Stephen Del Grosso, USDA ARS NPA SPNR, 2150 Centre Avenue, Building D, Suite 100, Fort Collins, CO 80526 and A.D. Halvorson, USDA-ARS, 2150 Centre Avenue, Building. D, Suite 100, Ft. Collins, CO 80526.
Agricultural soils are the major source of N2O emissions in the USA. Irrigated cropping, particularly in the western USA, is an important source of N2O emissions. However, the impacts of different crop rotations, tillage intensity, and N fertilizer amount and type have not been extensively studied for irrigated systems. The DAYCENT biogeochemical model was tested using crop yield and N2O data collected from irrigated cropping systems in northeastern Colorado during 2002-2006. DAYCENT uses daily weather, soil texture, and land management information to simulate C and N fluxes between the atmosphere, soil, and vegetation. The model did a good job of simulating the impacts of tillage intensity and fertilizer amount on crop yields and soil water content. DAYCENT N2O emissions matched the measured data in that simulated emissions increased as N fertilization rates increased and there was no consistent effect of tillage practice on emissions. However, the model tended to over-estimate N2O emissions, particularly for the no N fertilizer treatments. The model also did not reliably simulate lower emissions following application of polycoated urea compared to liquid urea-ammonium nitrate and dry urea. The model could be improved by accounting for types of fertilizer and how they are applied (e.g., dry surface broadcast vs. liquid band) and modeling time released N fertilizers.