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Nitrous Oxide Emission from a Spray Field Fertilized with Liquid Lagoonal Swine Effluent in the Southeastern United States
Stephen C. Whalen1, Rebecca L. Phillips2, and Eric N. Fischer3
Contemporary agriculture is characterized by the intensive production of livestock 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 associated with industrial scale, swine-production facilities that have rapidly expanded in the southeastern United States. In an intensive, 24-day investigation over three spray cycles, we followed the time course for changes in N2O emission and soil physicochemical variables in an agricultural field irrigated with liquid lagoonal swine effluent. The total-N [535 milligrams per liter (mg/L-1)] of the liquid waste was almost entirely NH4+-N (>90%) and thus had a low mineralization potential. Soil profiles for nitrification and denitrification indicated that >90% of potential activity was localized in the surface 20 centimeters (cm). Application of this liquid fertilizer to warm (19 to 28oC) soils in a form that is both readily volatilized and immediately utilizeable by the endogenous N-cycling microbial community resulted in a sharp decline in soil NH4+-N and supported a rapid and short-lived (days) burst of nitrification, dentrification, and N2O emission. Fluxes of nitrous oxide as nitrogen (N2O-N) as high as 9,200 micrograms per gram dry weight of soil per hour (m g gdw-1 h-1) were observed shortly after fertilization, but emissions decreased to prefertilization levels within a few days. Poor correlations between N2O efflux and soil physicochemical variables (temperature, moisture, NO3--N, NH4+-N) and fertilizer-loading rate point to the complexity of interacting factors affecting N2O production and emission. Total fertilizer N applied and N2O-N emitted were 29.7 grams per square meter (g/m-2), and 395 milligrams per square meter (mg/m-2), respectively. The fractional loss of applied N to N2O (corrected for background emission) was 1.4%, in agreement with the mean of 1.25% reported for synthetic fertilizers. The direct effects of fertilizer application appear to be more immediate and short-lived for liquid swine waste than for manures and slurries that have a slower release of nitrogenous nutrients.
1University of North Carolina, Department of Environmental Science and Engineering, Chapel Hill, NC 27599-7400 (firstname.lastname@example.org)
2University of North Carolina, Department of Environmental Science and Engineering, Chapel Hill, NC 27599-7400 (email@example.com)
3University of North Carolina, Department of Environmental Science and Engineering, Chapel Hill, NC 27599-7400 (firstname.lastname@example.org)
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