Influence of super absorbent hydrophilic polymers on enhancing resources use efficiency and crop productivity in Vertisols

Water scarcity is a significant challenge in agriculture, particularly in arid and semiarid regions. Superabsorbent polymers (SAPs), such as hydrogels, have emerged as effective tools for enhancing soil moisture retention and improving crop yield and water productivity in these environments. A two-year field study was conducted to examine the impacts of hydrogel type and application depth on soil water distribution, water productivity and spinach growth. Two types of hydrogels, polymer-based (Hydrogel-1) and small organic molecule-based (Hydrogel-2), were applied at three depths—surface (D₁), 5 cm (D₂) and 10 cm (D₃)—in a randomized block design. The results revealed that the water absorption capacity and water salinity of Hydrogel-1 were negatively correlated, whereas those of Hydrogel-2 were unaffected by salinity. Compared with that of the control, the soil moisture retention improved with deeper hydrogel application, with the Hydrogel-1 treatment at 10 cm extending irrigation intervals by 2–4 days. Hydrogel application at greater depths significantly increased spinach growth metrics, including plant height, leaf count, leaf area, root length, SPAD value and yield, resulting in the highest yield (5.7 kg/m²) and water productivity (44.8 kg/m³). The study concludes that applying hydrogels at a depth of 10 cm is optimal for maximizing resource use efficiency and water productivity in spinach grown in vertisols.