Effects of bovine urine, plants and temperature on N2O and CO2 emissions from a sub-tropical soil

Grazing ruminants urinate and deposit N onto pastoral soils at rates up to 1,000 kg ha−1, with most of this deposited N present as urea. In urine patches, nitrous oxide (N2O) emissions can increase markedly. Soil derived CO2 fluxes can also increase due to priming effects.While N2O fluxes are affected by temperature, no studies have examined the interaction of pasture plants, urine and temperature on N2O fluxes and the associated CO2 fluxes. We postulated the response of N2O emissions to bovine urine application would be affected by plants and temperature. Dairy cattle urine was collected, labelled with 15N, and applied at 590 kg N ha−1 to a sub-tropical soil,with and without pasture plants at 11°, 19°, and 23°C. Over the experimental period (28 days), 0.2% (11°C with plants) to 2.2% (23°C with plants) of the applied N was emitted as N2O. At 11°C, plants had no effect on cumulative N2O-N fluxes, whereas at 23°C, the presence of plants significantly increased the flux, suggesting plant-derived C supply affected the N2O producing microbes. In contrast, a significant urine application effect on the cumulative CO2 flux was not affected by varying temperature from 11–23°C or by growing plants in the soil. This study has shown that plants and their responses to temperature affect N2O emissions from ruminant urine deposition. The results have significant implications for forecasting and understanding the effect of elevated soil temperatures on N2O emissions and CO2 fluxes from grazed pasture systems.