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

Abstract

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.