Combined Application of Organic Materials Improves Soil Properties and Promotes Soil Nitrogen Cycling

ABSTRACT The combined application of organic materials can improve soil performance and crop growth, but the influence of diverse organic materials on soil microbes and nitrogen cycle‐related genes remain obscure. In this study, chemical fertilizer (MC), chemical fertilizer with biochar (MCB), chemical fertilizer with organic fertilizer (MCF), and chemical fertilizer with biochar and organic fertilizer (MCBF) were applied to a field experiment of maize cultivation, and their roles on soil properties, microbial community structure, and nitrogen cycling was determined by metagenomic sequencing technology combined with redundancy analysis (RDA) and correlation analysis. The results showed that pH decreased in co‐application compared with MC, whereas the available nitrogen, phosphorus, potassium, and organic matter (AN, AP, AK, OM) elevated, especially in MCF and MCBF. Crop yield and the content of nitrate and ammonia nitrogen also elevated in both MCF and MCBF, whereas they all decreased in MCB. The phylum Actinobacteria and Proteobacteria were dominant under all treatments. The abundance of hao , nxrB , narG , nirK , norB , nirS , narB , and nosZ increased in co‐application, thereby promoting ammonification, nitrification, and denitrification. The abundance of nasA , napA , nirB , and nifH increased in MCB, but decreased in MCF and MCBF. RDA and correlation analysis revealed that the majority of nitrogen‐cycling genes decreased with pH and increased with other environmental factors. In conclusion, under the premise of guaranteeing yield, the MCBF was the optimal choice to soil quality and nitrogen cycle‐related microorganisms.