The addition of spent oyster mushroom substrates has positive effects on alfalfa growth and soil available nutrients

This study aimed to investigate the effects of spent mushroom substrate (SMS, 0%, 10%, 20%, and 30%, w/w) addition to degraded grassland soil on the growth and nutrient uptake of alfalfa through a greenhouse pot experiment. Meanwhile, we compared with the inorganic fertilizer (CF, 200 N mg/kg and 30 P mg/kg) application treatment, and explored the most suitable SMS addition amount for alfalfa yield. Our results showed that compared with the control treatment (CK), 10%SMS, 20%SMS, 30%SMS, and CF treatments increased alfalfa shoot biomass by 1.19, 1.67, 1.77, and 1.77 times, respectively. Total carbon in leaves and total nitrogen contents in stems of 20%SMS treatment were significantly higher than other treatments. Adding SMS increased the nodule number, especially the 20%SMS treatment. In addition, the concentrations of dissolved organic carbon, available phosphorus, and microbial biomass carbon and nitrogen were significantly enhanced with increasing SMS addition, and there was no significant difference between CF and CK treatments except for available phosphorus. Shoot biomass was significantly correlated with available phosphorus. In summary, adding SMS (20% and 30%) to degraded grassland soil can significantly improve soil nutrients and microenvironment to increase alfalfa yield, but considering economic benefits, 20%SMS is the most suitable application amount. This study provides the theoretical basis and technical support for the large-scale application of SMS in the field.