Guest contributor Cathy Kling (Iowa State University) provides a summary of her recent research (with many colleagues) on the costs and water quality improvements from adoption of agricultural conservation practices.
Estimating the costs and water quality improvements from broad adoption of conservation practices in agriculture.
Authors: Silvia Secchi, Philip W. Gassman, Manoj Jha, Lyubov Kurkalova, Hongli Feng, Todd Campbell, and Catherine Kling
Affiliation: Center for Agricultural and Rural Development, Iowa State University
Water pollution from nonpoint sources, the diffuse runoff from farms and other areas, represents a large and pervasive portion of many state’s water quality problems. This new research, funded in part by the Iowa Department of Natural Resources, is a first step in a more comprehensive assessment of Iowa’s options.
The approach combines economic models and data on land use and conservation practices with a physical-based model, the Soil and Water Assessment Tool, that predicts stream flow, sediment, and nutrient loads (phosphorous and nitrogen) for 13 watersheds in Iowa based on selected conservation practices. The practices and rules for placing them on the landscape were devised in conjunction with the Iowa DNR to target sediment and phosphorous problems and included such practices as grassed waterways, terracing, contouring, conservation tillage, land set-asides (such the Conservation Reserve Program), and nutrient management strategies.
The annual costs of the conservation practices ranged from about $300 million to $320 million. Land set-aside and conservation tillage were found to be the most costly practices (with terracing costs spread out over 25 years). The environmental effects of the practices varied among the watersheds. Sediment decreases ranged from 6 percent in the Little Sioux River Watershed to 65 percent in the Turkey River Watershed. The majority of the watersheds had a predicted decrease in phosphorous of over 40 percent, and nitrate reductions ranged from 6 to 20 percent.
It is important to note that the set of practices chosen are not likely to be the most cost-effective methods and/or locations. Further, a number of oversimplifying assumptions were necessary for this first pass and it is not clear that this set of practices improves water quality to the point that society feels is appropriate. Thus, while the specific numbers from this study should be viewed as suggestive only, the method and approach appears to hold significant promise for guiding policy.
A short report, “The Cost of Clean Water: Assessing Agricultural Pollution Reduction at the Watershed Scale,” is available here.
