Biochar amendment has stronger effects than fertilizer regimes on the bacterial community structure and ecological processes in broomcorn millet field on the Loess Plateau

Aims The application of biochar amendments or organic manure substitutions can alleviate the harmful environmental effects of inorganic fertilizers on agroecosystems, whereas they can also affect soil microenvironments which have not been fully explored on the Loess Plateau. Methods Our field experiments consisted of no fertilizer (N0), N application (150 kg N hm −2 , N150), 30% organic manure replacing N fertilizer (NO30), no fertilizer plus 10 t hm −2 biochar (N0 + C), N application plus 10 t hm −2 biochar (N150 + C), and 30% organic manure replacing N fertilizer plus 10 t hm −2 biochar (NO30 + C). The nutrient levels, bacterial community structure, ecological network, assembly process of bulk soil and rhizosphere at jointing and flowering stages, and crop yield in broomcorn millet field were investigated. Results Fertilizer regimes and biochar amendments increased the bulk soil and rhizosphere nutrient contents than no fertilizer and no biochar. NO30 significantly improved the rhizosphere observed OTUs at jointing and flowering stages. Biochar amendments increased the observed OTUs of bulk soil and rhizosphere than no biochar. N150 and NO30 had a lower network complexity than N0 treatment, whereas N150 + C had the most complex network. Biochar amendments had more deterministic process than fertilization regimes. Meanwhile NH 4 + -N content was the major factor shaping the bacterial diversity, structure, and assembly process. NO30 + C has the highest yield of broomcorn millet. Conclusions Compared with fertilizer regimes, biochar amendment had higher nutrient contents and observed OTUs of bulk soil and rhizosphere, and it also had a more substantial influence on the bacterial community structure and network stability.