Daycent Simulations of Long Term Irrigated Corn Rotations in Colorado.

The DayCent biogeochemical model was tested using N2O, crop yield, soil N and C, and other data collected from irrigated cropping systems in northeastern Colorado during 2002-2014. DAYCENT uses daily weather, soil texture, and land management information to simulate C and N fluxes between the atmosphere, soil, and vegetation. The model properly represented the impacts of tillage intensity and N fertilizer amount on crop yields, soil organic C (SOC), and soil water content. DAYCENT N2O emissions matched the measured data in that simulated emissions increased as N fertilization rates increased and emissions from no-till (NT) tended to be lower on average than conventional-till (CT). However, the model under-estimated N2O emissions and crop yields for the plots that were not fertilized with N. Both the model and measurements showed that soil NO3- levels increase with N fertilizer addition and with tillage intensity, but DAYCENT underestimated NO3- levels, particularly for the treatments receiving no N fertilizer.  Results suggest that improved representation of plant N uptake will also lead to better model estimates for soil mineral N levels and N2O emissions.