Modeling Water Table Depth, Drain Outflow, and Nitrogen Losses in a Cold Climate Using DRAINMOD 5.1

The performance of the DRAINMOD 5.1 model was tested for conditions, including freezing and thawing, that prevailed at a 4.2 ha field research facility located at St. Emmanuel, Quebec, Canada. Using two years (1998 and 1999) of data collected from the site, the model's ability to predict water table depth (WTD), drain outflow, and nitrate (NO3--N) loads in drain water was tested. The site was arranged in a split-plot design, with two N fertilizer rates (120 and 200 kg ha-1, main plots) factorially combined with two modes of water table management: sub-irrigation (SI) at a WTD of 0.6 m vs. free drainage (FD) at a drain depth of 1.0 m (subplots). The model was calibrated using water table depth and subsurface flow data from 1998 and validated with 1999 data. The model's accuracy was evaluated using the coefficient of determination (R2), modeling efficiency (E), and other statistical parameters. DRAINMOD 5.1 performed well at simulating the number and timing of drainage events in both snowmelt and later-season periods. The model underestimated annual drain outflow under free drainage and sub-irrigation by 12 mm and 20 mm, respectively, in both years. The model simulated the pattern of water table fluctuations fairly well, with R2 values ranging from 0.81 to 0.91, indicating good model fit. The model performed well in predicting total NO3--N loads in subsurface flow, even though there was a tendency to underestimate loads under both free drainage and sub-irrigation treatments.