Field Evaluation of DRAINMOD 5.1 Using Six Years of Data from an Artificially Drained Agricultural Field in North Carolina

The performance of the water table management simulation model DRAINMOD 5.1 was evaluated using 6 years of data from an artificially drained agricultural site located in North Carolina Lower Coastal Plain. The site is nearly flat with very poorly drained sandy loam soil. Four experimental plots planted to a corn-wheat-soybean rotation and managed using conventional and controlled drainage, were used in this testing. Water table depth midway between drains and drainage rates were measured and meteorological data were recorded continuously. Simulation results showed very good agreement between observed and predicted water table depths. On average over the 24 simulated plot-years, predicted water table depth was within 12.4 cm of observed values with an average coefficient of determination (R2) of 0.775. DRAINMOD predictions of subsurface drainage were also in very good agreement with observed values. The absolute normalized errors in predicting annual subsurface drainage were less than 5% in almost half of the 24 simulated plot-years. Cumulative drainage over the whole simulation period was slightly overpredicted by 0.8% for one plot and under-predicted by 5.3, 4.3, and 13.2% for the other 3 plots. Results of this study showed that DRAINMOD 5.1 can reliably predict the hydrology of drained soils.