Long-term Effects of Partially Substituting Chemical Fertilizers with Different Organic Amendments

The long-term effects of different organic soil amendments remain unclear. In this study, a 9-year field experiment was conducted in Shandong Province, China, to evaluate the impacts of different organic amendments on apple yield, soil physicochemical properties, and microbial community structure. The results indicated that partial substitution of chemical fertilizers with bio-organic amendments mitigated soil acidification, increased soil organic matter content and nutrient content, enhanced the proportion of water-stable aggregates, improved overall soil physicochemical properties, and optimized soil microbial community structure. Redundancy and correlation analyses revealed layer-specific relationships. At the 0–20 cm soil layer, the relative abundance of Actinobacteriota was significantly positively correlated with soil electrical conductivity (EC). In contrast, the relative abundances of Gemmatimonadota and Pseudomonadota were both significantly negatively correlated with soil EC. At the 20–40 cm layer, the relative abundances of Acidobacteriota , Basidiomycota , and Ascomycota were significantly positively correlated with the content of water-stable large aggregates. These results hold significant theoretical implications for the research and promotion of various types of organic amendments.