Crop Straws with Contrasting C/N Ratios Affect the Organic Carbon Turnover and Its Net Sequestration Efficiency When Solely or Jointly Incorporated to a Fertilized Soil

The quality (carbon to nitrogen ratio; C/N ratio) of crop residue affects the decomposition of soil organic carbon (SOC) due to the nutrient stoichiometry, which requires well-exploration especially on the dynamics and sequestration of SOC in nutrient-sufficient soil. We investigated an 80-day incubation experiment by adding C₃ winter wheat (W) and legume (L) straws (with contrasting C/N ratios) as well as their mixture (W + L) into a C₄ soil that had experienced years of maize planting and fertilization. Either W or L increased the decomposition rate (k_a) of SOC primarily in active pool and released more CO₂ over the short-term incubation. Compared with Ct, the W slightly decreased the k_a, while the L increased the k_a by 49.2% than Ct, and by 75.0% than W. The L increased the straw-derived SOC by 10.6% than W, while it resulted in a higher mineralization of native SOC, which was 2.04 times that of W. The W + L yielded the largest net gain in SOC at 1.35 g kg⁻¹, which followed by the W (0.66 g kg⁻¹) and the L (0.22 g kg⁻¹). Incorporating the lower C/N ratio’s legume straw more stimulated the decomposition of both active and native SOC even in fertilized soil, which could be the most effective at sequestrating SOC when combing with wheat straw. These findings suggest the difference in crop straw should be considered for SOC sequestration potential particularly in response to the increasingly intensified agriculture.