Management Intensification Impacts on Soil Carbon Dynamics in Subtropical Grazing Lands.

Native and improved grazing lands are a significant sink for long-term C sequestration as they contain and 10 to 30% of the world’s soil C reserves (Eswaran et al. 1993; Schimel, 1995). Because grazing lands occupy a vast area throughout the world, small changes in the amounts of C stored in this ecosystem can have significant consequences in the overall C cycle and atmospheric CO₂ levels. Reports have shown that an increase (or loss) of only 1% of the soil C in the top 4 inches of grazing land soils is equivalent to the total C emissions from all U.S. cropland agriculture (Follett et al. 2001). This trend underscores the importance of grazing lands to mitigate at least part of global atmospheric CO₂ emissions. However, soil organic C accumulation in grazing lands is strongly influenced by management. Current management strategies (e.g., fertilization, and grazing management) are generally aimed at increasing forage production to match animal stocking rates or forage demand from hay. However, grazing land management controls organic matter production, distribution and quality and, therefore, has major effects on C sequestration and greenhouse gas emissions. Research has shown that fertilization, grazing management, and changes in vegetation composition can have major impacts on soil C accumulation. Properly-managed grazing lands generally maintain or even increase soil C accumulation compared with native ecosystems. Although opportunities for increasing soil C sequestration in response to management practices vary in intensity and are specific to each ecosystem, adoption of sustainable management practices that favor C inputs and minimize decomposition are the key to increase C sequestration in grazing land soils. In addition, increasing soil C accumulation can also have significant impacts on the overall soil quality and can potentially contribute to the sustainability of grazing land ecosystems in the U.S.