Controlled release fertilizer (CRF) is a prominent green technology that helps to reduce the adverse effect of fertilizer on the environment. A good CRF is expected to synchronize with the nutrient uptake of plants along the crop duration. The water absorption which related to the delay of nutrient release also plays an important role in order to produce a good CRF. This work studied the water absorption in the coating and in the fertilizers using weighing technique. Moreover, the relationships between the absorption processes with the release of nutrient were also pointed out and compared to those in literature. Results showed that water penetration in the coating took place sooner and faster than that in the fertilizers. And, the lag time in nutrient release profile should be linked to the water infiltration in the coating rather than that in fertilizers. Moreover, the absorbency curve followed a first-order kinetic and was similar to cited literature

Pristine urea is lost due to ammonia volatilization and leaching causing toxic emissions and eutrophication. Controlled-release urea is employed as an abatement strategy. Most of the synthetic polymers used to produce controlled-release urea are non-biodegradable and expensive. To offset this problem, modified-starch biopolymer is used as coating material to produce controlled-release urea in fluidized bed. The effect of different process variables is studied on release characteristics and coating uniformity of coated urea. The product has better release characteristics. The statistical analysis reveals that fluidizing gas temperature and coating time are the most influential variables. The nutrient release time increases with increase in coating time and decreases with increase in fluidizing gas temperature beyond a certain limit. Coating uniformity, significant thickness and film integrity are required for promising release characteristics. Urea release followed non-Fickian diffusion and Case-II transport. This study can help produce green fertilizer at bigger scale.