Tuesday, February 6, 2007

Soil Organic Carbon Across a Coastal Plain Landscape: Effects of Tillage and Crop Management Systems.

Jeffrey Novak1, James Frederick2, P. J. Bauer3, Susan R. Griggs4, and Don Watts1. (1) USDA-ARS-Coastal Plains Research Center, 2611 W. Lucas Street, Florence, SC 29501-1241, (2) Clemson University, Pee Dee Research & Education Center., 2200 Pocket Road, Florence, SC 29506-9706, (3) USDA-ARS, Coastal Plains Soil, Water, and Plant Research Center, 2611 W Lucas Street, Florence, SC 29501, (4) Clemson University, Pee Dee Research and Education Center, 2200 Pocket Road, Florence, SC 29506-9706

Effective employment of conservation tillage (CT) and crop management practices to obtain significant amounts of C sequestration will require an understanding of quantitative relationships between crop residue inputs under different rotations and potential changes in soil organic carbon (SOC) content.   A field study was initiated in the late 1990’s to compare cropping system effects (centered on surface tillage) on SOC levels and to establish relationships between crop residue inputs with changes in SOC contents.   A 7-ha field that contained well-drained upland soils and a depressional area composed of several poorly drained soils was divided into two 3.5-ha fields.  Between 1998 and 2005, both fields were under a 1 yr rotation of winter wheat (Triticum sp.) and soybean (Glycine max, L.), which was followed by 3 yrs of a corn (Zea Maze L.) cotton (Gossypium hirsutum L.) rotation plus 1 additional yr of cotton.  One field was tilled using disk tillage (DT) and the other using CT.  Annual soil samples at 0 to 3-cm and 3 to 15-cm depths, along with bulk density and crop residue samples were collected from both fields.  When averaged across each field, significant differences in SOC contents in the soil under CT occurred after 7 yrs of management.  A significant change in SOC content (+0.88 Mg/ha) only occurred at the 0 to 3-cm soil depth.  Summed over 8 yrs, the CT produced 20.68 Mg/ha of organic carbon as crop residue; less than 5% was incorporated into the SOC pool.  Results from this study show that only a small portion of the organic carbon from crop residue inputs will be incorporated into the SOC pool, however, over the long-term, this can result in a significant SOC increase in the top few cm of soil.