N Losses from an Andisol via Gaseous N2O and N2 Emissions Increase with Increasing Ruminant Urinary–N Deposition Rate

Agricultural soils account for about 60% of the global atmospheric emissions of the potent greenhouse gas nitrous oxide (N2O). One of the main processes producing N2O is denitrification, which occurs under oxygen-limiting conditions when carbon is readily available. On grazed pastures, urine patches create ideal conditions for denitrification, especially in soils with high organic matter content, like Andisols. This lab study looks at the effects of Urine-urea-N load on the Andisol potential to emit N2O. For this, we investigated the effects of three levels of urea-N concentrations in cow urine on emissions of N2O, N2, and CO2 under controlled conditions optimised for denitrification to occur. Results show total N2O emissions increased with increasing urine-N concentration and indicate that denitrification was the main N2O-producing process during the first 2–3 days after urine application, though it was most likely soil native N rather than urine-N being utilised at this stage. An increase in soil nitrate indicates that a second peak of N2O emissions was most likely due to the nitrification of ammonium hydrolysed from the added urine, showing that nitrification and denitrification have the potential to play a big part in N losses and greenhouse gas production from these soils.