A urea-loaded hydrogel comprising of cellulose nanofibers and carboxymethyl cellulose: An effective slow-release fertilizer

Conventional fertilizers used worldwide to increase crop yield have several environmental and economic issues resulting from their quickly soluble nature, causing most of the fertilizers to be lost through agricultural field runoff and leachate. Utilizing slow or controlled-release fertilizers may reduce the issues associated with conventional fertilizers. However, many commercially available variants of slow-release formulations are ecologically unsustainable as they are made of non-biodegradable polymers. In the present study, a hydrogel composed of cellulose nanofibers (CNF) and carboxyl methyl cellulose (CMC) was synthesized for use as a biodegradable and environmentally sustainable host for carrying urea within its matrix and released the same slowly over a long period of time. The swelling measurements showed that the thermally stable urea-loaded CNF/CMC hydrogel (UCNF) had a high water absorption capacity of 147 g/g in distilled water owing to its porous morphology and the presence of various polar groups. When exposed to a dry environment, it released the absorbed moisture slowly over a period of more than 2 weeks. The urea release rate was also relatively slow; it took about 30 days to release the urea loaded in UCNF. The results indicated that urea diffusion from the material was non-Fickian in character and fit well with the pseudo-second-order kinetics model. The hydrogel demonstrated excellent biodegradability; more than 80% by weight of the hydrogel disappeared through biodegradation by soil bacteria within 3 months. The plant study revealed that adding UCNF to the soil effectively enhanced the seed germination and growth of the plant. Also, plants treated with urea-loaded hydrogel had better growth than the pure urea- and control plant samples. The study found that crosslinked and functionalized cellulose nanofiber may effectively transport water and fertilizer slowly and sustainably.