Changes in grassland management intended to increase productivity can lead to sequestration of substantial amounts of atmospheric C in soils. Management-intensive grazing (MiG) can increase forage production in mesic pastures, but potential impacts on soil C have not been evaluated. We sampled four pastures (to 50 cm depth) in Virginia, USA, under MiG and neighboring pastures that were extensively grazed or hayed to evaluate impacts of grazing management on total soil organic C and N pools, and soil C fractions. Total organic soil C averaged 8.4 Mg C ha–1 (22%) greater under MiG; differences were significant at three of the four sites examined while total soil N was greater for two sites. Surface (0–10 cm) particulate organic matter (POM) C increased at two sites; POM C for the entire depth increment (0–50 cm) did not differ significantly between grazing treatments at any of the sites. Mineral-associated C was related to silt plus clay content and tended to be greater under MiG. Neither soil C:N ratios, POM C, or POM C:total C ratios were accurate indicators of differences in total soil C between grazing treatments, though differences in total soil C between treatments attributable to changes in POM C (43%) were larger than expected based on POM C as a percentage of total C (24.5%). Soil C sequestration rates, estimated by calculating total organic soil C differences between treatments (assuming they arose from changing grazing management and can be achieved elsewhere) and dividing by duration of treatment, averaged 0.41 Mg C ha–1 year–1 across the four sites.
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We wish to thank Nasheed Smith, Jen Carter, and Sarah Moculeski for assistance in processing and analyzing soil samples. Thanks also to Rick Feete, Alan Graybeal, Gerry Rider, Billy Wayson, and Irvin White for graciously allowing us to collect soil samples in their pastures. Glenn Johnson was instrumental in identifying willing producer participants. Thanks to Jim Hammons, Mark Alley, and the Department of Crop and Soil Environmental Sciences at Virginia Polytechnic Institute and State University for field assistance and use of their Giddings rig. Jeannine Freyman, Louis W. Heidel, and Jim Sawyer assisted with collection of soil samples. This research was funded by grant 826499-01-0 from the Environmental Protection Agency and grant DE-FG03-00ER62997 from the Department of Energy. The comments of three anonymous reviewers are appreciated.
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Conant, R.T., Six, J. & Paustian, K. Land use effects on soil carbon fractions in the southeastern United States. I. Management-intensive versus extensive grazing. Biol Fertil Soils 38, 386–392 (2003). https://doi.org/10.1007/s00374-003-0652-z
- Carbon sequestration
- Grazing management