Green Manuring-Based Systems and Nutrient Management Interactions Modulate Aggregate CN Stoichiometry, Soil C-Stock, and Crop Yield

Abstract

Chemical-intensive agriculture poses significant threats to human and soil health. One of the primary pathways of soil degradation is the loss of soil organic C through aggregate degradation. However, the long-term interaction effect of diversified cropping systems and nutrient management (NM) options on soil aggregation, associated C accrual, and their regulatory factors remain insufficiently explored. These aspects are important for sustaining the crop productivity and environmental health. Therefore, a long-term fixed-plot experiment (2003–2024) involving organic and conventional NM was undertaken. The individual and interaction effects of green manure (GM)-based cropping systems (i.e., System I: Sesbania aculeata GM-based rotation and System II: Mungbean GM-based rotation) and NM practices were assessed to understand soil C stabilization processes and 5 years' rice–wheat yield dynamics (2019–2020 to 2023–2024) in both systems. Results demonstrated that organic NM promoted the formation of macro- (MaA) and meso- (MeA) aggregates and increased their associated C and N contents. The synergistic interaction between System I (rice–wheat–Sesbania) and organic NM (farmyard manure [FYM] + crop residue [CR] ± biofertilizers [BF]) resulted in significantly higher C accumulation in MaA and MeA compared with conventional chemical NM. Consequently, a higher C preservation capacity was found in MaA and MeA. Notably, passive C (less-labile + nonlabile) accounted for over half of the total entrapped C. In addition, the retention of CR along with organic manures having a high CN ratio enhanced top and subsoil C-stocks. The higher CN ratio of the topsoil larger aggregates was positively correlated with higher C acquisition within aggregates. Based on the findings, long-term organic NM integrating FYM, CR, and BF, coupled with Sesbania green manuring, could be recommended to enhance large-aggregate stability and to promote C and N stabilization within aggregates. This practice could improve soil structure, C-stock and fertility, while sustaining higher rice–wheat productivity.