Subsurface drainage effects on soil penetration resistance and water table depth on a clay soil in the Red River of the North Valley, USA

Since 1993, the Red River of the North Valley in North Dakota (ND) and Minnesota (MN), in the USA has experienced increased annual rainfall which has caused localized seasonal soil waterlogging and inhibited crop yield potential in the unique, high water table clay soils of the region. Subsurface (tile) drainage has been increasingly considered by farmers to help reduce excess water in the crop root zone. Producers desire to manage the water table for optimizing yield and trafficability of the field. The objective of this research was to evaluate differences in soil penetration resistance and water table depth between subsurface (drained) and non-subsurface drained treatments (undrained), using water control structures, in fallow, and cropped soybean (Glycine max L. Merr.) and wheat (Triticum aestivum L. emend. Thell.) cultivars on a Fargo-Ryan silty clay soil near Fargo, ND, USA in 2009 and 2010. The experimental design was a randomized complete block in a split-plot arrangement with four replicates. The whole plot treatments were drained and undrained (control structures opened and closed, respectively). Soil penetrometer readings and water table depth were measured weekly. Yields of each crop were not different comparing drained and undrained treatments in 2009 and 2010. The depth averaged drained penetration resistance was 1,211 kPa compared with 1,097 kPa for undrained treatment, averaged across 2009 and 2010. The depth-averaged drained penetration resistance values for fallow, soybean, and wheat were 1,077, 1,137, and 1,420 kPa, respectively. The undrained values for fallow, soybean and wheat were 1,001, 1,021, and 1,267 kPa, respectively, all significantly lower than the drained treatments, indicating that the drained soil is capable of a higher load carrying capacity compared to the undrained soil. The average depth to the water table was greater on drained soil compared to the undrained soil both early and late in the growing season. Forty two percent of the variation in the penetration resistance can be explained by the level of the water table below the surface. Water control structures can be used to manage the water table level and soil penetrations resistance. The ability for land managers to enter drained fields with farm equipment earlier will likely extend the length of the growing season and potentially increase crop yields in this region.