Urea-rubber matrices as slow-release fertilizers

The effect of temperature and fertilizer particle size on urea release from a novel urea-rubber matrix (URM) composite was studied by incubation in 0.01 M CaCl2 solution. The release rate of urea from URM increased with increasing temperature and decreasing URM cuboid size which was well predicted by a diffusion-based model. However, the value of tortuosity factor, used in the model description, increased with increasing temperature. This may represent a genuine effect, due to changes in the morphology of the rubber pore walls, or may arise from deficiencies in the simulation model. Simulations of urea release from URM cuboids, given the predictable effects of both temperature and cuboid size, showed potential applications in a wide range of agricultural systems. As presented, the model is only strictly applicable to situations in which soil moisture is not limiting, such as paddy soils.