Research Experience With Cover Crops in the Semi-Arid Northern U.S. Great Plains.

Cover crops provide potential for soil improvement as partial fallow replacements or full season growth in integrated crop-livestock systems. Annual legume green manures (LGMs) may improve soil nitrogen cycling but farmer adoption remains very low. In the past decade we have compared legume species, spring vs winter growth habits, plant density, tillage management, and long-term LGM effects on wheat N uptake, mainly within no-till systems. Growth, total biomass N yield, and weed competition of pea was superior to lentil. Winter pea, when it survived, provided superior biomass N to spring pea. Seed cost is a barrier to adoption but we found only minor potential for reducing seeding rates without compromising N fixation and weed competition. Tillage, even once, increased N contribution of LGMs. Overall, short-term effects of LGMs were inconsistent, especially for spring-sown legumes. However results from a 10-yr study of pea-wheat crop rotations near Bozeman, showed superior N cycling by the LGM treatment with time, similar to reports from two other studies in this region at Culbertson, MT, and Swift Current, SK. At Mandan, ND, the use of full season cover crops has shown value in integrated crop-livestock systems, especially with swath grazing. Integrated crop-livestock systems were found to reduce winter feeding costs without adversely affecting near-surface soil quality. There is widespread interest in cover crop mixtures (CCMs) currently in the northern Great Plains. Research was begun near Mandan in 2009 and in Montana in 2012 on this topic. Preliminary results and future research needs will be discussed.