Impact of combined organic amendments and chemical fertilizers on soil microbial limitations, soil quality, and soybean yield

AimsThe combined application of organic amendments and chemical fertilizers is beneficial for the sustainable development of agriculture. Assessing the impact of this integrative approach on rhizospheric soil quality and crop yield, along with their determining factors, is essential for devising appropriate fertilization strategies.MethodsThe long-term field trial, spanning 33 years, includes four treatments: control with no fertilizer (CK), chemical fertilizer only (NPK), chemical fertilizer combined with straw (NPKS), and chemical fertilizer combined with organic manure (NPKM). Assessments were conducted on rhizospheric soil properties, microbial community structure, and extracellular enzyme activity.ResultsThe results indicate that the application of organic amendments significantly enhanced the soil quality index (SQI) by modifying the soil microbial communities. The co-application of straw or organic manure with inorganic fertilizers improved the SQI by 161.9% and 285.7%, respectively, compared to the control. Soybean yields increased by 11.6% with the co-application of organic manure and inorganic fertilizers compared to the use of chemical fertilizers alone. Enzyme stoichiometry scatter plots revealed that all treatments were limited by microbial resource carbon and phosphorus. beta-glucosidase (BG), microbial biomass carbon, and soil organic carbon played pivotal roles in enhancing rhizospheric soil quality. Furthermore, BG, available nitrogen, and microbial biomass phosphorus were critical in determining soybean yield. The nutrient content, biomass, and diversities of bacteria and fungi in the rhizosphere were significantly higher with the combination of organic manure and chemical fertilizers than with conventional fertilization, thereby alleviating the limitations on microbial metabolic carbon and phosphorus.ConclusionsThis study demonstrates that the combined application of organic manure and chemical fertilizers effectively increases nutrient content and improves microbial community structure in the rhizospheric soil. This combination alleviates constraints on microbial carbon and phosphorus metabolism, thereby enhancing soil quality and increasing soybean yield. AVN, TP, and AVP are key factors regulating microbial resource limitations.Organic amendments enhance soil quality through the increased activity of beta-glucosidase (BG).Soybean yield is primarily regulated by BG enzyme activity, AVN and MBP.