Simulation of N 2O emissions from an irrigated dairy pasture treated with urea and urine in Southeastern Australia

Abstract

The irrigated dairy pasture system in Australia is a high input–high output production system associated with intensive irrigation and nitrogen (N) fertilizer applications. The environmental impacts of such systems are attracting increasing attention in terms of greenhouse gas emissions, such as carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O). In this study, the daily and total chamber-measured N 2O emissions from an intensively-irrigated pasture grown on a clay loam-textured soil for non-fertilized (CK), urea and urine treated plots at Kyabram in Southeastern Australia were measured over a period of 20 months and compared with the predictions by a process-based agroecosystems model, water and nitrogen management model (WNMM). WNMM was capable of estimating daily and annual N 2O emissions but with different levels of success during different seasons and at different temporal scales. The simulations and statistical analysis indicated that the performance of WNMM in predicting the daily and monthly N 2O emissions for the three treatments is in the order: CK < urea < urine. The periodically-summed correlation analysis showed that WNMM was most reliable in predicting N 2O emissions from an intensively-irrigated dairy pasture system at a time scale of around 35 days. The WNMM-estimated N 2O emission factor for this ecosystem was around 0.5%. WNMM has the potential to test agricultural practices, in this case irrigation and fertilizer N application, for mitigating direct N 2O emissions for an irrigated pasture system.