Deep-rooted cover crops may help alleviate effects of soil compaction, especially in no-till systems. We evaluated the compaction-alleviating ability of 4 cover crops (rape, oilseed radish, forage radish and cereal rye). The experiments were conducted at the University of Maryland Wye Research Station and Education Centre on a Mattapex silt loam (Aquic Hapludults) and at the USDA Beltsville Agricultural Research Centre on an Elkton silt loam (Typic Endoaquults). Using a minirhizotron camera, we observed soyabean ( Glycine max) roots growing through compacted plough pan soil using channels made by decomposing cover crop roots. Soyabean yield response to the preceding cover crops was most pronounced at the site with most severe drought and soil compaction. At this location, with or without deep tillage, soyabean yields were significantly greater following a forage radish cv. Diachon+rye combination cover crop. Rye left a thick mulch, resulting in conservation of soil water early in the season. Root channels left by forage radish may have provided soyabean roots with low resistance paths to subsoil water. Due to lower than normal winter precipitation, this study was a conservative test of the cover crops' ability to alleviate the effects of soil compaction.
