Localized subsurface placement of a polyacrylamide superabsorbent polymer improves soil moisture distribution and reduces irrigation requirement in wheat grown in Eastern Kazakhstan

Water scarcity and increased drought frequency threaten irrigated cereal production across arid and semi-arid regions. Superabsorbent polymers (SAPs) can improve soil water retention and reduce non-productive losses, but field-scale effectiveness depends strongly on placement strategy and soil conditions [1–5]. This study evaluated a commercially available cross-linked polyacrylamide SAP applied locally using a slitter-based implement at two rates (30 and 60 kg ha⁻¹) and two placement depths (20 and 40 cm) under irrigated wheat (Triticum aestivum L., cultivar ‘Steklovidnaya-24’) in Eastern Kazakhstan (April–June 2025). A randomized complete block design with three replications was used (6 × 4 m plots). Soil moisture was measured by depth (0–5, 0–20, 20–40 cm) using the thermostat–weight (oven-drying) method; soil reaction (pH) was measured in a salt extract prepared by the TSINAO method using a calibrated pH meter; and grain yield was assessed by whole-plot harvest and converted to a hectare basis. Localized SAP placement redistributed water downward, with a 3.6–3.8 percentage-point reduction in the 0–20 cm layer and a 3.2–3.6 percentage-point increase in the 20–40 cm layer, resulting in an 8–11% increase in root-zone moisture reserves. The number of irrigations decreased from two to one, reducing seasonal irrigation from 1,800 to 900 m³ ha⁻¹, while crop growth indicators visibly improved relative to the control. Overall, 30 kg ha⁻¹ placed at 20 cm provided the most favorable balance between agronomic benefit and input intensity, consistent with broader evidence that targeted subsurface SAP placement can enhance irrigation water productivity.