Simulating N2O Emissions in Different Tillage Systems of Continuous Corn Using RZWQM2-SHAW Model.

Nitrous oxide (N2O) is one of the most important greenhouse gases of the 21st Century due unchecked emissions and persistence in the atmosphere. Soil fertility management makes agriculture a primary source of global N2O emissions. Yet, emissions can vary by crop type, management, with differences in year due to environmental conditions that govern soil moisture and temperature. Ecosystem models are important tools to estimate N2O emissions from specific crop management practices and by accounting for temporal variability may help improve regional estimates. Recently, RZ2-SHAW was modified to simulate N2O emissions. The objective of this study is to test RZ2-SHAW accuracy in predicting N2O emissions from different tillage management at two fertilizer application rates from an irrigated continuous corn (Zea mays L.) system in Colorado. RZ2-SHAW coupled model was used to account for differences in soil surface temperatures between tillage systems. Crop measurements and soil trace gas samples were collected through the 2003 to 2006 corn growing season at Agricultural Research and Development Education Center (ARDEC) in Colorado. Model calibrations were based on conventionally tilled cropping system and high N rate from the study by Fang et al. (2014). Simulated crop yield was close to the measured data, with a slight over prediction of 0.1 Mg ha-1 in HN-NT and CT systems, with corresponding RMSE values of 0.9 Mg ha-1 (0.7%) and 1.6 Mg ha-1 (0.9%), respectively. Soil temperature was under predicted in HN-NT and CT systems, with MD values of -1.6 and -0.33, respectively. Soil water in the 0-180 cm profile was under simulated by 1.6 cm in N-T system, and better prediction of profile soil water (cm) was made in the HN-CT treatments due to drier conditions. Predicted N2O emissions were under simulated by 0.10 (1.5%) and 0.56 (7.1%) g N2O ha-1 day-1 for HN-NT and CT systems, respectively. RZ2-SHAW model correctly predicted cooler soil temperatures and lower N2O emissions in the NT system. Annual variability of N2O emissions in the NT system was simulated by RZ2- SHAW model, indicating that the model made reasonable prediction of N2O emissions in different tillage systems irrigated under continuous corn.