Subsurface drainage for promoting soil strength for field operations in southern Manitoba

Successful field operations depend on the ability of the soil to provide traction and support for agricultural traffic and be workable in a desirable manner. This minimizes the risk of soil structural damage to ensure soil conservation and long-term crop yield. In the present study, the objective was to evaluate the performance of subsurface drainage in promoting soil strength for field operations in southern Manitoba. Data obtained from a field study and modeling exercise were used to achieve the objective. The field data include soil water content and watertable depth, which were measured in a potato field during the 2011 growing season. Soil samples were also collected from the field to determine the lower plastic limit (LPL) of the soil. Seventeen-year weather data were used to estimate the reference crop evapotranspiration. The soil strength of drained and undrained sandy-loam fields was compared to evaluate subsurface drainage in promoting soil strength for field operations. The subsurface tile drain was installed at 0.9-m depth and at 15-m spacing. A validated HYDRUS (2D/3D) model was used to extend the study by simulating soil water content dynamics due to different drain spacings (8 m, 10 m, 12 m, 15 m, 20 m, and 30 m) for different years and weather conditions. The soil strength to allow field operations was assessed based on soil water content corresponding to 90% of the LPL in the top 0.3-m depth of the soil, and soil water content corresponding to the LPL in the soil layer between 0.3-m to 0.5-m depth of the soil profile. The soil strength was sufficient to allow field operations when the two criteria were met. In the top 0.3-m depth, the soil strength was sufficient to allow field operations for all the years with or without drainage. Drainage impact was found to be more significant within the 0.3-m to 0.5-m depth of the soil profile throughout the years. Drain spacing less or equal to 12 m promoted soil strength to allow field operations without any significant impact on the number of field workable days during the growing season.