A field study on using soybean waste-derived superabsorbent hydrogel to enhance growth of vegetables

Food security is critical and has become a global concern with many of our basic food crops growing in areas with high drought risk. To improve soil water holding capacity, hydrogels are a promising solution. However, the current ones are mostly derived from petroleum products and are environmental unsustainable. In this study, the main objective is to determine if bio-based hydrogel can help in the growth of leafy vegetables while minimizing water use under field conditions. To achieve this, we developed an okara-derived hydrogel (Ok-PAA; OP) from by-products of bean curd and soybean milk production. We incorporated OP into soil and assessed the growth performance of leafy vegetables. We observed that vegetables grown with 0.2% (w/v) OP in soil with a watering frequency of 7 times per week resulted in >60 % and 35 % yield increase for the common Asian leafy vegetables, choy sum (CS) and pak choi (PC), respectively, as compared to without hydrogel supplementation. Both vegetables produced larger leaf areas (20-40 % increment) in the presence of the hydrogel as compared to those without. In addition, with OP amendment, the irrigation water use efficiency improved >60 % and 30 % for CS and PC, respectively. It is estimated that with the use of the hydrogel, a reduction in watering frequency from 21 times to 7 times per week could be achieved, and based on a per hectare estimation, this would result in 196,000 L of water saving per crop cycle. Statistical analysis and modelling further confirmed vegetables grown with 0.2 % (w/v) OP and with a watering frequency of 7 times per week showed the best growth performance and water use efficiency. Such a waste-to-resource approach offers a plant-based soil supplement for crop growers, contributes to waste valorization, and enhances the growth of plants especially under water-limited conditions.