Organic Amendments and Reduced Tillage Accelerate Harvestable C Biomass and Soil C Sequestration in Rice–Wheat Rotation in a Semi-Arid Environment

Rice–wheat crop rotations have high carbon fluxes. A 2-year field study in Punjab, Pakistan quantified impacts of different nutrient management on harvestable carbon biomass, crop-derived C, soil organic C sequestration (SCS), and decomposition. Treatments included different combinations of mineral fertilizer, animal manure (20 Mg ha −1 ), and incorporated crop residue in a split-plot design under conventional tillage (CT) and reduced tillage (RT). Combined use of mineral fertilizer and manure resulted in (1) 12.56% to 53.31% more harvestable C biomass compared to use of fertilizer and manure alone and (2) 18.27% to 60.72% more crop-derived C inputs relative to using only fertilizer or manure across both tillage practices. Combined fertilizer/manure treatments also significantly enhanced SCS relative to using fertilizer alone. Using only manure increased SCS by 63.25% compared with fertilizer alone across both tillage practices. The relationship between SCS and C inputs indicated high humification (14.50%) and decomposition rates (0.46 Mg ha −1 year −1 ) under CT compared to RT at 0–15 cm soil depth. At 15–30 cm soil depth, rates of humification (10.7%) and decomposition (0.06 Mg ha −1 year −1 ) were lower for CT compared to RT. Combined manure/fertilizer treatments could induce high C sequestration and harvestable C biomass with reduced decomposition in rice–wheat rotations.