The SOC in the topsoil (0–20 cm) under PM + SL and PM treatments were significantly decreased by 7.10–11.34% from 2010 to 2014 (Fig.1A), but that under CK and SL showed a constant trend. In the 20–40 cm layer, the SOC increased by 25.87–26.32% under PM + SL and SL treatments due to an adequate supply of organic material from the incorporated straw but no significant change was observed under CK and PM (Fig. 1B). The overall SOC under PM + SL and SL treatments in the 0–40 cm soil layer increased by 5.84 and 10.78% (P < 0.05) after 4 years compared with a significant decrease of 6.79% under PM and the little change under CK (Fig. 1C).