Estimation of manure nutrient capacity in Nebraska minimizes water quality impacts

Most farmers in the U.S. use inorganic fertilizers. However, using manure fertilizer instead of inorganic fertilizer can better enhance the soil organic matter content while improving soil structure, water-holding capacity and nutrient availability to crops. Additionally, livestock manure can serve as an extra source of income for feedlot operators who redistribute it to area crop farmers as nitrogen fertilizer.

Currently, manure management practices are driven by cropland conditions and proximity to animal feeding operations. But there may be opportunities to improve manure management practices to better distribute nutrients, offering a win-win scenario. Growers would be able to use the manure fertilizer on their crops instead of purchasing and importing inorganic fertilizer and there is less opportunity for over-application and thus, contamination of ground and surface water.

To map out the most optimal distribution of the manure fertilizer, DWFI supported student María José Oviedo Ventura and her DWFI Faculty Fellow advisor Amy Millmier Schmidt, an associate professor of animal science at the University of Nebraska–Lincoln (UNL) and bioenvironmental engineer, first analyzed the feasibility of manure distribution among five Nebraska counties and if there was sufficient manure production to meet crop requirements. She then identified if marketing and transportation from manure surplus production areas could help achieve sustainable nutrient balance.

Results showed that Antelope and Nemaha counties have the highest percentage of highly suitable land for nitrogen-based manure application.

Oviedo-Ventura and Schmidt also found that it is crucial to understand the nature of each county or area and the main drivers for nutrient use locally. As the results suggest, manure can be an excellent nutrient input for crop production. However, the risk of nutrient over-application, and subsequent contamination of ground and surface water sources can exist if it is not carefully managed. It is essential to maintain or create synergies and promote understanding of the benefits of manure application to cropland to encourage its efficient use beyond the boundaries of livestock farms.

Ongoing mapping and modeling efforts, such as the one conducted here, will provide insight into nutrient imbalance risks and opportunities for better distribution of manure nutrients, said Oviedo-Ventura. However, any current and future modeling must be paired with consistent and broad efforts to ensure manure is utilized as a nutrient source on land not owned by livestock producers and that nutrients in manure are properly accounted for when creating crop fertility plans.

Oviedo-Ventura and Schmidt’s research can inform and motivate stakeholders to consider an integrated nutrient management approach at a regional and local scale to address imbalances of nitrogen and minimize negative impacts on water quality in Nebraska.

Oviedo-Ventura successfully defended her master's thesis in July 2023 and received her Masters of Science from UNL in biological systems engineering, mechanized systems management with a focus on water resources. She was born in El Salvador and also holds a Bachelor of Science degree in environmental science and development from Zamorano University in Honduras. Oviedo-Ventura will soon be starting her optional practical training as a bilingual extension support ag educator with the Cornell Small Farms Project.