Characteristics of potassium release from polymer-coated controlled-release fertilizer and its modeling

Two kinds of polymer-coated controlled-release fertilizers(Multicoate) were used to study the characteristics of potassium release in the medium of water or water-saturated silicon sand in the column. The results show that the potassium release is mainly influenced by temperature and granule radius and shape. There is no significant difference in the potassium release rate in the medium of water and water-saturated silicon sand. Based on a theoretic model of nutrients release from polymer-coated controlled-release fertilizer, the factors that influenced the nutrients release in the water were studied, and sensitivity analysis was carried out. Temperature, fertilizer granule radius and membrane thickness influence the nutrients release significantly. The experimental value is significantly related with modeling one. However, the modeling value is significantly lower which is due to two factors: one is the granule shape that is not exactly spherical, the surface area(diffusion area) of granule used in the experiment is larger than modeling one. The other factor is the granule thickness which is not completely uniform and nutrients can easily release from the thinner part. Though there is a certain difference between experimental value and modeling value, the model is still very useful with great potential in the development of application in the polymer-coated controlled-release fertilizers.