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Title: Soil organic carbon in managed pastures of the southeastern USA

item Franzluebbers, Alan

Submitted to: Food and Agriculture Organization of the United Nations Technical Workshop Report
Publication Type: Book / Chapter
Publication Acceptance Date: 1/15/2010
Publication Date: 12/15/2010
Citation: Franzluebbers, A.J. 2010. Soil organic carbon in managed pastures of the southeastern USA [CDROM]. Food and Agriculture Organization of the United Nations Technical Workshop Report.

Interpretive Summary: Soils of the southeastern USA have been historically degraded with intensive cultivation that resulted in loss of topsoil and poor fertility. Pasture management has the potential to build soil fertility, restore soil functions, and mitigate greenhouse gas emissions through surface soil organic matter accumulation. A scientist from the USDA Agricultural Research Service in Watkinsville Georgia summarized recent literature from the southeastern USA on how pastures affect soil organic carbon. Establishment of perennial grass pastures in the southeastern USA can sequester soil organic carbon at rates of 0.1 to 0.5 tons C / acre / year. Soil organic carbon sequestration rate is affected by forage type, fertilization, forage utilization, animal behavior, and soil sampling depth. It can also be spatially affected by animal behavior and by soil depth. Soil organic carbon storage under pastures is important for improving water relations, fertility, and soil quality. With 111 million acres of agricultural land in the southeastern USA, 113 million tons of CO2 / year could be reasonably calculated as potentially sequestered in soil organic matter. Landowners in the southeastern USA have great potential to restore soil fertility and mitigate greenhouse gas emissions with adoption of and improvement in pasture management systems.

Technical Abstract: Grazing lands in the southeastern USA are managed primarily for introduced plant species that have high forage production potential or that fit a niche within a farming system. Forages are typically managed with fertilization and grazing pressure on a seasonal basis, depending upon growth habit. Nitrogen application is one of the key determinants of pasture productivity, although its effect on soil C storage may be minimal, especially considering the C cost of fertilization. Fertilization with animal manures is effective and may provide additional C storage potential, although C may simply be transferred from one ecosystem to another. Moderate grazing of pastures may be the most effective strategy at storing soil C in pastures. Return of dung to the soil surface has positive effects on soil surface properties, including soil microbial biomass and mineralizable C and N. Grazing land managed with a moderate grazing pressure, i.e. utilizing forage to an optimum level without compromising regrowth potential, can provide economic opportunities for landowners with low risk, can improve degraded land by building soil fertility, can improve water utilization and quality within the landscape, and can help mitigate the greenhouse effect by storing C in soil as organic matter.