Protein-Rich Supplements Improved the Agronomic and Nutritional Quality of Stropharia rugosoannulata

Stropharia rugosoannulata is efficiently cultivated using agricultural and forestry wastes, such as sawdust and straw, and has gained popularity in China for its rich nutrition and excellent taste. However, traditional cultivation methods, which lack nitrogen supplementation, often result in low yields and poor fruiting body quality. This study evaluated the effects of protein-rich supplements (PRSs)—feather meal (FM), soybean meal (SM), and their mixture (FS)—on substrate properties, yield, and nutritional quality. PRS significantly increased substrate total nitrogen (TN), reduced the C/N ratio, and improved fruiting body yield, with FM achieving the highest yield (6.80 kg·m−2). Moreover, FM and FS significantly enhanced the contents of crude fat, crude fiber, crude protein, crude polysaccharides, total amino acids (TAAs), essential amino acids (EAAs), and umami amino acids (p < 0.05). Additionally, FS significantly enhanced antioxidant activity and 1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity of crude polysaccharides (p < 0.05). These findings demonstrate the potential of PRS to optimize S. rugosoannulata cultivation, offering a cost-effective strategy to improve commercial production.