The implementation of cover crops in Iowa has the potential to decrease soil erosion, weed density, and nitrate leaching while increasing soil organic carbon. This study investigated nine potential cover crops; winter rye (Secale cereale L.), winter triticale (Triticale hexaploide Lart.), two winter canola (Brassica napus L.) varieties, winter camelina [Camelina sativa (L.) Crantz], spring barley (Hordeum vulgare L.), spring oat (Avena sativa L.), purple top turnip (Brassica rapa L.), and hairy vetch (Vicia villosa Roth). Cover crops were planted as sole crops and selected binary and trinary mixtures. A control treatment of no cover crop was included. Cover crops were no-till drilled immediately after soybean harvest. The study included five site years with 2013-2014 at Ames, and Lewis, IA and 2014-2015 at Boone, Lewis, and Sutherland, IA.

Results across all site years showed that rye and rye mixtures produced the most spring aboveground biomass, C, and N accumulation, had the highest C/N ratios, resulted in some of the lowest soil nitrate concentrations, and generally produced the lowest SPAD corn leaf chlorophyll readings. Rye accounted for more than 79% of the spring aboveground biomass accumulation in rye mixtures. Triticale and camelina monoculture produced approximately 50% less biomass than cover crops which included rye. Cover crops did not influence soil temperature, soil P or K concentrations, weed density, weed community, or corn yield. Cover crops had a limited influence on volumetric soil water content. Cover crop mixtures had no advantages over cover crop monocultures except for increasing fall stand density. Turnip and vetch had limited winter survival. Spring barley, spring oat, and both varieties of canola winterkilled.