Flooded rice paddies host diverse nitrogen-fixing microorganisms that can convert atmospheric nitrogen into forms available to plants, offering a potential complement to synthetic nitrogen fertilizers. In this review, Yanhui Zhang, Haihou Wang and Peifeng Chen examine how biological nitrogen fixation (BNF) operates in rice (Oryza sativa) ecosystems, the environmental and agronomic factors that regulate it, and opportunities to strengthen this natural process to support more sustainable rice production.

Drawing on published research, the review examines methods for measuring BNF, the distribution and activity of nitrogen-fixing microorganisms, and the effects of soil conditions, rice varieties, water management and fertilizer application. Evidence from rice paddies in China indicates that nitrogen fixation is spatially concentrated in surface soil layers, where cyanobacteria are important contributors, while diverse heterotrophic microorganisms operate in the rhizosphere and deeper soil. The review also highlights a key challenge: synthetic nitrogen fertilizers can strongly suppress BNF, limiting the contribution of this process to soil fertility and nutrient supply.

Proposed strategies include incorporating rice straw to provide organic carbon, optimizing fertilizer rates, timing and placement, and selecting nitrogen-fixing microorganisms that tolerate higher nitrogen availability. Genetic engineering to develop bacteria that release fixed nitrogen is also discussed as a potential approach requiring further validation. The authors emphasize important knowledge gaps, including the need for long-term field measurements and assessments across different rice-growing regions and water regimes. The review provides a scientific basis for evaluating how biological nitrogen fixation could help improve nitrogen-use efficiency, reduce dependence on synthetic fertilizers and support soil health, while recognizing that field-scale benefits remain context-dependent.