Organic manure input and straw cover improved the community structure of nitrogen cycle function microorganism driven by water erosion

Water erosion process induces differences to the nitrogen (N) functional microbial community structure, which is the driving force to key N processes at soil-water interface. However, how the soil N transformations associated with water erosion is affected by microorganisms, and how the microbial respond, are still unclear. The objective of this study is to investigate the changes of microbial diversity and community structure of the N-cycle function microorganisms as affected by water erosion under application of organic manure and straw cover. On the basis of iso-nitrogen substitution, four treatments were set up: 1) only chemical fertilizer with N 150 kg ha−1, P2O5 60 kg ha−1 and K2O 90 kg ha−1 (CK); the N was substituted 20% by 2) organic manure (OM); 3) straw (SW); and 4) organic manure + straw (1:1) (OMSW). The results showed that applying organic manure and straw to sloping farmland can increase soil N contents, but reduce runoff depth, Kw, sediment yield and N loss, especially in the OMSW. Straw cover and straw + organic manure increased the diversity (Chao1) of nitrifier (AOB), and both diversity and uniformity (Shannon) of denitrifier (nirK/S) were increased in the OMSW. All erosion control measures reduced N-fixing bacteria diversity and increased their uniformity, and the combined application of organic manure and straw cover was a better erosion control measure than the single application of them. Improved soil chemistry and erodibility were the main drives for the changes of N-functional microbial community structure and the appearance of dominant bacteria with different organic materials.