Topographic effects on soil microclimate and surface cover crop residue decomposition in rolling cropland

Abstract

Rolling hill topography is common in agricultural land throughout the Southeastern United States. In areas of complex topography, downslope movement of soil nutrients and water can lead to nutrient losses and soil degradation, as well as spatial yield variability. Additionally, differences in the accumulation of water, slope aspect, and crop biomass production can lead to disparate conditions of soil moisture and soil temperature throughout a given field. Winter cover crops can reduce erosion and mitigate nutrient losses, while also potentially providing a source of nitrogen (N) to the subsequent cash crop as the cover crop residue decomposes. However, given that moisture and temperature at the soil surface are primary controls on residue decomposition, topographic heterogeneity may lead to variable rates of cover crop breakdown and N return to the system. We investigated the effect of landscape position on soil volumetric moisture and temperature at 5 cm depth, and the decomposition and N release rate of two cover crop residues, a sole-seeded cereal rye (Secale cereale L.) cover crop, and a cereal rye/crimson clover (Trifolium incarnatum) mixture over two maize (Zea mays L.) growing seasons in Lexington, KY. We found differences in soil moisture and soil temperature across landscape positions, with backslope positions tending to be the warmest and driest positions, and toeslope positions tending to be wettest. However, we did not observe significant differences in decomposition or residue N release rate among landscape positions or cover crop treatments. Our results emphasize the inherent variability present in abiotic factors in rolling hill cropland but indicate that cover crop residue persistence and N release are relatively consistent among landscape positions.