Nitrous oxide emission from an agricultural field fertilized with liquid lagoonal swine effluent

sContemporary agriculture is characterized by the intensive production of l ivestock in confined facilities and land application of stored waste as an organic fertilizer. Emission of nitrous oxide (N2O) from receiving soils is an important but poorly constrained term in the atmospheric N2O budget. In particular, there are few data for N2O emissions from spray fields associa ted with industrial scale swine production facilities that have rapidly exp anded in the southeastern United States. Tn an intensive, 24-day investigat ion over three spray cycles, we followed the time course for changes in N2O emission and soil physicochemical variables in an agricultural field irrig ated with liquid lagoonal swine effluent. The total N (535 mg L-1) of the l iquid waste was almost entirely NH4+-N (> 90%) and thus had a low mineraliz ation potential. Soil profiles for nitrification and denitrification indica ted that > 90% of potential activity was localized in the surface 20 cm. Ap plication of this liquid fertilizer to warm (19 degrees to 28 degrees C) so ils in a form that is both readily volatilized and immediately utilizable b y the endogenous N-cycling microbial community resulted in a sharp decline in soil NH4+-N and supported a rapid but short-lived (i.e., days) burst of nitrification, denitrification, and N2O emission. Nitrous oxide fluxes as h igh as 9200 mu g N2O-N m(-2) h(-1) were observed shortly after fertilizatio n, but emissions decreased to prefertilization levels within a few days. Po or correlations between N2O efflux and soil physicochemical variables (temp erature, moisture, NO3--N, NH4+-N) and fertilizer loading rate point to the complexity of interacting factors affecting N2O production and emission. T otal fertilizer N applied and N2O-N emitted were 29.7 g m(-2) (297 kg N ha( -1)) and 395 mg m(-2), respectively. The fractional loss of applied N to N2 O (corrected for background emission) was 1.4%, in agreement with the mean of 1.25% reported for mineral fertilizers. The direct effects of fertilizer application appear to be more immediate and short-lived for liquid swine w aste than for manures and slurries, which have a slower release of nitrogen ous nutrients.