Modelling nutrient release from controlled release fertilisers

A new diffusion model is proposed that comprehensively simulates nutrient release from the coated fertiliser particles at all release stages. The model is universal, because it enables the nutrient release rate and pattern of the cumulative release curve to be predicted for all types of coatings provided that the release process follows a diffusion mechanism. The novelty of the model is that nutrient diffusion is not considered in the solid layer, but in the solution with which the coating layer is impregnated. The model considers that nutrient diffusive flux in the coating layer depends on the moisture content of the coating and the counter diffusive flux of moisture. The nutrient release in aqueous medium is described by two second-order partial differential equations and two first-order ordinary differential equations with corresponding initial and boundary conditions without dividing the process time into periods (lag, linear and decay ones). The proposed model requires determination of only three coefficients: water and nutrient diffusion coefficients in the coating layer, and the limiting water absorption value of the coating material. The adequacy of the model was verified using experimental data on the kinetics of urea release from polymer-coated urea. The model adequately describes experimental data obtained both by the article authors and by other researchers.(c) 2023 IAgrE. Published by Elsevier Ltd. All rights reserved.