Study shows diversity needed in tackling Iowa water quality issues

While no one expected to find a “silver bullet” that would solve Iowa’s water quality problems, an 18-month study about on-farm conservation practices added some defining numbers to the discussion and reinforced several assumptions.

The Leopold Center partnered with the Iowa Farm Bureau Federation, Iowa Soybean Association and the Iowa Corn Growers Association to assemble a broad view of the cumulative costs and environmental benefits of conservation practices on Iowa farms. The results are contained in a new report, “Conservation Practices in Iowa: Historical Investments, Water Quality and Gaps,” prepared by a team of researchers from Iowa State University’s Center for Agricultural and Rural Development (CARD).”

Findings in a nutshell
Researchers used modeling to identify seven conservation practices that contributed the most to nutrient reductions in 13 watersheds in the state. Depending on the watershed, these practices are estimated to remove 11 to 38 percent of the total nitrogen, 6 to 28 percent of the nitrate and 25 to 58 percent of the phosphorus, and altogether are valued at about $435 million each year.

Jeri Neal, who leads the Leopold Center’s ecological systems research initiative, said the project was designed to provide a benchmark for current conservation practices to help establish viable solutions for future conservation efforts.

“We are impressed with these baseline numbers as an indicator of how much Iowans invest in conservation practices because clearly, Iowans care,” she said. “The models show we also can improve a lot more, but that it’s going to take a lot more dollars. So from the Leopold perspective, it’s important that we work past single solutions for ways to produce maximum ecological and economic benefits - yield plus, if you will.”

The estimated $435 million annual investment includes average statewide costs of close to $37 million for selected Iowa conservation structures (terraces and grassed waterways), annual payments of about $175 million to farmers for acres set aside as part of the Conservation Reserve Program, plus contour farming, contour strip cropping, no-till and mulch-till conservation practices in farming operations. The data sets used in the analysis represent conservation practices and their costs in place in 1997, except for conservation tillage, based on 2004 coverage and costs.

“Our results indicate that the most cost-effective measures to improve water quality are different across different watersheds, and that targeting different pollutants will mean different land us

e options,” said Catherine Kling, head of CARD’s Resource and Environmental Policy Division and lead researcher in the study. “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.”

To determine the effectiveness of these practices, CARD researchers relied on a widely used water quality model, the Soil and Water Assessment Tool (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. Nitrate loadings in the western Iowa watersheds were reduced by the greatest amount.

To look at costs for future improvements, researchers considered three scenarios using the SWAT model: to reduce phosphorus loadings by 40 percent, to reduce nitrate loading by 25 percent, and to reduce both phosphorus and nitrate by 40 percent and 25 percent, respectively.

They looked at a variety of land use options – from land retirement to conservation tillage and fertilizer reduction – and used computational tools known as evolutionary algorithms to search for the lowest costs of reaching targets in each scenario. The options did not include longer or more varied crop rotations, or the use of buffers or manure in place of fertilizer inputs.

According to the model outputs, a scenario that would target a 40 percent reduction for phosphorus would simultaneously result in a 31 percent reduction in nitrate loadings. However, the annual estimated cost to implement a variety of conservation practices would be $613 million statewide. These costs are in addition to funding existing conservation practices.