Developing slow release fertilizer through in-situ radiation-synthesis of urea-embedded starch-based hydrogels

Slow release fertilizers based on starch-based hydrogels have attracted much attention because they are biodegradable, cheap and can retain soil water. It hypothesizes that in-situ radiation-synthesis can provide various unique advantages including eco-friendly, higher efficiency and homogeneously loading urea. This work introduced a novel method for developing slow-release fertilizers by in-situ radiation-synthesizing monolithic urea-embedded starch-based hydrogels through grafting polyacrylamide (AM). The effects of irradiation intensity on the hydrogels with various AM/starch ratios, concentrations and urea loading were studied. The structures and performances of the gel were investigated by FTIR NMR, SEM, and Rheometer. The urea fertilizer release rate strongly depends on the structures and strength of the hydrogel. The relationships between the gel structures and properties, and release rate were investigated and established. The results of FTIR and NMR show that starch grafted polyacrylamide was successfully synthesized by in-situ radiation. The results show that the radiation intensity and concentration increased the grafting and monomer conversion rates, but there was a maximum peak point for AM/starch ratio due to the self-polymerization of AM monomers. The gel strength increased with increased radiation intensity, AM content,and concentration, which led to the reduction of the urea release rate. The morphologies of the starch hydrogel changed from cottony to porous after adding urea. The monolithic urea-embedded starch-based hydrogels synthesized by radiation showed a promising potential to be new slow-release fertilizers fabricated by the eco-friendly, simple, and efficient method.