Effects of straw incorporation on biological nitrogen fixation under continuous and intermittent flooding irrigation in a rice cropping system

Both straw incorporation and irrigation practices affect biological nitrogen （N） fixation （BNF）,but it is still unclear how straw incorporation impacts BNF under continuous （CFI） or intermittent （IFI） flooding irrigation in a rice cropping system.A15N2-labeling chamber system was placed in a rice field to evaluate BNF with straw incorporation under CFI or IFI for 90 d.The nif H （gene encoding the nitrogenase reductase subunit） DNA and c DNA in soil were amplified using real-time quantitative polymerase chain reaction,and high-throughput sequencing was applied to the nif H gene.The total fixed N in the straw incorporation treatment was 14.3 kg ha-1under CFI,being 116% higher than that under IFI (6.62 kg ha-1).Straw incorporation and CFI showed significant interactive effects on the total fixed N and abundances of nif H DNA and c DNA.The increase in BNF was mainly due to the increase in the abundances of heterotrophic diazotrophs such as Desulfovibrio,Azonexus,and Azotobacter.These results indicated that straw incorporation stimulated BNF under CFI relative to IFI,which might ultimately lead to a rapid enhancement of soil fertility.