Incorporating straw into intensively farmed cropland soil can reduce N2O emission via inhibition of nitrification and denitrification pathways

Abstract

Straw incorporation (SI) combined with N fertilizer has been shown to affect soil N2O emission and N-related functional microbes in agriculture. However, the responses of N2O emission, community structure of nitrifiers and denitrifiers and related microbial functional genes to straw management strategies in the winter wheat season in China remain unclear. Here, we conducted a two-season experiment in a winter wheat field in Ningjing County, northern China, to examine four treatments: no fertilizer with (N0S1) and without maize straw (N0S0); N fertilizer with (N1S1) and without maize straw (N1S0), and their effects on N2O emissions, soil chemical parameters, crop yield, as well as the dynamics of nitrifying and denitrifying microbial communities. We found that seasonal N2O emissions decreased by 7.1–11.1% (p < 0.05) in N1S1 as compared to N1S0, without significant difference between N0S1 and N0S0. In combination with N fertilization, SI increased the yield by 2.6–4.3%, altered the microbial community composition, increased Shannon and ACE indexes, and decreased the abundance of AOA (9.2%), AOB (32.2%; p < 0.05), nirS (35.2%; p < 0.05), nirK (21.6%; p < 0.05) and nosZ (19.2%). However, in the absence of N fertilizer, SI promoted the major genera of Nitrosavbrio (AOB), unclassifiied_Gammaproteobacteria, Rhodanobacter (nirS), Sinorhizobium (nirK), which strongly correlated positively with N2O emissions. Thereby, a negative interaction effect between SI and N fertilizer on AOB and nirS emphasized that SI could offset the increase of N2O emission caused by fertilization. Soil moisture and NO3− concentration were the major factors affecting N-related microbial community structure. Our study reveals that SI suppressed N2O emission significantly and simultaneously decreased the abundance of N-related functional genes and altered denitrifying bacterial community composition. We conclude that SI helps to enhance yield and alleviate fertilizer-induced environmental costs in intensively farmed fields in northern China.