Monday, November 5, 2007 - 3:15 PM
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Assessing Potential Soil Organic Carbon Sequestration in Forage-Based Cow-Calf Congregation Sites and Adjoining Pastures.

Gilbert C. Sigua1, Samuel W. Coleman1, and Joseph P. Albano2. (1) USDA-ARS, Subtropical Agricultural Research Station, 22271 Chinsegut Hill Rd., Brooksville, FL 34601, (2) USDA-ARS Horticultural Research Laboratory, Ft. Pierce, FL 34945

Grazing animals have a dominant effect on the movement and utilization of nutrients through the soil and plant system. Grazing can accelerate and alter the timing of nutrient transfers and may increase the amount of nutrients cycled from plants to soils or vice-versa. Our reason for conducting this study is to test whether cattle congregation sites (CCS) typical on most Florida ranches, such as mineral feeders (MF), water troughs (WT), and shade areas (SA) have higher soil organic carbon (SOC) than in other pasture locations. Baseline soil samples around the CCS (MF, WT, and SA) in established (>10 yr), grazed cow-calf pastures were collected in the fall and spring of 2003, 2004, and 2005, respectively. Soil samples were collected from two soil depths (0-20 and 20-40 cm) at different locations around the CCS following a radial (every 90 degrees: North, South, East, and West direction) sampling pattern at 0.9, 1.7, 3.3, 6.7, 13.3, 26.7, and 53.3 m away from the approximate center of MF, WT, and SA. The levels of SOC vary significantly with CCS, distance away from the center of the CCS, sampling depth, and the interaction of CCS and soil depth. Sampling orientations did not significantly affect the levels of SOC. Sampling sites located in shades/trees had the highest level of SOC of 3.58 g/kg, followed by WT sites (3.47 g/kg) and MF sites (2.98 g/kg). The levels of SOC (averaged across CCS) near the center (0.9 m) of the CCS was about 3.29 g/kg compared with 3.17 g/kg SOC at the furthest site (53.3 m). The average SOC of 4.16 g/kg in surface soil (0-20 cm) was significantly higher than that of the subsoil (20-40 cm) with mean SOC of 2.47 g/kg.