Controlled Release of Urea from Rosin-Coated Fertilizer Particles

A mathematical model describing the controlled release of urea from rosin-coated urea granules has been developed on the basis of the experimental results. The release mechanism was also elucidated from the experimental observation on the release from a single pellet. Two classes of release pattern were observed from single-pellet release experiments including (1) immediate and relatively rapid release through a few holes or many microscopic pores originally present in the coating and (2) little or no release for an extended period of time followed by a sudden, rapid release through the holes formed in the coating. It was found that individual granules could not give sustained release of urea by itself. Applying the mathematical model developed for a single pellet to real systems in which coating weight distribution is present, we obtained good agreements between model predictions and experimental results.