Decoding belowground links and fertility indicators: Soil drivers, carbon components, microbes, and crop yield under long-term organic (vermicompost) and inorganic nutrient (urea) fertilizer

Background and Aims This 11-year study investigated the relationship between chemical drivers affecting soil microbial community structure, plant function, and yield under different fertilizer regimes (control, urea, vermicompost, and their combination) in a wheat-maize rotation system, aiming to enhance soil fertility and health. Methods The treatments in this study included six levels of fertilization: control (CO), standard rate (SV), double standard rate with vermicompost (DV), standard rate with urea (SU), double standard rate with urea (DU), and a combined application of SU and SV (HSU+HSV). Results Treatments receiving vermicompost (V) led to increases in low labile organic carbon (LOC) and recalcitrant organic carbon (ROC) compared to urea treatments (U). The proportion of high labile organic carbon (LOC-H) and medium labile organic carbon to SOC depended on carbon input through crop residues, roots, and exudates in CO, DU, and SU treatments. Replacing U with V enhanced negative gram bacteria (BaG-) performance by providing higher access to nutrients, a balanced SOC ratio, and decreased pH. Applying U increased fungal biomass and reduced positive gram bacteria biomass (BaG+), indicating fungi's higher sensitivity to N compared to C. Mycorrhizal fungal biomass and Shannon microbial diversity index decreased under DU conditions compared to CO. Conclusion Long-term vermicompost application improved soil quality by increasing SOC components and stocks, enhancing microbial activity, nutrient availability, and plant yield. The combined use of urea and vermicompost led to a beneficial symbiosis, regulating soil functions and plant properties, ultimately enhancing soil fertility and health in the wheat-maize rotation.