Carbon Sequestration in Rangelands Interseeded with Yellow-Flowering Alfalfa (Medicago sativa ssp. falcata)

Management practices can significantly influence carbon sequestration by rangeland ecosystems. Grazing, burning, and fertilization have been shown to increase soil carbon storage in rangeland soils of the Great Plains. Research was initiated in 2001 in northwestern South Dakota to evaluate the role of interseeding a legume, Medicago sativa ssp. falcata, in northern mixed-grass rangelands on carbon sequestration. Sampling was undertaken on a chronosequence of sites interseeded in 1998, 1987, and 1965 as well as immediately adjacent untreated native rangeland sites. Soil organic carbon exhibited an increase of 4% in the 1998, 8% in the 1987, and 17% in the 1965 interseeding dates compared to their respective native untreated rangeland sites. Nitrogen fixation by the legume led to significant increases in total soil nitrogen and increased forage production in the interseeded treatments. Increases in organic carbon mass in this rangeland ecosystem can be attributed to the increase in soil organic carbon storage and the increased aboveground biomass resulting from the increased nitrogen in the ecosystem. The practice of interseeding adaptable cultivars of alfalfa into native rangelands may help in the mitigation of elevated atmospheric carbon dioxide and enhance the long-term sustainability of the ecosystem.