Long-term cereal-legume intercropping accelerates soil organic carbon loss in subsoil of dryland

Subsoils are important reservoirs affecting soil organic carbon (SOC). However, little is known about the factors controlling SOC pools in subsoils, and the response of SOC stability to sustainable cropping patterns (e.g., intercropping) remains to be determined. A 10-year experimental field experiment data indicated that cereal–legume intercropping improved net yield gain averagely by 2.2–4.9 t ha-1. SOC storage increased in the topsoil but declined significantly by 5.3% in the subsoil. The increase in soil nitrogen (13.3%) across soil profile resulted in 14.5% decrease in soil C/N. Unexpectedly, microbial growth was evidently stimulated, thereby accelerating SOC decomposition. Interestingly, this process also contributed to the stability of the existing SOC pool. Our results suggest that the adoption of intercropping indeed can improve land use efficiency at a relatively long time scale, but its functional role in subsoil C storage and stability needs to be reconsidered.