Topographical Effects on Performance of Cover Crop Mixtures in Corn and Wheat.

The use of cover crop mixtures in row crop systems could potentially deliver greater ecosystem services than a single species - a legume will fix nitrogen, a grassy species will scavenge nitrogen, some cover crop species enhance weed control, and others contribute more carbon. However, the benefits from cover crop mixtures to soil sustainability and cash crop performance may vary depending on terrain. Plant species have preferred niches; mixtures may overcome field variability by containing plant species that establish in their preferred topographic location. Yet, despite farmers’ interest and high ecosystem service potential, there is only very limited research reported on cover crop mixtures, and no information on their performance in topographically diverse agricultural landscapes of the Midwest. The objective of this study was to assess performance of two cover crop mixtures, cold-hardy and cold intolerant, in corn and wheat, at three contrasting topographical positions. The cold-hardy mixture consisted of annual ryegrass, crimson clover, and dwarf essex rape; the cold-intolerant mixture consisted of oats, winter pea, and radish. Three contrasting topographical positions were (i) summit, (ii) slope (iii) depression. Field experiments were conducted at two experimental sites and 4-5 large fields in Southeastern and Central Michigan in 2016 and 2017. Preliminary results indicate that, while overall cover crop above and belowground biomass was the greatest in topographical depressions followed by summits and slopes, not all species were sensitive to topographical variations, thus affecting the relative composition of the mixtures. Radish and dwarf essex rape performed substantially better in depressions than on slopes and summits, while crimson clover and winter pea were not affected by topography. Greater above-ground biomass produced by oats and radish in the cold-intolerant mixture contributed more to soil organic matter, as indicated by higher particulate organic matter (POM) levels compared with POM in the cold-hardy mixture.