Soil temperature regulates nitrogen loss from lysimeters following fall and winter manure application

Many producers practice fall and winter manure spreading for economic and practical reasons. In order to minimize the risk of nitrogen (N) loss between application and crop uptake in the spring, university extension publications and industry professionals often make recommendations based on soil temperature. The objective of this research, therefore, was to determine how soil temperature affects N losses in runoff and leachate, and assess overwinter N losses based on application date and soil temperature. Phosphorus losses are discussed in a separate article. Dairy manure was surface- applied to a channery silt loam soil contained in lysimeters at soil temperatures of 15.7°C, 4.8°C, and -1.1°C, which corresponded to early fall (Oct. 22), late fall (Nov. 17), and winter (Dec. 15) applications, respectively. Nitrogen losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. The soil temperature between manure application and the first rainfall-runoff event three days after application was held constant and significantly influenced N loss. As the soil temperature decreased, losses of NH₄-N, organic N, and total N exponentially increased. The form of N losses was also significantly impacted by application date and overwinter soil temperature. Early fall application of manure resulted in significant overwinter NO₃-N losses, while the winterapplied manure had significantly more overwinter NH₄-N losses. Results of this research show that there are trade-off risks associated with manure application in the fall and winter and that these trade-offs need to be considered in manure management planning in order to enhance N retention and help reduce the risk of overwinter N losses.