Release Kinetic Models and Release Mechanisms of Controlled-Release and Slow-Release Fertilizers

The theory of slow release and controlled release has the versatility of applications in pharmaceuticals, fertilizers, and agrochemicals. In controlled-release and slow-release administration, inorganic and organic materials and polymers that are both degradable and nondegradable have numerous uses. Research on release kinetics reveals how material systems work. Release kinetics can be determined using statistical methods, model-based methods (curve fitting techniques), and model-independent techniques. Curve-fitting techniques have been applied to describe drug-releasing behaviors in pharmaceuticals. This review describes curve-fitting methods used by researchers to analyze the nutrient release profile using different models, such as zero-order, first-order, Higuchi, Korsmeyer–Peppas, Hixson–Crowell root law, Ritger–Peppas, Peppas–Sahlin, and Weibull models. These drug-release models have successfully explained the release behavior of controlled-release and slow-release fertilizers and agrochemicals. Fertilizer type, rate of application, application time frame, and application location are all crucial factors in nutrient management. The known transport and release mechanisms support increasing profitability and adhere to nutrient best management practices. Hence, in this study, we will review existing controlled- and slow-release fertilizer systems in detail that are explained using the aforementioned modeling approaches (empirical and mechanistic) to discuss recent developments and applications of controlled- and slow-release fertilizer systems.