Cassava starch‐graft‐poly(acrylonitrile)‐coated urea fertilizer with sustained release and water retention properties

Abstract Cassava starch‐graft‐poly(acrylonitrile) samples were synthesized by a free radical‐initiated polymerization reaction, and urea fertilizer was coated with these grafted starches to obtain the dual benefit of sustained release and water retention properties. A response surface design was used to optimize the synthetic conditions of starch‐graft‐copolymers to maximize the slow nutrient release and water absorbency. The FT ‐ IR analysis confirmed the grafting reaction, and scanning electron micrographs revealed the ultrastructure of polymer coating. The release of nitrogen in soil from coated urea was more sustained than that from uncoated urea and it varied with grafting level of the polymer. The uncoated urea showed almost complete release of nitrogen by 1 month, whereas %N release was in the range of 69.8%–78.3% from the grafted starch‐coated urea even after 108 days of incubation. The water retention capacity of the coated urea ranged from 74.2% to 426.6% and it decreased with increase in % grafting of the coating material.