DRAINMOD simulation of drain spacing impact on canola yield in heavy clay soils in the Canadian prairies

Excess moisture within the root zone due to the shallow water table is a leading cause of crop loss in Manitoba. In this study, the ability of the DRAINMOD model to predict water table depth (WTD) in clayey soil was evaluated using measured field data from the 2019 and 2020 canola-growing seasons in Arborg, Manitoba, Canada. Statistical analysis and graphical plots showed close agreement between the measured and simulated WTD with an overall coefficient of determination (R-2), root mean square error (RMSE), mean average error (MAE) and mean bias error (MBE) of 0.93, 9.84 cm, 7.06 cm and -0.13 cm, respectively. Since the model simulation was deemed satisfactory, the model was run with 30-year historical climate data to assess the impacts of different drain spacing on canola yield. Simulation results showed that the average surface runoff increased while average drainage and relative canola yield decreased as drain spacing increased. The simulation results suggest that long-term average yield would be maximized by close drain spacing <= 15 m. Economic analysis showed that 10 m drain spacing would maximize the return on investment. The need for long-term simulations to develop appropriate site-specific water management strategies is demonstrated.