Positive effects of organic fertilizers and biofertilizers on soil microbial community composition and walnut yield

Different fertilization regimes differentially impact the physicochemical properties, diversity, and ecosystem functioning of soil microbial communities. However, there is little research on the relationship between soil quality, microbial diversity, and crop production under different long-term fertilization regimes, especially on woody plants. Therefore, in this study, we investigated changes in the soil microbial communities of walnut orchards after nine years of continuous fertilization (no fertilizer, only chemical fertilizer, chemical + organic fertilizer, chemical + biofertilizer, and chemical + organic + biofertilizer), and analyzed the link between fertility improvement and yield increase from a microbial perspective. The results showed that the soil quality index was strongly correlated with organic fertilizers and biofertilizers addition, and exhibited a significant relationship with walnut yield. Furthermore, the addition of organic fertilizers or biofertilizers promoted the enrichment of microorganisms beneficial to soil fertility, crop growth ( Bacillus spp.) and soil bioremediation ( Solicoccozyma spp.) and decreased the amounts of Fusarium spp. in the walnut orchard soil. Moreover, structural equation modeling indicated strong and positive relationships between walnut yield and the diversity of the keystone microbial communities. Overall, the results confirm the feasibility of using multiple fertilizer blends to improve soil fertility and reveal the fundamental role of fungal diversity in maintaining economic forest tree production. • Long-term fertilization dramatically altered soil microbial community composition. • SEM was used to evaluate the link between microbial diversity and walnut yield. • Biofertilizer boosts microbes beneficial to soil fertility and crop growth. • It is preferable to combine multiple fertilizers for walnut plantation management. • Fungal diversity plays a key role in maintaining economic forest tree production.