Polyvinyl alcohol-soy protein isolate hydrogels: Controlled release of fertilizer and matrix nutrients for sustainable agriculture

Controlled release of fertilizers using hydrogels is one of the sustainable methods for increasing the effectiveness of chemical fertilizers and reducing their adverse effects on the environment. Here, we report an eco-friendly hydrogel based on polyvinyl alcohol (PVA) and soy-protein isolate (SPI) crosslinked with citric acid (CA) for the controlled release of fertilizer. Initially, PVA-SPI blends (PS) were prepared by solvent casting method and studied their physiochemical properties. The optimized blend (PS 8/2) was crosslinked with various weight percentages (5–30%) of citric acid (CA). Hydrogels with 20% CA exhibited optimum properties which were then loaded with urea to prepare controlled release fertilizer hydrogel (CRFH). Spectrophotometry studies showed that 74.1% of urea was released by the samples in 28 days. Additionally, the soy-protein matrix released the nutrients along with urea, which can be considered an added benefit. Kinetics study revealed that the release of nutrients followed the Ritger-Peppas model. The water retention study indicated that the samples could retain water for up to 30 days with an increase in gel content. Plant growth performance, germination and drought resistance study were evaluated using amaranthus and pea seedlings as model plants. The results indicated a significant improvement in the growth performance of the plants. Also, a degradation rate of 65% was attained for hydrogel samples when it was buried in the soil for 100 days. The prepared hydrogels can therefore be regarded as a potential candidate for sustainable agriculture due to their controlled-dual release properties, water-retaining capacity, affordability, non-toxicity, and environmental friendliness.