Nitrogen-fixing cyanobacteria have the potential to improve nitrogen use efficiency through the reduction of ammonia volatilization in red soil paddy fields.

Nitrogen-fixing cyanobacteria (NFC) biofertilizers have demonstrated great potential in improving rice yield and soil fertility. However, few studies have systematically evaluated the effects of combined application of NFC biofertilizers and chemical nitrogen (N) fertilizer on ammonia (NH 3) volatilization and rice N absorption in red soil paddy fields. Therefore, we conducted a 2-year single cropping paddy field study to determine the NH 3 volatilization loss from paddy soil, as well as rice yield and N use efficiency (NUE). The experiment designed five treatments, including one control (CK, no N applied) and four experimental treatments (N100, complete application of chemical N fertilization; RN50, replacing half of chemical N fertilizer with NFC; RN100, complete replacement of chemical N fertilizer with NFC; N50, only half application of chemical N fertilizer) based on different chemical N fertilizer and NFC biofertilizers application ratios. The results showed that the average cumulative NH 3 volatilization losses of RN50 and N50 treatments were reduced by 41.63% and 45.34% than that of N100 treatment, respectively, mainly due to the reduction of ammonium N content in the overlying water and topsoil. The average NUE of RN50 and N50 treatments were 57.85% and 48.49%, which were 43.83% and 20.56% higher than that of N100, respectively. Path analysis results showed that the application of NFC increased the total soil N content and mitigated the volatilization of NH 3 , which increased the residence time of N in the paddy field, thereby increasing the NUE of rice. The average rice yield of RN50 was 5603.85 kg ha−1, which was not significantly different from N100, but 18.62% higher than N50. Although RN100 elevated NUE and reduced NH 3 volatilization, its grain yield was significantly lower than that of N100. These results suggest that the replacement of an appropriate proportion of chemical N fertilizer with NFC could be a promising approach to mitigating NH 3 volatilization, enhancing rice NUE, and maintaining rice yield in red soil paddy fields. • Application of nitrogen-fixing cyanobacteria (NFC) reduced ammonia (NH 3) emissions. • Application of NFC can enhance nitrogen use efficiency in red soil paddy fields. • NFC moderate replacement of chemical nitrogen fertilizer can maintain rice yield. [ABSTRACT FROM AUTHOR]