Legume Inclusion in Wheat Rotations Increases Long‐Term Soil Carbon Storage via Carbon Management Indices and Microbial Stoichiometry

Long‐term crop rotations influence soil organic carbon (SOC) dynamics and microbial nutrient balance, both of which are critical for sustaining soil fertility. This study evaluated SOC storage, microbial biomass stoichiometry, and carbon management indices across three long‐term (≥ 10 years) cropping systems: wheat–rice (W–R), wheat–maize (W–M) and wheat–legume (chickpea) (W–L). The W–R system was used as a reference, as it represents the most traditional cereal‐based rotation in the region. Results showed that SOC storage increased by 45% and 29% in the wheat–legume and wheat–maize cropping systems, respectively, compared to the wheat–rice plot. Permanganate oxidizable carbon and the carbon management index were 64%–65% and 37%–38% higher, respectively, in the legume‐based system relative to maize and rice rotations. The carbon stability index did not differ significantly among the cropping systems. Cumulative SOC mineralization increased by 32% and 14% in W–L and W–M, respectively, compared to W–R. The microbial metabolic quotient was elevated in W–L and W–M, reflecting increased availability of labile carbon. Long‐term legume inclusion also significantly increased microbial biomass carbon and nitrogen, while narrowing microbial and soil C:N:P stoichiometry relative to W–M and W–R. These shifts highlight the role of nitrogen‐fixing legumes in promoting microbial activity, nutrient availability and carbon sequestration. Overall, these findings demonstrate that legume inclusion in wheat‐based rotations significantly increases long‐term SOC storage through improvements in carbon management indices and microbial stoichiometry, relative to the traditional W–R system. The consistent enhancement of microbial nutrient balance and labile carbon fractions highlights the potential of cereal–legume systems to improve soil quality and support sustainable intensification. Future research should evaluate the scalability of these benefits across diverse soil types and examine their long‐term implications for nutrient cycling, yield stability and agroecosystem resilience under variable climatic conditions.