.

“Our results indicate the most cost-effective measures to improve water quality are different across different watersheds, and that targeting different pollutants will mean different land use options,” said Kling.

“One message for stakeholders is that they must have a good knowledge of their watersheds before adopting policies to bring about change in land use,” she said.

The seven conservation practices studied are terraces, grass waterways, contour farming, contour strip cropping, no-till and mulch-till practices and acreage set aside as part of the U.S. Department of Agriculture’s Conservation Reserve Program.

The study estimates that Iowans invest about $435 million each year in these agricultural conservation practices.

The study, “Conservation Practices in Iowa: Historical Investments, Water Quality and Gaps,” takes a detailed look at the cumulative costs and environmental benefits of conservation practices on Iowa farms.

A team of CARD economists did the analysis, with funding from the Leopold Center for Sustainable Agriculture, Iowa Farm Bureau, Iowa Soybean Association and the Iowa Corn Growers Association.

The study helps provide a benchmark for current conservation practices to help establish viable solutions for future conservation efforts.

To determine the effectiveness of these practices, CARD researchers relied on a widely-used water quality model, the Soil and Water Assessment Tool called SWAT.

They looked at 13 large-scale watersheds that cover most of Iowa, and modeled the impact of seven major conservation practices on the quality of both surface water and groundwater, measured by the predicted levels of nitrogen and phosphorus in each watershed.

The extent of the practices used, land use and environmental conditions in each watershed affected the predicted outcomes. However, the seven conservation practices were responsible for statewide nitrogen, nitrate and phosphorus reductions.

Nitrates loadings in the western Iowa watersheds were reduced by the greatest amount.

The model outputs show that a scenario targeting a 40 percent reduction for phosphorus would simultaneously result in a 31 percent reduction in nitrate loadings.

Jeri Neal, who leads the Leopold Center’s ecological systems research initiative, says the study results provide a good start for discussion. “We are impressed with these baseline numbers as an indicator of how much Iowans invest in conservation practices because clearly Iowans care.”

“The models show we also can get a lot more, but that it’s going to take a lot more dollars,” said Neal. “So from the Leopold perspective, it’s important that we really need to work past single solutions to produce maximum ecological and economic benefits – yield plus, if you will.”

The full report is on the Web at

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