Preparation of biodegradable sodium alginate/carboxymethylchitosan hydrogels for the slow-release of urea fertilizer and their antimicrobial activity

Nonpolluting and biodegradable hydrogels for the slow-release of urea fertilizer that also exhibit antimicrobial activity against some pathogenic bacteria and fungi in soil were developed. The sodium alginate/O-carboxymethyl chitosan hydrogels (Alg/O-CMCh) were prepared by blending the components in the presence of calcium chloride as a crosslinker. Some variables that affected the controlled loading and release of urea were investigated, including the polymer blend ratios of the components in the hydrogels and the concentration of the crosslinker. The prepared hydrogels were examined via Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, and their antimicrobial activity was also analyzed. The data show that the release of urea reached equilibrium after 26 days, with a cumulative percentage of approximately 75%–91%. The kinetics of urea release were fitted to zero-order, Higuchi, and Korsmeyer-Peppas models. Overall, the prepared hydrogels exhibit better antimicrobial activity than O-CMCh alone.