Polysaccharide Hydrogels for Controlling the Nutrient Release

Nutrient run-off from agriculture causes water pollution and eutrophication. Polysaccharide hydrogels with controlled release of nutrients have been developed to minimize nutrient leaching and run-off. This review compares the loading and release of different nutrients from polysaccharide hydrogels for fertilizing purposes. Urea was encapsulated into polysaccharide hydrogels through blending, adsorption, and coating to minimize fast hydrolysis and possible volatilization. Urea release could be controlled by incorporating inorganic fillers, increasing polymer density, and reducing pore size. Early works incorporated polysaccharides into synthetic polymer hydrogel. Cellulose, cellulose derivatives, starch, chitosan, and alginate were later used as the composite hydrogel in urea encapsulation. The controlled release of other nitrogen sources such as KNO3, NH4NO3, NH4Cl, and leather waste was also studied. Phosphate release was reduced using copolymers containing Arabic gum, carboxymethyl cellulose, and starch-rich waste besides chitosan and carboxymethyl cellulose hydrogels. Potassium release from polysaccharide hydrogel containing nitrogen, phosphorus, and potassium could be electrostatically controlled. Polysaccharide hydrogels containing micronutrients, humic acids, and sucrose were also developed. Most of the polysaccharide hydrogels did not fulfill the nutrient release standards. Besides controlling the release of multiple nutrients, further reduction of cost using polysaccharide-rich waste and nutrients in the wastewater should be considered.