Using RZWQM to Simulate N2O Emissions in an Irrigated Corn Field with Different N Application Rates.

Nitrous oxide (N₂O) emission from agricultural soils is a major contributor to greenhouse gases and climate warming.  Understanding the effects of the interactions between agricultural practices and environmental factors on N₂O emissions will help devise mitigation strategies. In this study, we aimed to evaluate a process-based model, RZWQM (Root zone water quality model), for simulating the response of N₂O emissions to different nitrogen (N) application rates (0, 67, 134, and 246 kg N/ha) on an irrigated corn field in Colorado, from 2003 to 2006. The model has a new algorithm of estimating N₂O emissions from nitrification and denitrification based on previous studies. The RZWQM was first calibrated to adequately simulate corn yield, grain N uptake, soil water (0-180 cm) and soil Nitrate-N content (0-180 cm), with root mean square error values of 1140 kg/ha, 24 kg/ha, 2.0 cm and 58 kg N/ha, respectively, from 2003 to 2006. The calibrated model generally simulated the response of N₂O emissions to N rates fairly well, but over-predicted N₂O emissions especially for the 0 (17%) or 67 kg N/ha (64%) treatments and under-predicted N₂O emission peaks following N applications. The measured and simulated crop yield increased quadratically whereas the annual N₂O emissions increased exponentially with the increased N application rates, which suggests that there is a potential of reducing N₂O emission without decreasing crop yield significantly by reducing N application rate.