Abstract:Soil carbon plays an important role in maintaining the productivity and yield stability of crops and regulating global climate change. The changes in soil carbon were affected by lots of factors, such as climate, environment and agricultural management measures. In order to study the effects of long-term conservational tillage measures on soil carbon pool and stability, we collected soils (0-200 cm depths) in farmland after 16 years of traditional tillage (T), traditional tillage + straw (TS), no tillage (NT) and no tillage + straw (NTS) treatments in maize (Zea mays L.) - wheat (Triticum aestivum L.) - common vetch (vicia sativa L.) rotation system on the Loess Plateau, China. We analyzed the changes in soil organic carbon (SOC), total carbon (TC), readily oxidized organic carbon (AOC) Content and soil carbon pool index (CPI), carbon pool management index (CPMI), and soil carbon pool activity index (AI). We found that 16 years of conservational tillage measures increased soil OC and AOC Content in the 0-5 cm soil depth, but had no effects at 5-200 cm depth. When compared with T treatment, TS, NT and NTS increased soil OC contents by 59.74%, 58.43% and 80.56%, respectively, and increased AOC contents by 49.80%, 49.56%, 53.17%, respectively. The effects of conservational tillage measures on soil carbon stability varied with soil depths, for example, the CPI was significantly higher in 0-10 cm soil depth than that in 10-20 cm soil depth; while the higher AI and CPMI were found in 10-20 cm soil depth. In addition, the AOC and CPI, AI, CPMI were significantly correlated, implying the changes in AOC contents were the main reason for the changes in soil carbon pool stability. The results from this study suggested that no tillage + straw was an effective measure to improve surface soil carbon pool and the stability in farmland.