A rigid-flexible locust bean gum/acrylic acid hydrogel resists soil confinement for enhanced water retention

Water scarcity imposes a major constraint on agricultural systems, posing a direct threat to global food security and ecological balance. Superabsorbent hydrogels can significantly improve soil water holding capacity, thereby enabling the soil to effectively resist drought and sustain normal crop growth. However, the physical stress environment in soil severely compromises the water absorption and swelling capacity, limiting their agricultural application. To address this challenge, a locust bean gum/acrylic acid hydrogel (LAN) that combines a rigid sodium acrylate covalent network with a flexible, dynamic locust bean gum hydrogen-bonding network was prepared to improve the utilization of agricultural water resources. This design enables LAN to maintain a high swelling capacity under mechanical confinement. Specifically, LAN exhibits a swelling index of 362.64 g/g in deionized water. Crucially, under a simulated soil confining pressure of 0.36 kPa, the addition of 0.5 wt% LAN enabled sandy soil to retain a water content of 80.6%, extending the retention period from 6 to 22 days. The swelling mechanism under confined conditions is quantitatively explained by the balance between the internal swelling pressure and external soil stress. This work provides a viable strategy for developing hydrogels that perform reliably under real soil conditions.