Elucidating the carbon and nitrogen pools with retention conservative residues and fertility gradients on the legume–maize system

In light of the global climate scenario, this study addresses soil health, with emphasis on stabilizing carbon (C) and nitrogen (N) pools, highlighting the role of legumes as a cornerstone of cropping systems under conservation agriculture. The study evaluated the effects of N gradients and legume biomass incorporation on soil C and N pools in maize ( Zea mays L.), variety DHM-121. The experiment was conducted for 2 years, that is, 2021–22 and 2022–23, in a semi-arid agroecosystem with varying N rates (100, 125, and 150% rate of N) in rabi maize, combined with the incorporation of legume biomass, that is, greengram ( Vigna radiata L.) at 10 t ha −1 . Integrating 150% of N ha −1 with legume biomass significantly increased soil organic C by 25% compared to 100% N, demonstrating potential for C-sequestration under NT. Soil microbial biomass N (SMBN) increased by 30%, and total soil N by 15%, underscoring the synergy between N gradients and legume biomass in enhancing soil fertility. Maize yield was highest in the combined treatment (150% of N ha −1 + greengram biomass), averaging 6.8 t ha −1 , 18% higher than the control. Using 100% N on groundnut crops boosted soil penetration by 25% and aggregate stability by 20%, showing how biomass incorporation can strengthen soil structure for better maize growth. However, the combination of legume biomass X N levels and humus fraction was found to be non-significant. The research shows a novel combination that can be a game changer by integrating 150% N with greengram biomass, which markedly improved soil C, total N, and MBN, demonstrating enhanced soil fertility under no-till maize. The combined treatment also maximized maize yield, highlighting the synergistic effect of N gradients and legume residues. Additionally, legume biomass improved soil structure, indicating its role in sustaining productivity and soil health in semi-arid agroecosystems. The implications are deep for climate-smart agriculture that will deliver for future needs.