Preparation and properties of chitosan-coated NPK compound fertilizer with controlled-release and water-retention

To improve the utilization of fertilizer and water resource at the same time, a new type chitosan-coated nitrogen, phosphorus and potassium compound fertilizer with controlled-release and water-retention (CFCW) was prepared, which possessed the three-layer structure. Its core was water-soluble nitrogen, phosphorus and potassium (NPK) fertilizer granular, the inner coating was chitosan (CTS), and the outer coating was poly(acrylic acid-co-acrylamide) (P(AA-co-AM)) superabsorbent polymer. Atomic absorption spectrophotometer and element analysis results showed that the product contained 7.98% potassium (shown by K2O), 8.14% phosphorus (shown by P2O5), and 8.06% nitrogen. The synthesis conditions of inversion suspension polymerization were studied systematically. The water absorbency of the product was 70 times its own weight if it was allowed to swell in tap water at room temperature for 90 min. The nutrients slow release behaviors of the CFCW in soil and water-retention capacity of the soil with CFCW were investigated. A possible slow release mechanism was proposed and the release rate factor K and the release exponent n of nutrients in CFCW was calculated. This product with good controlled-release and water-retention capacity, being degradable in soil and environment-friendly, could be especially useful in agricultural and horticultural applications.