Mathematical Model for Potassium Release from Polymer-coated Fertiliser

An exact mathematical model based on Fickʹs Second Diffusion Law was developed to predict the release rate of polymer-coated fertiliser using a numerical solution and Fourier series expansion. From the explicit mathematical model, an approximate solution for the nutrient release was obtained. The model showed that the nutrients release was mainly controlled by the diffusion coefficient, membrane thickness and granule radius. This model was simpler compared with the original numerical solution, and different radii of polymer-coated controlled-release fertiliser was used to verify the approximate release model. The nutrient was mainly released in the linear stage, and the cumulative percentage of nutrient release decreased when the granule radius increased. The cumulative release profile of potassium from the polymer-coated fertiliser into water agreed with the prediction of the model on the whole.