Long-Term Land-Use Effects On Soil Organic Carbon Sequestration.

Soils sequester large amounts of atmospheric carbon dioxide (CO2) in the soil organic carbon (SOC) pool. Soil carbon (C) sequestration implies increase in the pool of organic compounds with long mean residence time (MRT) over time per unit land area. However, major unknowns in the terrestrial C cycle are whether land use and management affect the MRT of SOC, and how SOC sequestration in soil profiles can be strengthened to mitigate atmospheric increases in CO2 and adapt to the projected climate change. Thus, the objectives of this study is to compare the amount and stabilization of the SOC pool to 0.5-m depth in soil profiles at long-term forest, pasture and no-till corn (Zea mays L.) plots at the North Appalachian Experimental Watershed (NAEW), Coshocton, Ohio. The data from the long-term field experiment show that the SOC pool in forest soil is 28.5, 13.2, and 16.9 Mg C ha-1 in 0-15, 15-30, and 30-50 cm depths, respectively. Similarly, SOC pool in pasture soil is 37.5, 15.2, and 9.3 Mg C ha-1, and that under no-till corn is 28.1, 16.8, and 11.2 Mg C ha-1 in 0-15, 15-30, and 30-50 cm depths, respectively. These data indicate that pasture stored more SOC than no-till corn and forest (62.0 vs. 56.1 and 52.9 Mg C ha-1, respectively) to 0.5-m depth. However, only 21% of the SOC pool to 0.5-m depth under pasture was chemically stabilized as indicated by oxidation with disodium peroxodisulfate (Na2S2O8). In contrast, 25% and 27% of the SOC pool under forest and no-till corn, respectively, was resistant to oxidation with Na2S2O8. Thus, although pasture can store more SOC than soil under other land uses, the higher percentage of labile SOC may enhance the positive feedback of the SOC pool to the atmosphere under pasture in response to climate change.