Potential of Biofertilizers in Mitigating Nitrous Oxide Emissions from Rain-Fed Rice Cultivation in the Lower Brahmaputra Valley of Assam, India

Chemical fertilizer application in rice farming generates nitrous oxide (N2O), a powerful greenhouse gas that contributes to global warming and climate change. A two-year study was undertaken to compare N2O emissions from rain-fed rice treated with five different chemical and biofertilizer combinations, namely, T1: NPK100 (100% recommended NPK or control); T2: NPK50 + AZT (50%NPK + Azotobacter); T3: NPK50 + AZS (50%NPK + Azospirillum); T4: NPK50 + PSB (50%NPK + Phosphate Solubilizing Bacteria); and T5: NPK50 + AMF (50%NPK + Arbuscular Mycorrhizal Fungi). Cumulative seasonal N2O emissions from the treatments ranged from 119.66 to 261 mg N2O-N m−2 in 2021 and from 61.01 to 187.41 mg N2O-N m−2 in 2022. Approximately 32–67% reductions in cumulative emissions were achieved with biofertilizer applications over NPK100. NPK50 + AZT and NPK50 + AMF were identified as low-N2O-emitting treatments, while NPK50 + AZS and NPK50 + PSB were intermediate-emitting with respect to NPK100. Beneficial effects of biofertilizer applications on soil organic carbon storage, root biomass, leaf chlorophyll content and nitrogen use efficiency were noted, which likely contributed to greater yields and reduced global warming potentials. NPK50 + AZT and NPK50 + AMF significantly improved yield attributes, grain carbohydrate content and rice yield over NPK100, suggesting that biofertilizers can reduce chemical fertilizer requirements in rice cultivation.