Margaret M. Kalcic

Use of nutrient management practices to reduce nutrient loss from agriculture and its associated water quality consequences, including hypoxia and eutrophication, is widely encouraged. However, little is known about which factors influence farmers’ risk perceptions associated with nutrient loss, and thus possibly influence their decisions to adopt such practices. To determine which factors were associated with relative “accuracy” of nutrient loss–associated risk perceptions, specific farm field management information was used as inputs to a Soil and Water Assessment Tool model of the study watershed to produce water quality outputs for each modeled farm field. This information was paired with farmers’ risk perceptions associated with nutrient loss on their farm to assess relative “accuracy” of each farmer’s perceptions compared to the rest of the farmers in the study. We then investigated characteristics of the farm and farmer that are associated with comparative “overprediction” and “underprediction” of risk, and found that characteristics of the individual (conservation identity, prior conservation practice adoption, efficacy beliefs, and perceived seriousness of the consequences of nutrient loss) are more important in determining whether farmers are likely to “overpredict” or “underpredict” risk than is the objective (modeled) vulnerability of their land to nutrient loss.

We develop the first spatially integrated economic-hydrologic model of the western Lake Erie basin explicitly linking economic models of farmers’ field-level best management practice (BMP) adoption choices with the Soil and Water Assessment Tool to evaluate nutrient management policy cost-effectiveness. We quantify trade-offs among phosphorus reduction policies and find that a hybrid policy coupling a fertilizer tax with cost-share payments for subsurface placement is the most cost-effective and can achieve the policy goal of 40% reduction in nutrient loadings. We also find economic adoption models alone can overstate the potential for BMPs to reduce nutrient loadings by ignoring biophysical complexities. (JEL Q18, Q53)

Several structural, treatment, and management approaches exist to minimize phosphorus (P) transport from agricultural landscapes (e.g., cover cropping and conservation tillage). However, many of these practices are designed to minimize particulate P transport and are not as effective in controlling dissolved P (DP) losses. Phosphorus removal structures employ a P sorption material (PSM) to trap DP from flowing water. These structures have been successful in treating surface runoff by utilizing aluminum (Al)-treated steel slag, but subsurface tile drainage has never been tested with this material. The goal of this study was to evaluate the performance and economics of a ditch-style P removal structure using Al-treated steel slag for treating agricultural subsurface drainage discharge. The structure treated subsurface drainage water from a 4.5 ha agricultural field with elevated soil test P levels. Overall, the structure removed approximately 27% and 50% of all DP and total P (TP) entering the structure, respectively (i.e., 2.4 and 9.4 kg DP and TP removal). After an initial period of strong DP removal, the discrete DP removal became highly variable. Flow-through analysis of slag samples showed that the slag used to construct the structure was coarser and less sorptive compared to the slag samples collected prior to construction that were used to design and size the structure. Results of this study highlight the importance of correctly designing the P removal structures using representative PSMs.