SOIL ORGANIC CARBON ASSOCIATED WITH PASTURE LAND IN THE UPPER PIEDMONT OF SOUTH CAROLINA

Sustained soil quality is crucial for agricultural practices around the world. Globally, soil erosion has led to increased organic matter oxidation and decreased soil organic carbon (SOC), with 50% soil carbon erosion over the past 50 years. Soil organic carbon is valuable because it improves water retention, retains nutrients, and develops soil structure. Poor management practices across the South Carolina piedmont have led to severe soil erosion and loss of SOC. The purpose of this study was to examine spatial variability of SOC among pastures and with depth across six sandy or clay loam Ultisol series at a 75 ha farm in Pickens County, SC. Farm management included intensive grazing practices and varied crop cover among pastures. A stratified random sampling method identified 150 locations to collect a 60 cm soil core and 20 cm soil profile. Gravimetric loss on ignition (LOI) was used to estimate SOC concentration of 2032 individual samples. Horizon depths, color, and texture were described for profiles at each site. We found significant differences in LOI of the top 10 cm among the six Ultisol series. Percent LOI was highest in Hiwassee sandy loam (9.1 ± 2.3%) and lowest in Tallapoosa sandy loam (5.9± 1.9%). Slope geomorphology was a control on percent LOI in the top 10 cm. Hiwassee sandy loams were found on foot-slopes, which tended to accumulate SOC during erosive events, whereas Tallapoosa sandy loam was an upland soil with higher erosion vulnerability. Land use history determined the LOI depth profile. In pastures which were historically cultivated, most of the cores showed high LOI at the surface that decreased with depth. This decrease was followed by an abrupt increase of 5-10% LOI at a depth between 15 and 25 cm, followed by another decrease to < 5% LOI. In contrast, for pastures that were recently deforested, LOI started high and decreased to <5% LOI at depth. Increased LOI at depth is interpreted to represent a plow line below which crop roots accumulated in historically cultivated pastures. Observations of roots at depth validate this interpretation. Recently deforested pastures lack the plow line. The findings of this study will be used as a baseline for future SOC studies of the same farm to determine how management practices influence temporal increases in SOC.