Three methods to estimate N2O fluxes as impacted by agricultural management

This study examines three methods of evaluating N2O flux and accumulation in soil profile over a growing season under three soil management regimes (fallow, fallow with manure addition and cropped to alfalfa). Estimates of N2O flux were made based on measured soil atmosphere concentration gradients in the top 15 cm and compared to flux estimates based on ex situ cores and micro-meteorological measurements made in parallel studies. All methods indicated strong seasonal trends relating to precipitation events. The amounts of N2O accumulating the profile decreased in the order alfalfa < fallow < fallow/manure. The amounts of N2O accumulating in the profile ranged from ambient (0.35 mu L L-1) to 490 mu L L-1. Diffusion of N2O to the lower profile was shown to provide temporary storage of N2O and 2 thereby provide the opportunity for further reduction to N-2 prior to efflux from the surface. In comparing the estimates of surface flux, all three methods were of the same order of magnitude for the fallow site but profile-based estimates were much lower and much higher for fallow/manure and alfalfa sites, respectively. Differences were attributed to the location and timing of carbon addition in each system.