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

Author
item Del Grosso, Stephen - Steve
item Halvorson, Ardell
item PARTON, W - COLORADO STATE UNIV.

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2007
Publication Date: 6/24/2008
Citation: Del Grosso, S.J., Halvorson, A.D., Parton, W.J. 2008. Testing DAYCENT Model Simulations of Corn Yields and Nitrous Oxide Emissions in Irrigated Tillage Systems in Colorado. Journal of Environmental Quality 37:1383-1389.

Interpretive Summary: Agricultural soils are responsible for the majority of nitrous oxide (N2O) emissions in the USA. N2O is a potent greenhouse gas that also impacts ozone chemistry. Irrigated cropping is an important source of N2O emissions. To estimate N2O emissions at regional and larger scales, use of models is required. For example, the DAYCENT ecosystem model is used to estimate N2O emissions from agricultural soils for the US national greenhouse gas inventory. However, DAYCENT has not been extensively tested with field data from irrigated systems. To assess model performance for irrigated systems, DAYCENT was tested using N2O, crop yield, soil nitrogen and soil carbon data collected from irrigated cropping systems in northeastern Colorado. DAYCENT uses daily weather, soil texture, and land management information to calculate carbon and nitrogen exchanges between the atmosphere, soil, and vegetation. Both the model and the field data showed substantial increases in soil carbon and slightly lower grain yields for the no-till compared to the conventional-till system. DAYCENT N2O emissions matched the measured data in that simulated emissions increased as nitrogen fertilization rates increased and emissions from no-till tended to be lower on average than conventional-till. However, the model over-estimated N2O emissions, particularly for the treatments that received no nitrogen fertilizer. Both the model and measurements showed that soil nitrate increases with nitrogen fertilizer addition and with tillage intensity, but DAYCENT underestimated nitrate levels. These comparisons with field data suggest that DAYCENT could be improved by reducing the background N2O emission rate and by accounting for the impact of changes in microbial community structure on N2O emissions.

Technical Abstract: 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 2002-2006. 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 over-estimated N2O emissions, particularly for the treatments that received no N fertilizer. Both the model and measurements showed that soil NO3 levels increase with N fertilizer addition and with tillage intensity, but DAYCENT underestimated NO3 levels. These comparisons suggest that DAYCENT could be improved by reducing the background nitrification rate, by allowing the portion of nitrified N emitted as N2O to vary, and by accounting for the impact of changes in microbial community structure on denitrification rates. [GRACEnet Publication].