Observed and simulated water table depths in subsurface drained soils in northwest Minnesota

Farmers are increasingly considering the use of subsurface drainage in northwest Minnesota where annual precipitation averages 560 to 640 mm. Results of field observations and DRAINMOD simulation of water table depths in two soils of the Red River of the North Basin in Northwest Minnesota are presented. Water table reductions primarily occurred between April and June when crop ET is small and snowmelt and rainfall increase soil moisture. The effectiveness of drainage depended on drain spacing and soil properties. Narrow drain spacings were more effective at lowering seasonally high water tables than wider spacings. The DRAINMOD simulation showed that a simple calibration of the model by adjusting the monthly ET factors was sufficient to allow the model to simulate the high water tables associated with large summer rainfall events, but simulated water tables receded faster than those observed in the field. The model performed more poorly in the early spring when snowmelt and soil thaw processes occurred. Research continues to improve the simulation of drainage on these soils.