162 Grazing land management and soil texture as determinants of soil organic carbon storage.

Abstract Soil is a large reservoir of organic carbon. This reservoir provides a source and sink for CO2 exchange with the atmosphere. Organic matter, of which ~58% is carbon, contributes in unique ways to the physical, chemical, and biological characteristics of soil. These characteristics give soil its ability to provide a diversity of functions upon which our planet depends. Stocks of soil organic carbon are constrained by a variety of factors, including climatic conditions (temperature, precipitation, wind), soil texture, landscape position, and land management. This evaluation focuses on the effects of soil texture and grazing land management on soil organic carbon in the southeastern US, a warm-humid environment. Although many reports focus on clay concentration, it is the sand fraction of soil that has the most direct influence on the stock of soil organic carbon and nitrogen. The type of forage, harvest utilization strategy, stocking rate, stocking method, fertilization, and external organic inputs can alter soil organic carbon and nitrogen but not necessarily in the same way or magnitude in all environments. This presentation describes available evidence to support appropriate grazing land management for sustainable livestock production.