Subsurface Drainage for Minimizing the Risk of Subsoil Compaction in Seasonally-Frozen Soils

Abstract

HighlightsSubsoil is highly susceptible to compaction based on texture and packing density.Imperfect natural drainage increases the risk of subsoil vulnerability to compaction.Irrespective of drain spacing, the risk for subsoil compaction was high.The upper soil layer protects the subsoil from compaction at drain spacing = 12 m in this soil. Abstract. Subsoil compaction negatively impacts soil hydrological processes and promotes anaerobic conditions, reducing soil productivity and enhancing greenhouse gas emissions from the soil. Additionally, it is challenging and expensive to alleviate subsoil compaction once it occurs. The objective of this study was to assess the effectiveness of subsurface drainage in minimizing the risk of subsoil compaction under different weather patterns in Southern Manitoba. The assessment of the risk of subsoil compaction was done in two stages. That is, 1) determination of the subsoil’s intrinsic susceptibility to compaction based on soil texture and packing density and 2) determination of the wetness condition of the subsoil and ability of the strength of the upper layer of the soil to protect the subsoil. A long-term simulation of soil water content data (i.e., 2000 to 2015) under different drainage spacings (i.e., 8, 10, 12, 15, 25, and 30 m) maintained at 0.9-m depth was obtained to determine the soil wetness condition using a validated HYDRUS 2D/3D model. The study showed that the subsoil’s intrinsic susceptibility level to compaction at the study site was high, implying that the subsoil had a very weak natural potential to resist compaction. Throughout the 16 years considered, the subsoil wetness condition was either “moist” or “wet” irrespective of drain spacing, making the subsoil very vulnerable to compaction. However, for drain spacing = 12 m, the subsoil was found to be protected for most of the spring operation period with minimum impact on the spring operation days based on the criterion that the soil water content in the upper layer should be equal to or less than 90% of the lower plastic limit. In contrast, drain spacing wider than 12 m resulted in a lack of protection of the subsoil for 21 to 50 d. The intrinsic susceptibility of the subsoil to compaction, the “imperfect” internal natural drainage, and excess soil water during the early growing season suggest it is critical to consider the benefits of installing subsurface drains at narrower spacing (= 12 m) because of the ability to improve the soil wetness condition for field operations and prevent short and long-term impacts due to subsoil compaction. Keywords: Bulk density, HYDRUS (2D/3D), Lower plastic limit, Sandy loam, Soil water content.