Nitrogen Fixation in Agriculture, Reducing the Dependency on Chemical Fertilizers

Nitrogen fixation represents a cornerstone of sustainable agriculture, offering an eco-friendly alternative to synthetic fertilizers. While symbiotic fixation in legumes is well-established, growing evidence reveals that interconnective nitrogen fixation in cereal crops can contribute 30–50 kg N/ha/year, complementing legume inputs. This chapter synthesizes recent advances in this field, examining the diversity and mechanisms of nitrogen-fixing bacteria, the regulatory challenges of oxygen sensitivity, nitrogen feedback inhibition, and energy supply. We further evaluate innovative strategies from microbial and plant genetic engineering to optimized agronomic practices designed to enhance fixation efficiency. In the context of climate change, regional fertilizer restrictions, and the urgent need for sustainable intensification, we highlight how emerging technologies in microbiome engineering and synthetic biology are poised to unlock nitrogen fixation for a new era of climate-resilient cropping systems in years to come.