Coal gangue as a sustainable partial substitute for chemical fertilizer: impacts on soil properties, plant growth and crop quality

Background Long-term intensive use of chemical fertilizers leads to soil degradation and nutrient losses, threatening the sustainability of agroecosystems. Coal gangue, rich in mineral nutrients, can be converted into safe and effective fertilizers, offering a potential approach to reduce chemical fertilizer use and recycle industrial solid waste. This study conducted a pot experiment with pak choi seedlings and field experiments with chinese cabbage and cabbage, establishing a gradient of coal gangue fertilizer substitution for chemical fertilizer (0%-100%) while keeping nitrogen levels consistent across treatments. Results Coal gangue substitution for chemical fertilizer significantly altered soil physicochemical properties, with increases in available phosphorus, potassium, total nitrogen, and organic matter observed at specific growth stages. Plant nutrient contents responded differently to coal gangue levels: shoot and root N, P, and K increased in pak choi seedlings and chinese cabbage, whereas cabbage showed more moderate changes, particularly in K content. Coal gangue substitution influenced plant growth traits, enhancing plant height, stem diameter, and biomass accumulation in most cases. Root development was generally promoted, with fresh (a variation of -18.26% to 97.59%) and dry (ranging from -27.25% to 231.26%) weights showing stage- and crop-specific increases. Principal component and Mantel analyses revealed strong correlations between plant biomass and soil/plant traits, indicating that coal gangue substitution modulated the coupling of soil-plant systems. Conclusions Coal gangue substitution for chemical fertilizer improved soil fertility by increasing available nutrients and organic matter, while modulating microbial abundance. It promoted plant growth and root development, leading to higher biomass accumulation, but high substitution levels reduced chlorophyll content and photosynthetic efficiency in cabbage. Organ- and stage-specific effects on nutrient allocation and quality traits, such as nitrate, soluble sugar, protein, and starch, were observed. Overall, coal gangue effectively influenced soil-plant interactions, supporting its potential as a sustainable partial substitute for chemical fertilizer.