Cover Crop Effects on Cash Crops in Northern Great Plains No-till Systems Are Annually Variable and Possibly Delayed

Cover crop adoption in conventional no-tillage corn/soybean production systems has been limited due to the lack of specific information regarding the impact of cover crops on cash crop performance. Within a no-till small grain/cover crop-corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation in eastern South Dakota, we evaluated the impact of fall-planted forage oat (Avena sativa L.), hairy vetch (Vicia villosa Roth), winter canola (Brassica napus L.), and a combination of all three compared to a no cover crop treatment on soil nutrient dynamics, biomass, nutrient uptake, and grain yield of the immediatelyfollowing corn crop. At site-year 1, where cover crop growth was most consistent, corn yield was significantly higher with oat, vetch, and a combination of all three cover crops compared to the no cover crop treatment. At site-year 2, corn yields were equivalent among treatments except the combination treatment which was significantly lower. At site-year 3, corn yields in the canola and oat treatments were equivalent to no cover crop, while corn yields with vetch and the combination treatments were lower. Corn biomass and nutrient uptake responded to treatments similarly to corn yields. For site-years 1 and 2, some cover crop treatments resulted in modest, but significant increases in soil N during spring. For site-year 3, the combination treatment immobilized N during the corn vegetative growth phase but released N during the reproductive phase. Cover crop treatments had little effect on plant-available soil P. However, soybean yields two years following cover crop treatments were higher for all three site years with cover crops compared to no cover crop, with this difference significant in two of the three site-years. Immediate effects of cover crops on the following cash crop under no-till were variable and depend on both fall and spring cover crop biomass, which in turn are dependent on the amount and timing of precipitation and temperature patterns. Cover crops in no-till systems may produce more consistent but possibly delayed benefits by boosting yields of cash crops in later years as cover crop residues decompose.