Parametric evaluation using mechanistic model for release rate of phosphate ions from chitosan-coated phosphorus fertiliser pellets

• Phosphate release rate through chitosan-coated fertilizer pellets were extensively studied.
• The effect of number of coatings and pH conditions to the release rate were examined.
• The mathematical model to evaluate the respective parameters was developed.
• The release rate increases as the number of coatings and pH values being decreased.
• Experimental data were found to fit the model.

Evaluation of nutrient release from a controlled-release fertiliser (CRF) using mechanistic model is important in order to increase the understanding towards the mechanism that might involve in a release process. In this study, a mechanistic model was used to evaluate the parameters that govern the phosphate release rate through chitosan-coated phosphorus fertiliser. The model considers the phenomena of boundary layer formation on the external surface of the coat and the coating thickness changes due to erosion. Static release experiments were conducted in order to study the effect of the number of coatings and pH conditions to the release rate of phosphate ions. The respective parameters of the phosphate release such as diffusion coefficient were evaluated using the model in both cases. The diffusivity of the phosphate was found to increase as the number of coatings and pH values of the medium decreased. Regeneration of the released data for the phosphate ions using the model indicated a very satisfactory fit with the experimental data.