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Testing DAYCENT Model Simulations of Corn Yields and Nitrous Oxide Emissions in Irrigated Tillage Systems in Colorado

^a USDA, Agricultural Research Service, 2150 Centre Ave, Bldg. D, Ste. 100, Fort Collins, CO 80526
^b Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO 80523

^* Corresponding author email (steve.delgrosso{at}ars.usda.gov).

Received for publication June 1, 2007. Agricultural soils are responsible for the majority of nitrous oxide (N₂O) emissions in the USA. Irrigated cropping, particularly in the western USA, is an important source of N₂O emissions. However, the impacts of tillage intensity and N fertilizer amount and type have not been extensively studied for irrigated systems. 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 to 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 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 overestimated N₂O emissions. Lowering the amount of N₂O emitted per unit of N nitrified from 2 to 1% helped improve model fit but the treatments receiving no N fertilizer were still overestimated by more than a factor of 2. 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. We suggest that DAYCENT could be improved by reducing the background nitrification rate and by accounting for the impact of changes in microbial community structure on denitrification rates.

Abbreviations: CT, conventional till • GHG, greenhouse gas • GWP, global warming potential • NT, no-till • SOC, soil organic carbon

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