Interactions between Landscape Topography and Cover Crops in a Southeastern Corn Cropping System.

Crop production systems in the southeastern United states are commonly dominated by rolling hill style topography. Landscape complexity in these systems can lead to challenges for producers, as downslope movement of soil water and soil nutrients can give rise to the development of spatial zones of varying productivity. The integration of a winter cover crop may mitigate some of this variability by increasing soil water and nutrient retention and decreasing the erosion of topsoil, moderating some of the processes that lead to instability in productivity across these rolling hill systems. We evaluated the ability of a cereal rye (Secale cereale L.) monoculture and a cereal rye/crimson clover (Trifolium incarnatum L.) mixture to mitigate spatial variability in corn yield across areas of varying landscape topography at two locations. In addition, we examined the effect of landscape position on the decomposition rates of cover crop residue, aboveground biomass production, and the amount of nitrogen derived from atmospheric fixation by the leguminous clover species. We found a significant effect of landscape position on cover crop biomass productivity, with toeslope areas producing increased biomass at one site, but environmental conditions leading to different results at the other. The species composition shifted across landscape positions at both field sites, with the proportion of clover within the total biomass of the mixture treatment positively correlated with the slope. Nitrogen fixation rates of the legume were also significantly influenced by landscape position, with clover grown in backslope areas deriving significantly more nitrogen from atmospheric fixation relative to clover grown in toeslope and summit areas. Landscape position was shown to be a major driver of differences in corn yields across the landscape. We did not observe a significant effect of cover crop on maize yield across any landscape position, under both high and no nitrogen fertilizer conditions.