Combined Application of Myo-Inositol and Corn Steep Liquor from Agricultural Waste Alleviate Salt Stress in <i>Brassica rapa</i>

Salinity poses a significant threat to plant growth through induction of osmotic and ionic stress and disruption of nutrient absorption. Biostimulants derived from agricultural waste offer a sustainable solution to alleviate salt-induced damage to plants and contribute to a circular and sustainable economy. In this study, we applied a combination of myo-inositol and corn steep liquor from waste sources to seedling cabbage (<i>Brassica rapa</i> subsp. <i>pekinensis</i>) and investigated their effects on plant growth under NaCl-simulated salt stress. Different concentrations of myo-inositol and corn steep liquor were applied to the roots, revealing that 150 mM NaCl significantly inhibited the growth and physiological metabolism of cabbage seedlings. Substrate application of myo-inositol, corn steep liquor, and their combination materials increased biomass, photosynthetic pigments, soluble sugars, soluble proteins, and the contents of K⁺, Ca²⁺, and Mg²⁺ in cabbage under salt stress conditions, while reducing malondialdehyde, electrolyte leakage, Na+ content, and the ratios of Na⁺/K⁺, Na⁺/Ca²⁺, and Na⁺/Mg²⁺. Therefore, root application of myo-inositol, corn steep liquor, and myo-inositol–corn steep liquor combination materials enhanced photosynthesis and enhanced cabbage salt stress resistance by maintaining cell osmotic and ion balance. The most pronounced positive effects were observed in the treatment with 0.1 mL L⁻¹ corn steep liquor +288 mg L⁻¹ myo-inositol. This study provides a theoretical basis and technical guidance for the combined utilization of myo-inositol and corn steep liquor to boost early growth and salt resistance in crops.