Controlled-Release Fertilizer Based on Chitosan Hydrogel: Phosphorus Release Kinetics

This paper describes the phosphorus release behavior of controlled-release fertilizer (CRF) hydrogels,which were prepared from polyvinyl alcohol (PVA), chitosan (CS) and the blend of these twopolymers, using glutaraldehyde as a crosslinker. The mechanisms of phosphorus release from the CRFhydrogels were investigated using the Korsmeyer-Peppas model. It was found that, both in deionizedwater and in soil, the values of n for all the CRF hydrogels are smaller than 0.5, indicating that thereleases of nutrients from CRF hydrogels are a quasi-Fickian diffusion mechanism. Swelling ratio andwater retention in soil of CRF hydrogels were investigated. The PVA hydrogel showed the highestvalue of equilibrium water absorbency and water retention among all the synthesized hydrogels. Thisis due to PVA is more hydrophilic than CS. The chemical structure, therefore, was important factorsthat affected the swelling ratio of the hydrogels which is directly related to the release rate ofphosphorus from the CRF hydrogels.