Date Full Report Received03/20/2008
Date Abstract Report Received03/20/2008
InvestigationInstitution: University of Nebraska
Primary Investigator: Charles Wortmann
Co-Investigators: Charles Shapiro, Aaron Nygren
Funded ByNebraska Pork Producers Association
Swine slurry contains nitrogen primarily in organic and ammonium forms. Ammonium-N is immediately crop available following land application if not lost to volatilization which should be minimal if the slurry is injected. Crop availability of N from the organic fraction is less predictable. The effects of application time, soil water, and soil texture on release of organic N were studied by the University of Nebraska-Lincoln with the application of approximately 150 lb/acre of N. Soil water management was important as 85% more ammonium plus organic N from manure became plant available with irrigation than with rainfed conditions. Soil type was also important with 46% more N plant available N with a silt loam compared with a loamy sand soil. With fall and early spring applied manure, 67 lb/A of plant available N was available from swine slurry by early May, primarily as nitrate-N. By the end of July, >87 lb/A had become available for each application time. On average, approximately 114 lb/A or 76% of the manure N became plant available by the time a corn crop would be physiologically mature. Swine slurry N became available, therefore, as the season progressed, but on average, less than predicted became available. Time of application was important to organic N mineralization with 83% of the applied organic N mineralized with fall application while net mineralization of organic N was not detectable by the end of the crop growing season with May application. These rates of organic N release were greater than observed for feedlot manure. In Nebraska, estimates of 100% of the inorganic N and 35% of the organic N in swine slurry become available to the first crop if the slurry is injected. These estimates were confirmed for fall and early spring application if the crop is irrigated. However, the study found less to be available under rainfed condictions, especially for a loamy sand soil and that less is available with late spring application. The results were, however, quite variable across application times and sampling dates, reminding us that there is a margin of error in estimating plant available N from swine slurry. Less will become available than expected with some applications implying potential for under-supply of N to the crop while more will become available with other applications implying increased potential of nitrate-N loss to ground water or drainage water. High efficiency of use for N supplied in swine slurry can be achieved while ensuring adequate N for the crop and preventing excess nitrate-N leaching by planning to supply no more than 80% of the crop N need for slurry. Additional fertilizer N can be applied in-season by sidedressing or fertigation when the need for additional N is determined by use of the pre-sidedress nitrate test or based on leaf chlorophyll content. Nutrient management records will become valuable in understanding N availability from swine slurry for given fields and management conditions so that rates of swine slurry N rates can be gradually fine-tuned.