Superabsorbent Hydrogels Derived from Okara as Soil Supplements for Enhancing Vegetable Growth and Production

Okara (Ok), a byproduct of the soybean milk and soybean curd industries, is primarily disposed of or incinerated as waste. However, given that Ok is a naturally renewable bioresource, it is crucial to explore potential applications for converting Ok into valuable materials. In this chapter, we present approaches involving the chemical modification of Ok through free radical graft copolymerization, and the conversion of Ok into superabsorbent hydrogels via copolymerization with acrylic acid (AA) and acrylamide (AAm). The synthesis strategies for Ok-PAA graft copolymers, Ok-P(AA-AAm) and Ok-PAA superabsorbent hydrogels are extensively discussed. Various characterization techniques for the Ok-derived hydrogels are reviewed, including analyses of the molecular structure, morphology, swelling behavior, water holding capacity, and water retention capacity. Additionally, we discuss the application of these Ok-based hydrogels as soil supplements to enhance vegetable growth and production. The utilization of these hydrogels presents a remarkable opportunity to promote plant survival, improve water use efficiency, and reduce watering frequency in both laboratory and field conditions. The utilization of Ok-derived hydrogels as a plant-based soil supplement enhances plant growth in water-limited conditions, contributes to waste valorization, and offers potential for sustainable and effective agricultural practices.