Cover Crop Options and Mixes for the Upper Midwest.

The implementation of cover crops in Iowa has the potential to decrease soil erosion, weed populations, and loss of nutrients.  Only 1.6% of Iowa farmland is planted to cover crops, most of which is winter rye (Secale cereal L.).  The study investigated nine potential cover crops; winter rye, winter triticale, two winter canola varieties, winter camelina, spring barley, spring oat, purple top turnip, and hairy vetch.  The cover crops were planted as sole crops and selected binary and trinary mixtures.  A control treatment of no cover crop was included. The cover crops were no-till drilled immediately after soybean harvest.  The effects on soil moisture, available soil N, P, and K, weed populations, aboveground cover crop biomass, and corn health and yield were measured.  The study included five sites years with 2013-2014 at Ames, and Atlantic, IA and 2014-2015 at Boone, Atlantic, and Sutherland, IA. Results across all site years show that rye and rye mix treatments accumulated significantly greater quantities of spring biomass (727-809 kg ha^-1), aboveground carbon (299-339 kg ha^-1), and aboveground nitrogen (19.6-21.8 kg ha^-1) than all other cover crop treatments.  Rye and rye mixes were not significantly different from each other in respect to spring biomass, carbon, or nitrogen accumulation.  Soil tests showed that soil NO3-N was greater for the no-cover crop control and treatments with limited or no spring growth.  Cover crop treatment had no effect on soil P or K, weed populations, weed community, or corn yield.  Purple top turnip failed to survive the winter in 4 out of 5 site years.  Spring barley, spring oat, and both varieties of canola never survived the winter.