Sodium Lignin Sulfonate-Based Hydrogel Coatings for Slow Phosphorus Release and Enhanced Wheat Performance

To promote sustainable agriculture practices, a lignin-based hydrogel coating for phosphorus (P) fertilizers was investigated as a strategy to enhance P-use efficiency while mitigating its environmental and economic impacts. This study explores the effect of coated P fertilizers based on sodium lignosulfonate (L), chitosan (C), and polyvinyl alcohol (P v ) at varying concentrations. Compared to uncoated triple superphosphate (Uc-TSP), the coated fertilizers reduced P release by 33–53%, and improved water retention up to 8% after 27 days, whereas the control soil retained little water. After 60 days of cultivation, physiological responses improved significantly, including a two-fold increase in chlorophyll content, a 54% increase in leaf area, and a 23% increase in shoot dry weight. Additionally, total root P content increased by 70% and available soil P by 55% compared to Uc-TSP. Moderate lignin concentrations (CPL12 and CPL25) provided a favorable balance across all parameters. However, the highest lignin concentration (CPL50) resulted in the slowest nutrient release but reduced water retention, degradability, and plant growth performance. Statistical correlation analysis further supported these findings. Coating degradability exhibited a strong positive correlation with total dry biomass (r = 0.728), whereas high lignin levels were negatively associated with total P content. Overall, these findings showed that moderate lignin incorporation improved nutrient availability and plant growth, highlighting the potential of lignin-based coatings to enhance fertilizer efficiency in sustainable crop systems.