Combination of water-saving irrigation and controlled-release fertilizer application reduced gaseous nitrogen loss in single-crop paddy soil.

Through a paddy soil column experiment, we comprehensively evaluated the effects of three irrigation practices and three nitrogen (N) fertilizer application strategies on NH volatilization, NO emissions, and rice yields during the rice growing season to identify the optimal irrigation and fertilization combination technique to reduce both NH and NO losses in paddy soil while sustaining rice yield. In addition, we integrated molecular biology techniques (Quantitative PCR) to establish correlations between environmental factors and the abundance of N cycling-related soil microbial functional genes, revealing the intricate interactions between NH volatilization and NO emissions under varied coupling irrigation and fertilization schemes. Our results clearly showed a trade-off relationship between NO and NH emissions under water-saving irrigation practices (controlled irrigation (CI) and intermittent irrigation (II)) coupling with traditional fertilizer urea. Compared with continuous flooding (CF) practice, both CI and II treatments reduced NH volatilization by 36.3-73.9%, while increasing NO emissions by 1483.2-2246.2% during the rice growing season. Notably, the combination application of CRF under CI mode (CI-CRF) significantly reduced NH volatilization by 65.0% during the rice growing season, compared to the conventional II-Urea approach. Although the impact on NO emissions was modest, CI-CRF strategy still achieved a 4.6% reduction in NO emissions, thus tackling the trade-offs between two important environmentally damaging gases under water-saving irrigation. The suppression of NH volatilization was primarily attributed to the CI-CRF strategy lowering NH-N concentrations in flooding water, while the reduction in NO emissions was associated with an increase in soil nirS and nosZ gene abundances. Further estimates indicated that the CI-CRF strategy could potentially reduce NH volatilization by 259.2 Gg N yr and NO emissions by 3.1 Gg N yr in single-crop paddy field in China, compared with traditional II-Urea approach. Therefore, the optimal reduction of gaseous N loss, coupled with yield enhancement, could be achieved through the synergistic strategy of CI-CRF in single-crop rice cultivation ecosystems. Future studies should focus on field-based experiments that explore the long-term effects of CI-CRF combinations under varying soil types, climates, and rice cultivation systems.