Soil Profile Organic Carbon as Affected by Tillage and Cropping Systems.

Reports on the long-term effects of tillage and cropping systems on soil organic carbon (SOC) sequestration in the entire rooting profile are limited. A long-term experiment with three cropping systems [continuous corn (CC), continuous soybean (CSB), and soybean-corn (SB-C)] in six primary tillage systems (chisel, disk, plow, no-till, ridge-till, and subtill) under rainfed conditions in southeastern Nebraska presented such an opportunity. Soil samples were collected to a depth of 150-cm in depth increments of 0 to 15-,15 to 30-, 30 to 60-, 60 to 90-, 90 to 120-, and 120 to 150-cm in the fall of 1999 after harvest, 20 years after the tillage and 14 years after the cropping system treatments were initiated. These samples were analyzed for SOC. Significant differences in total SOC throughout the profile were obtained between tillage and cropping systems. Results of these analyses will be presented and discussed.