Investigating the Effects of Grass-legume Winter Cover Crop Mixtures on Soil Nitrogen Supply in Rolling Agricultural Landscapes

View the project final report

Commodities

• Agronomic: clovers, corn, rye

Practices

• Crop Production: cover crops, nutrient management

Sustainable cereal production systems rely on healthy soils and biologically based nitrogen. 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 hypothesized that grass-legume cover crop mixtures would reduce this spatial variability. In particular, we hypothesized that a legume species would produce more biomass, add more nitrogen, and release nitrogen more quickly in lower-fertility sloping positions, whereas grass species would produce more biomass, scavenge nitrogen, and release it more slowly in higher-fertility summit and depressional positions. We tested these hypotheses using a field experiment at two on-farm locations and two research farm locations. We measured the biomass, species composition, nitrogen fixation, and nitrogen release of cereal rye (Secale cereale L.)/crimson clover (Trifolium incarnatum) mixtures as compared to monoculture cereal rye at different landscape positions (summit, backslope, and toeslope). In general, the toeslope position was the most productive in terms of cover crop biomass and nitrogen accumulation. The crimson clover biomass and fixed N increased with increasing slope and sand percentage. The rate of cover crop nitrogen release was similar among landscape positions and between the rye and mixture cover crops. However, there tended to be more nitrogen released by the mixture than the rye monoculture on the backslope position. The results of this study were integrated into presentations, journal articles, and an extension publication to share with producers, agricultural professionals, students, and other researchers. We believe these findings will help farmers in the region align their use of specific cover crop species with portions of their farm or fields where those species will be most beneficial.

• Quantify the biomass production and species composition of cereal rye-crimson clover cover crop mixtures as compared to cereal rye monocultures and winter fallow at different landscape positions.
• Quantify the amount of nitrogen taken up from the soil nitrogen pool and produced through symbiotic nitrogen fixation by a cereal rye-crimson clover winter cover crop mixture at different landscape positions.
• Quantify the rates of decomposition of a cereal rye winter cover crop and a cereal rye-crimson clover winter cover crop mixture at different positions throughout the landscape under a corn cash crop.