Formaldehyde-crosslinked GIPANA–polyacrylamide hydrogel improves root-zone soil moisture, infiltration, and crop yield under arid irrigation in the Turkistan Region

This study evaluated a superabsorbent polymer (SAP) hydrogel synthesized from hydrolyzed polyacrylonitrile (GIPANA) and an anionic polyacrylamide component cross-linked with formaldehyde for improving soil water status and crop performance under arid field conditions in the Turkistan Region (Saryagash District, Kazakhstan) during the 2024 growing season. A randomized complete block design with three replicates tested three crops (rice, wheat, saffron) under three hydrogel treatments: control (T0), 0.2% (w/w) hydrogel (T1), and 0.4% (w/w) hydrogel (T2), with identical crop-specific irrigation inputs across treatments. Soil moisture was monitored using TDR at 0–10, 10–20, and 20–40 cm depths over time; field infiltration, wetting depth, and a retention coefficient were determined using double-ring infiltrometry; and laboratory swelling capacity was measured for unmodified and Ca–P modified hydrogels. The experimental soil remained non-saline and chemically stable across the season, enabling attribution of observed responses primarily to hydrogel amendment. Hydrogel application increased volumetric soil water content in a consistent dose-responsive manner across crops and depths, with the largest and most persistent gains under T2, particularly in the 20–40 cm layer in rice later in the season. In parallel, infiltration rate, wetting depth, and retention coefficient increased substantially with hydrogel dose. Laboratory tests confirmed rapid swelling and high absorption capacity, which further increased with Ca–P modification. Improved soil water availability translated into enhanced vegetative growth (plant height and leaf number) and higher yields in all crops, with T2 providing the most consistent agronomic benefits. Overall, the results demonstrate that GIPANA–polyacrylamide hydrogel amendment can improve root-zone moisture dynamics, soil water transmission, and crop productivity in arid irrigated systems, supporting its use within integrated water-saving soil management strategies.