Are distinct nitrous oxide emission factors required for cattle urine and dung deposited on pasture in western Canada?

While some countries disaggregate N2O emission factors for urine and dung deposited onto pastures, in Canada, distinct N2O emission factors for beef cattle urine and dung have not been defined. To help address this knowledge gap, we conducted a 1-year study to quantify N2O fluxes from beef cattle urine and dung patches on a semiarid tame pasture in western Canada, as well as to quantify the N2O emission factors (EF3) for urine and dung as the percentage of applied N emitted as N2O-N. Urine and dung were deposited when soil water-filled pore space was nearly 60%, a wet soil condition for the grazing season in the semiarid study region, which led to a burst of N2O from urine in the first 14 days of the study (42% of total N emitted). Urine emitted more cumulative N2O (P < 0.001) and had a greater N2O emission factor (P = 0.002) than dung. The urine patch emitted 1.30 ± 0.47 g N2O-N m-2 year-1, while the dung patch emitted 0.083 ± 0.020 g N2O-N m-2 year-1 (mean values ± SD). The N2O emission factor for urine was 1.32 ± 0.49%, while for dung it was 0.03 ± 0.02%. We conclude that more study is needed to determine if distinct N2O emission factors are required for urine and dung deposited onto pasture in western Canada to more accurately estimate national N2O inventories.