Assessment of Integrated Nutrient Management Practices on Soil Health and Nitrogen Efficiency in Cropping Systems

Groundwater quality in Nebraska is threatened by non-point source contributions of nitrate-nitrogen, primarily by agricultural systems. Intensive crop and livestock production that neglects the value of manure in crop fertility plans can contribute to soil degradation and natural resource impairment. The purpose of this study is to evaluate opportunities to improve agricultural nutrient management throughout Nebraska by quantifying opportunities for manure distribution, evaluating soil health implications of organic and inorganic soil amendments, and assessing nutrient management practices focused on reducing nitrate leaching in agricultural soils. This study described in Chapter 2 provides a spatial illustration of nitrogen and phosphorus balances in five Nebraska counties and the capacity for assimilating manure nutrients based upon land suitability statewide for manure application. Results suggest that there is potential for improving manure management practices to better distribute nutrients, mainly driven by cropland assimilative capacity and geographic conditions. Nitrogen use efficiency in cropping systems is largely impacted by nutrient form (inorganic vs. organic), soil properties, and environmental conditions. Chapter 3 describes field research to assess soil physical, chemical, and biological properties on irrigated and dryland sandy loam soil receiving inorganic and organic nutrient and carbon amendments. Results provided evidence that short-term changes in soil biological quality due to nutrient and carbon inputs can be differentiated within a single cropping season. Demonstrating short-term improvements that indicate potential for improving long-term cropland resilience may improve farmer acceptance of organic nutrient and carbon sources. The final study, reported in Chapter 4, was performed to assess the fate of nitrogen in soil based upon nitrogen source and inclusion of a nitrification inhibitor. Surface-applied urea, beef feedlot manure, poultry litter, and swine slurry manure, each with and without nitrapyrin, were evaluated. Nitrogen sources influenced soil nitrogen dynamics more than nitrification inhibitors; nitrification inhibitors were only effective when used with inorganic nitrogen fertilizer (urea). Among manure sources, beef manure demonstrated the lowest risk for nitrogen losses to groundwater. Advisors: Amy M. Schmidt and Javed Iqba