Copyright  2010 Faculty of Science, Ubon Ratchathani University. All Rights Reserved. SCIENCE JOURNAL Ubonratchathani University http://scjubu.sci.ubu.ac.th *Corresponding author. E-mail address: kaewpiro@buu.ac.th Sci. J. UBU, Vol. 1, No. 1 (January-June, 2010) 43-50 Controlled-Release Fertilizer Based on Chitosan Hydrogel: Phosphorus Release Kinetics T. Jamnongkan 1 , S. Kaewpirom 2 * 1 Department of Chemistry and the Center of Excellence for Innovation in Chemistry, Faculty of Science, Burapha University, Chonburi 20131, Thailand. 2 Department of Chemistry and the Center of Excellence for Innovation in Chemistry, Faculty of Science, Burapha University, Chonburi 20131, Thailand. Received 21/12/09; Accepted 26/05/10 1. Introduction In agriculture, loss of nutrient elements is one of large problems. It causes the insufficient of plant nutrients, increases process cost and pollutes the environment. Controlled release is a method used to solve this problem. With the use of controlled-released systems, nutrie- nts are released at a slower rate throughout the season, plants are able to take up most of the nutrients without waste by leaching [1-2]. Polymer hydrogels can be defined as three-dimensional polymeric networks that can retain a significant amount of water within their structures, and swell without dissolving in water [3]. Polymer hydrogels have been used for agricultural as controlled release fertilizer [4]. In the recent years, research on slow and controlled-release fertilizer has been mainly focused on regul- ating nutrients-release rate and on coating slow and controlled release fertilizers. Abstract 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 two polymers, using glutaraldehyde as a crosslinker. The mechanisms of phosphorus release from the CRF hydrogels were investigated using the Korsmeyer-Peppas model. It was found that, both in deionized water and in soil, the values of n for all the CRF hydrogels are smaller than 0.5, indicating that the releases of nutrients from CRF hydrogels are a quasi-Fickian diffusion mechanism. Swelling ratio and water retention in soil of CRF hydrogels were investigated. The PVA hydrogel showed the highest value of equilibrium water absorbency and water retention among all the synthesized hydrogels. This is due to PVA is more hydrophilic than CS. The chemical structure, therefore, was important factors that affected the swelling ratio of the hydrogels which is directly related to the release rate of phosphorus from the CRF hydrogels. Keywords: Controlled release, Hydrogel, Diffusion, Chitosan, Polyvinyl alcohol.