Phosphorus fertilizer coated with polysaccharide-enriched extracts from the red seaweed Schizymenia dubyi for slow release and water retention

The present study investigates the feasibility of using polysaccharide enriched extracts (PEEs) from the red seaweed Schizymenia dubyi as coating materials in the preparation of controlled release triple superphosphate (TSP) fertilizers. Initially, the polysaccharide was isolated, extracted, and further characterized by gas chromatography and infrared analysis to determine its chemical composition and its partial structure. Results of chemical and spectroscopic analysis indicated that galactose, glucuronic acid, and glucose were the main components of the polysaccharide with a molecular weight of 2805 KDa. It can be suggested that this polysaccharide could be a sulfated glucuronogalactan. After that, the viscosity of the coating polysaccharide solution at different concentrations was conducted to determine the low and high polysaccharide concentrations that can be easily sprayed. After the spray coating process using different concentrations (1.8% and 2.5% w/v) and application cycles (from C1 to C4), the resulting coated fertilizer beads were chiefly characterized in terms of morphology, release kinetics in water and soil, and water retention properties. Results of the phosphorus release kinetics in water showed an effective effect for the slow release behaviour of the fertilizer. Increasing the concentration of the matrix additionally delays the release of P, and the best results were obtained with the formulation 2.5% -C4 which released 75% P after 5 to 7 days versus 2 days for the uncoated TSP. The same tendency was also recorded in soil release kinetics and weight losses. The soil water retention was also improved with the coated fertilizers, with over 4% more water retention than the uncoated fertilizers over 28 days. These findings showed that the polysaccharide-coated TSP fertilizer had multiple agronomic features and could be a promising candidate for various potential applications in agriculture.