, Volume 78, Issue 1, pp 51-63
Date: 30 Jan 2007

Application of the DNDC model to tile-drained Illinois agroecosystems: model calibration, validation, and uncertainty analysis

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We applied the Denitrification-Decomposition (DNDC) model to a typical corn–soybean rotation on silty clay loams with tile-drainage in east-central Illinois (IL). Model outcomes are compared to 10 years of observed drainage and nitrate leaching data aggregated across the Embarras River watershed. We found that accurate simulation of NO3–N leaching and drainage dynamics required significant changes to key soil physical and chemical parameters relative to their default values. Overall, our calibration of DNDC resulted in a good statistical fit between model output and IL data for crop yield, NO3–N leaching, and drainage. Our modifications to DNDC reduced the RMSE from 9.4 to a range of 1.3–2.9 for NO3–N leaching and from 51.2 to a range of 13–23.6 for drainage. Modeling efficiency ranged from 0.25 to 0.85 in comparison with measured drainage and leachate values and from 0.65 to 1 in comparison with crop yield data. However, analysis of simulation results at a monthly time step indicated that DNDC consistently underpredicted peak drainage events. Underprediction ranged from 50 to 100 mm month−1 following three extreme precipitation events, a flux equivalent to 0.25–0.5 of the total measured monthly flux. Our simulations demonstrated high interannual variation in nitrate leaching with average annual NO3–N loss of 24 kg N ha−1, peak annual NO3–N loss of 58 kg N ha−1 and low annual NO3–N loss of 1–5 kg N ha−1.