Characterization of ammonia emissions from soils in the upper coastal plain, North Carolina

A dynamic flow-through chamber system was used to measure fluxes of ammonia-nitrogen (NH3-N, where NH3-N=(14/17)NH3) from soil surfaces. The research site was located in eastern North Carolina (35.9°N latitude; 77.7°W longitude) and measurements were conducted during spring and winter 2000, in order to assess the NH3 source strength of intensively managed agricultural soils and the physiochemical properties which control these emissions. Soil temperature (Tsoil), soil pH, soil moisture, total Kjeldahl nitrogen (TKN=organic N+NH3-N+NH4+-N) were monitored throughout both research periods. Soil temperature was found to explain the largest variability in soil NH3 emissions (Log10 NH3-N Flux=0.054Tsoil+0.66; R2=0.71), suggesting that an approach similar in design to the biogenic emissions inventory system land use and temperature model for NO emissions, might be effective for modeling biogenic NH3 emissions. Soil nitrogen was also significant in predicting NH3 flux [NH3 Flux=55.5(NH3-N)−160, R2=0.86; NH3 Flux=0.6(TKN)−410, R2=0.27], but only after the two days with the heaviest rainfall were removed from the regression, emphasizing the role of soil moisture in controlling the transfer of gases across the soil/air interface. Soil pH remained relatively constant throughout both research periods and therefore did not serve as a useful predictor of NH3 flux. A rain event, followed by a drying period produced a characteristic pulse in ammonia emissions. This pulsing phenomenon has been observed for other trace gases by various researchers. This research location was the site of a commercial hog operation, which allowed for the comparison of soil and lagoon emissions (lagoon emissions were based on an algorithm developed by Aneja et al. (J. Geophys. Res. 105 (2000) 11,535). An analysis of the source strengths confirmed that lagoon emissions are a larger flux source (average lagoon flux 18,137 ng N m−2 s−1; average soil flux 54 ng N m−2 s−1); however soil surfaces make up a larger fraction of a commercial hog operation than the lagoon surfaces, and as a result they cannot be neglected when developing and apportioning NH3 emissions. A yearly average of ammonia emissions at this site revealed that soil emissions represent approximately 28% of the lagoon emissions.