New Report Says Iowa’s Conservation Investments Make a Difference in Water Quality

Catherine Kling;
Hongli Feng;
Philip Gassman;

November 9, 2007

How have existing on-farm conservation efforts affected Iowa's water quality and what value do they have?

Seven major conservation practices used on Iowa farms 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 that otherwise would be present in 13 large-scale watersheds that cover most of the state. Those are the findings from a new report prepared by researchers at Iowa State University's Center for Agricultural and Rural Development (CARD). The study estimates that Iowans invest about $435 million annually in these agricultural conservation practices.

The complete study findings are contained in "Conservation Practices in Iowa: Historical Investments, Water Quality and Gaps," which takes a detailed look at the cumulative costs and environmental benefits of conservation practices on Iowa farms.

The research and analysis were conducted by a team of researchers from CARD, with funding provided by the Leopold Center for Sustainable Agriculture, Iowa Farm Bureau Federation, Iowa Soybean Association and the Iowa Corn Growers Association.

The study was designed to help provide a benchmark for current conservation practices to help establish viable solutions for future conservation efforts. Specifically, it sought to answer three questions:

  • What is the value of major conservation practices currently in place on Iowa farms?
  • What are the effects of these practices on water quality?
  • What would it take to improve water quality to obtain specific standards?

The estimated $435 million investment includes average statewide costs of about $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, which is based on 2004 coverage and costs.

To answer the second question on 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. 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.

To answer the third question, 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, 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.

"This study does not provide a single solution on how to improve Iowa's water quality," said Catherine Kling, head of CARD's Resource and Environmental Policy Division and lead researcher in the study. "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 use options. 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."

Jeri Neal, who leads the Leopold Center's ecological systems research initiative, agreed that 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," she said. "The models show we also can get a lot more, but that it's going to take a lot more dollars. 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