To impede nitrogen loss due to leaching and NH3 volatilization, pristine urea particles are coated with synthetic polymers such as poly(acrylic acid) and polyethylene for the controlled release of nitrogen. However, due to nonbiodegradability and environmental and economic issues, these synthetic polymers are replaced with cheap, biodegradable, and green coating materials. In this study, borax-modified starch biopolymer is used to produce controlled release urea (CRU) in a tumbling fluidized bed. Central composite rotatable design is used to study the interactive effect of process parameters on time and kinetics of nitrogen release. Nitrogen release in distilled water is monitored by the UV�Vis spectrophotometer and soil burial test is used to observe release in soil. The optimum values of process parameters and response objectives generated by the analysis of variance are validated by triplicates of confirmation runs and the error is reported as a precision indicator. A mathematical model is used to determine the diffusion coefficient of nitrogen release. Biopolymer-coated urea results in much better release performance when compared with starch-based CRU reported in the literature. The most influential process parameter both for time and kinetics of nitrogen release appears to be the coating time. Release time increases linearly with coating time and the diffusion coefficient decreases with increase in coating time. The kinetic study reveals that some of the samples followed non-Fickian diffusion and others followed Case-II transport during the release of nitrogen. © 2018, © 2018 Taylor & Francis.