Opti-BioN

Flooded rice fields lose large amounts of nitrogen as dinitrogen (N2 ), yet the sources of this loss remain unclear. Using a cutting-edge in situ isotopic technique, we show that most N2 emissions arise not from fertilizer, as widely assumed, but from soil organic nitrogen mineralized by fertilization stimulated microbial processes, termed as a microbial nitrogen pump. This hidden pathway highlights a previously overlooked source of soil-derived nitrogen loss, causing conventional methods to overestimate fertilizer-derived losses. Our findings revise nitrogen budgets for rice systems and highlight the need to manage soil–plant–microbe interaction to sustain rice yields while reducing N2 losses. Hybrid rice cultivars markedly lower yield-scaled gaseous nitrogen losses by enhancing plant and microbial nitrogen use efficiency while maintaining high productivity.