Simulation of Soil Nitrogen Fluxes and N2O Emissions From An Irrigated Dairy Pasture Applied with Urea and Urine in Southeastern Australia.

The dairy pasture system is a high input and high output agricultural production system, and is associated with intensive irrigation and nitrogen (N) fertilizer applications. The environmental impact of such a system is attracting more concerns in terms of greenhouse gas emissions, such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), and nitrate leaching. In this study, the daily and total chamber-measured N₂O emissions from an intensively-irrigated pastoral clay loam-textured soil for the non-fertilizer (CK), urea and urine treatments at Kyabram in southeastern Australia from 1 Nov 2003 to 30 Jun 2005 (one year and eight months) were compared with the predictions by a process-based agroecosystems model, Water and Nitrogen Management Model (WNMM). The results suggested that WNMM was capable to estimate N₂O emissions, but with different levels of success in different seasons and at different temporal scales, based on the linear regression analysis and two types of correlation analysis (30-day sliding window correlation and summed correlation) when compared with the continuous chamber measurements.

 The agreement between the measured and simulated soil moister, temperature, mineral nitrogen (both nitrate and ammonium) were very good. The WNMM captured the trend of daily N₂O fluxes, but most reliable at the time scale of around 35 days accumulative  emissions. The WNMM-estimated N₂O emission factor for this ecosystem was around 0.5%. The proportions of nitrification-induced N₂O emissions in the simulated annual emissions were 12%, 21% and 45% for the CK, UREA and URINE treatments, respectively.