Intensification of Cereal-Cereal System with Summer Mungbean Changes Carbon Pool with Net Increase in Soil Carbon

Mungbean cultivation in summer fallows within cereal-cereal systems are recommended for sustainable intensification. This study examined the dynamics of lability-graded C-fractions and net C balance following mungbean cultivation across different production ecologies. Three long-term mungbean-inclusive rotations were evaluated: two lowland rice-wheat-mungbean ecologies (LE1 and LE2) and one upland maize-wheat-mungbean ecology (UE). Notably, mungbean cropping resulted in significant changes in active C-pool, while passive C-pool remained unchanged. After mungbean harvest, both LE1 and LE2 showed a reduction in active C-pool (5–12%) and soil organic carbon (SOC) (8–14%). In lowlands, mungbean cultivation led to 16–47% increased active C-pool in sub-surface soil (20–40 cm), contributing to a positive change in C lability index. However, in upland ecology, mungbean cropping did not alter soil C composition. Thus, incorporating mungbean into lowland rice soils of Indo-Gangetic plain (IGP) can enrich active C-pools, particularly in subsurface soils.