Investigating the Effects of Grass-Legume Winter Cover Crop Mixtures on soil Nitrogen Supply in Rolling Cropland

Sustainable cereal production systems rely upon healthy topsoils and biologically-based nitrogen sources. Previous research has shown that grass/legume cover crop mixtures can provide soil conservation benefits, while also increasing the plant available nitrogen to a subsequent corn (Zea mays L.) crop. However, our understanding of the multifunctional benefits of cover crop mixtures is based largely on research conducted in uniform, plot-scale settings that are not representative of farmers’ fields. Rolling-hill landscapes make up a large portion of farmland in the southeastern United States and present a challenge for grain crop producers in the region because they possess areas of high soil fertility interspersed with regions of low fertility. We hypothesize that grass/legume cover crop mixtures will reduce this spatial variability. In particular, we hypothesize that legume species will dominate, add more nitrogen, and release nitrogen more quickly in lower-fertility sloping positions, whereas grass species will dominate, scavenge nitrogen, and release it more slowly in higher-fertility summit and depressional positions. We propose to test these hypotheses using a field experiment at two on-farm locations and two research farm locations. We plan to measure the biomass, species composition, nitrogen fixation, and nitrogen release of grass/legume cover crop mixtures at different landscape positions. Knowledge about cover crop effects on soil nitrogen supply gained from this research will be shared with farmers through on-farm data collection and at field days.