308-3 Short-Term Effects of Grazing Intensity and Nitrogen Fertilization On Soil Organic Carbon Under Grazed Pastures In the Southeastern USA.



Wednesday, October 19, 2011: 10:35 AM
Henry Gonzalez Convention Center, Room 217C, Concourse Level

Maria Lucia Silveira1, Kesi Liu2, Lynn Sollenberger3 and Joao Vendramini1, (1)University of Florida, Ona, FL
(2)University of Florida, Gainesville, FL
(3)Agronomy, University of Florida, Gainesville, FL
Pasture management can have important implications on the amounts and long-term stability of soil organic carbon (SOC). We investigated short-term impacts of grazing intensity and N fertilization levels on C dynamics in various SOC pools in a warm-season perennial grass pasture grown on a Florida Ultisol. Treatments consisted of three grazing intensities (based on target stubble height of 8, 16, and 24 cm) and three N fertilization levels (250, 150, and 50 kg N ha-1). Soil samples (0 to 20 cm) were collected from each pasture prior to the initiation (Spring 2006) and at the end of the 2-yr study (Fall 2007). Grazing intensity and N levels had no effect on bulk soil total C and N concentration and content. Increasing stubble height and N level resulted in a linear increase in C and N concentration in the <53 μm particle-size fraction. Grazing intensity showed a significant effect on δ13C values in the < 53 μm fraction. 13C values in the < 53 μm fraction were depleted as grazing intensity increased, indicating that the readily decomposable C components (C4-derived C) were lost in response to intensive grazing. The < 53 μm particle-size fraction proved to be an earlier indicator of the consequences of management strategies than did total SOC. Further studies are warranted to examine long-term impacts of grassland management on soil C pools in sandy soils of subtropical regions.

 

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Management Impact On GHG Emissions and Soil C Sequestration: II