Using a Spatially Explicit Approach to Assess the Contribution of Livestock Manure to Minnesota's Agricultural Nitrogen Budget

This paper presents a GIS-based, spatially explicit modeling approach to assess the contribution of livestock manure to Minnesota’s agricultural nitrogen (N) budget and the associated risk of nutrient over-application. By integrating detailed feedlot data, crop rotation records, and nitrogen application guidelines, the authors estimate manure-N generation, account for storage and application losses, and model field-level manure application using varying nitrogen rates and hauling distance scenarios. Results indicate that, under guideline-recommended rates, statewide manure alone seldom causes N over-application (<5% of fields), but combined manure and commercial fertilizer use consistently exceeds crop N requirements by 10–55% depending on rate assumptions. The study identifies spatial hotspots—such as central Minnesota—where the risk of localized over-application is particularly acute due to concentrated livestock production. The authors conclude that a more integrated approach to nitrogen management, which fully accounts for manure-N, is essential both for reducing environmental contamination and for realizing substantial fertilizer cost savings.