Nitrous oxide emissions from animal urine application on a New Zealand pasture

Animal excreta-nitrogen (N) deposited onto pastoral soils during grazing has been identified as an important source of nitrous oxide (N2O). Understanding the extent and seasonal variation of N2O emissions from animal urine is important for the development of best management practices for reducing N2O losses. The aim of this study was to determine N2O emissions from cow urine after application onto a pastoral soil in different seasons between 2003 and 2005. A closed soil chamber technique was used to measure the N2O emissions from a poorly drained silt loam soil which received either 0 (control) or 1,000 kg N ha−1 (as real cow urine) per application. Application of cow urine to soil increased N2O fluxes above those from the control site for up to 6 weeks, but the duration for which N2O levels were elevated depended on the season. Nitrous oxide emissions were higher during the winter and spring measurement periods when the soil water-filled pore space (WFPS) was mostly above field capacity, and the emissions were lower during the summer and autumn measurement periods when the soil WFPS was below field capacity. The N2O emission factor for urine ranged from 0.02 to 1.52% of N applied. This seasonal effect suggests that a reduction in urine return to soil (e.g., through use of standoff pads or animal housing) under wet conditions in New Zealand can potentially reduce N2O emissions from pastoral soils.