Ecofriendly renewable hydrogels based on whey protein and for slow release of fertilizers and soil conditioning

Abstract

Hydrogels show potential in agriculture for overcoming issues associated with conventional fertilizers and irrigation. A combination of hydrogels and fertilizers would limit the loss of fertilizer and curb environmental impact, especially for nitrogen-based compounds, in addition to diminishing the frequency of irrigation. A set of renewable hydrogels, based on a mixture of whey proteins and alginic acid were developed as a soil conditioner and for sustained release of the urea fertilizer. Four separate formulations were prepared from different proteins at a polysaccharide ratio of 1%–10% w/w (with respect to protein content). The hydrogels were prepared by a heat-set process, applying calcium chloride as the cross-linking agent. The fertilizer was loaded into the hydrogel during the preparation stage to heighten loading efficiency. Investigation was made into the impact of alginic acid content on morphology, swelling behaviour - encompassing repeated swelling-drying cycles, and water retention in soil under different pH conditions. The loading capacity and release of urea from the hydrogels were studied, and the data processed in accordance with a mathematical model to discern any correlation between the structure of the hydrogel, the presence of alginic acid and the release mechanism. The results demonstrate how adding alginic acid promotes possible utilization of the whey protein hydrogel in agriculture. © 2020 Elsevier Ltd