Soil carbon sequestration cannot be enhanced efficiently under all‐straw return in cool semiarid regions: Evidences from a long‐term experiment in a crop rotation system.

Crop straw return is one of the most important measures to increase soil organic carbon (SOC) content in farmland systems. However, the effects of crop straw return amount on SOC sequestration (SCS) in long‐term crop rotation system is unclear, especially in typically cool and dry regions. A field experiment was conducted from 2015 to 2020 in a wheat‐maize‐potato rotation system including four straw treatments: without straw incorporation (CK), 1/3 straw incorporation (LS), 2/3 straw incorporation (MS), and all‐straw incorporation (HS), respectively. After 6 years of cropping, SCS in 0–30‐cm soil layer of CK, LS, MS, and HS increased by 3.6, 7.0, 7.8, and 9.9 Mg ha−1, compared with the beginning of the experiment, respectively. In particular, SCS in 20–30‐cm soil layer of CK was obviously increased by 2.7 Mg ha−1. When compared with CK, straw incorporation increased total dry matter, total evapotranspiration, SCS, and water productivity by 29.3%, 3.4%, 28.8%, and 25.2% on average, respectively, but decreased pure carbon accumulation and water use efficiency of carbon sequestration. Although the carbon input and SCS showed a linear positive correlation with evapotranspiration, the carbon input efficiency was negatively correlated with pure carbon accumulation in HS and MS. When compared with LS, the carbon input efficiency decreased by 64.1% in HS, restricting SCS. These results indicated that 1/3 straw incorporation could increase SCS efficiency as well as decrease carbon loss in the–crop system, making it more suitable for application in cool semiarid region, and revealed that excessively straw returning to the field could not improve SCS efficiency. [ABSTRACT FROM AUTHOR]