CARBON SEQUESTRATION IN RANGELANDS INTERSEEDED WITH YELLOW-FLOWERING ALFALFA (MEDICAGO SATIVA SSP. FALCATA)

Authors: Mortenson, Matthew; Schuman, Gerald; INGRAM, L - UNIVERSITY OF WYOMING

Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2003
Publication Date: 2/1/2004
Citation: Mortenson, M.C., Schuman, G.E., Ingram, L.J. 2004. Carbon sequestration in rangelands interseeded with yellow-flowering alfalfa (medicago sativa ssp. falcata). Environmental Management 33 (Supplement) S475-S481.

Interpretive Summary: Management practices can significantly influence soil carbon storage of rangelands. Previous research has shown that grazing, fire, and fertilization can increase soil carbon storage in mixed-grass, short-grass and tall-grass prairies. At the same time we are interested in management practices that will enhance soil carbon storage, ranchers are also interested in management practices that might enhance forage production and quality. Interseeding yellow-flowering alfalfa into rangelands has the potential to enhance all of these factors: increase soil carbon storage, enhance production, and increase forage quality. Our research assessed rangeland sites that had been interseeded with yellow-flowering alfalfa in 1998, 1987, and 1965. Soil organic carbon was increased by 4, 8, and 17% in the 1998, 1987, and 1965 interseeded pastures, respectively. Nitrogen fixation by the legume also led to increased soil nitrogen levels, hence increased nitrogen (protein) content of the native forages. Forage production was also increased significantly because of the additional nitrogen and the actual production attributed to the alfalfa. Alfalfa accounted for about 1000 kg/ha of increased production on these mixed-grass rangelands in northwestern South Dakota. The practice of interseeding adaptive cultivars of legumes into native rangeland may help to mitigate the elevated atmospheric carbon dioxide levels and at the same time enhance soil quality and sustainability.

Technical Abstract: 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, respectively, 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.