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Developing a Science Assessment for Wisconsin’s Nutrient Reduction Strategy
The Ag Water Quality Program and UW-Madison staff have developed a Science Assessment to accompany Wisconsin’s Nutrient Loss Reduction Strategy. This assessment quantifies the effectiveness of different agricultural management practices in reducing nutrient losses from farm fields to Wisconsin’s waterways. Initially, the team’s efforts focused on phosphorus losses to surface water and will ultimately expand to consider nitrogen losses to groundwater and surface water.
This effort built on lessons learned from recent science assessments that have been conducted by neighboring states, namely Iowa and Minnesota. A key take-away from these assessments was that many conservation practices had highly variable effects on nutrient losses. Overall, the reported variability for some practices was so high that little conclusion could be drawn about their effectiveness in improving water quality.
Building on these results, the Wisconsin Science Assessment first uses SNAPPlus and the Wisconsin P Index model (>170,000 unique field-scale scenarios were simulated) to understand if and how implementing different conservation practices reduces phosphorus (P) losses relative to specified “baseline” practices across contrasting soil and climate regions in our state. The P Index model was run under a wide range of different management scenarios relevant to grain and forage cropping systems. For example, scenarios compared differences in P form (fertilizer or liquid dairy manure), rate and timing of application, soil-test P, tillage, cover crop, and presence of a filter strip, among other factors. Comparisons were made across soil types and within and among different cropping systems, providing context to better understand in what cases particular practices were more or less effective in decreasing P losses.
Second, to provide context and targeted assessment of additional management practices, we synthesized and analyzed measurements of surface P runoff data collected from the WI Discovery Farms program and discussed findings from related WI case studies published in peer-reviewed scientific literature.
For reducing total P losses, four practices were particularly effective: decreasing tillage intensity, adding edge-of-field filter strips, incorporating perennial or overwintering crops, and early establishment of cereal rye cover crops. Shifting from intensive tillage to no-till consistently offers high P reduction, even on soils with high soil test P. Case studies emphasize that grassed waterways can significantly decrease total P losses in erosion-vulnerable fields, and avoiding winter manure application reduces the risk of P runoff. While most strategies target soil-bound P, long-term soil-test P drawdown through decreased P fertilizer application is uniquely effective at reducing dissolved P losses. Overall, this study highlights the potential benefits of controlling total P losses through a combination of in-field practices (tillage reduction and early planted cover crops), structural practices (filter strips and grass waterways), and cropping-systems changes (adding overwintering or perennial crops) in the most vulnerable fields.
Process and Timeline
An advisory committee of 14 UW-Madison faculty and staff with relevant expertise met to discuss and direct the project, and a subset of this team focused on the detailed work of compiling synthesizing relevant research studies and datasets. With the completed report, Assessing practices to decrease agricultural phosphorus losses in Wisconsin, the Agriculture Water Quality Program staff will lead outreach efforts across the state.
As of September 2026, some materials are now available online and additional resources are being developed with feedback from users and interested stakeholders. As outreach efforts continue, regional toolkits and tailored outreach materials will be developed based on feedback and needs identified.
Faculty and Staff
UW-Madison faculty and staff team members include:
- Steven Hall, Co-Faculty Advisor, Discovery Farms
- Amber Radatz, Program Manager, Ag Water Quality Program
- Ellen Albright, Researcher, Discovery Farms
- Francisco Arriaga, Soil and Water Conservation Management Extension Specialist and Associate Professor, Department of Soil Science
- Hava Blair, Researcher, Department of Soil Science
- Eric Booth, Associate Scientist, Departments of Agronomy, and Civil and Environmental Engineering
- Jeff Hadacheck, Assistant Professor, Department of Agricultural and Applied Economics
- Margaret Kalcic, Associate Professor, Department of Biological Systems Engineering
- Chris Kurcharik, Professor, Wisconsin Energy Institute, Departments of Atmospheric and Oceanic Sciences, Agroecology, and Freshwater and Marine Science
- Kevin Masarik, Groundwater Education Specialist, Extension and UW-Stevens Point
- Mallika Nocco, Agrohydrology Extension Specialist and Assistant Professor, Department of Biological Systems Engineering
- Natasha Rayne, Extension Specialist and Assistant Professor, Department of Soil Science
- Matt Ruark, Co-Faculty Advisor, Discovery Farms
- Laura Ward Good, Scientist, Department of Soil Science
References
Testing the Wisconsin Phosphorus Index with Year Round, Field Scale Runoff Monitoring