Urea Controlled-Release Fertilizer Based on Gelatin Microspheres

Gelatin microsphere, as a sustained release urea carrier, was prepared by an emulsion-cross linking method with glutaraldehyde (GA) as a cross-linking agent. The influence of urea/gelatin ratio, emulsifier, GA concentration, and cross-linking time on the urea loading and encapsulation efficiency was investigated using response surface methodology. It was found that the urea/gelatin ratio had greater impact on urea loading and encapsulation efficiency than other factors. Equilibrium swelling of microspheres were performed in distilled water, and as expected, the water uptake decreased with the increase of GA as well as the reaction time. The cumulative release of urea from the microspheres decreased with the increase of reaction time and urea release presented a Fickian trend, indicating a diffusion controlled urea release mechanism. The insight from this study is useful to the design and process of controlled release urea fertilizers. [GRAPHICS] .