Soil organic carbon in managed pastures of the southeastern United States of America

Grazing lands in the southeastern United States of America are managed primarily for introduced plant species that have high forage production potential or that fit in a niche within a farming system. Forages are typically managed with fertilization and grazing pressure on a seasonal basis, depending upon growth habit. Nitrogen (N) application is one of the key determinants of pasture productivity, although its effect on soil carbon (C) sequestration may be minimal, especially considering the associated carbon dioxide (CO2) equivalence costs of fertilization. Fertilization with animal manures is effective and may provide additional soil 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 organic carbon (SOC) 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 with low risk for landowners, improve degraded land by building soil fertility, improve water utilization and quality within the landscape, and help mitigate the greenhouse effect by storing C in soil as organic matter. GRAZING LANDS IN THE UNITED STATES OF AMERICA Grazing lands are extensively distributed throughout the United States (Follett, Kimble and Lal, 2001). The United States Department of Agriculture (USDA) Census of Agriculture for 2007 (http://www.agcensus.usda.gov/) Alan J. Franzluebbers