Polymer Hydrogel–Humic Compositions for Retaining Moisture in Sulphate-Crusted Rainfed Desert Soils of The Navoi Region At 30–50 °C

Rainfed desert rangelands of the Navoi region (Uzbekistan) receive less than 100 mm of precipitation a year, and spring rain moisture evaporates before the ephemeral vegetation sets seed. Soils of the Karmana, Navbahor and Konimex districts were characterised by X-ray diffraction, and moisture retention by locally produced polyacrylamide gel (PAM), sodium carboxymethylcellulose (CMC), humic substances from Angren brown coal (HS) and their compositions was measured gravimetrically at 30–50 °C. Salt minerals accumulated in the 0.2–0.5 cm surface crust and were of the sulphate type (22.5–39.5 wt.% sulphate minerals, mainly thenardite and astrakhanite; chlorides 0.4–0.8 wt.%). A comparison of a wet (2016) and a dry (2021) year identified April–May as the critical period of moisture deficit. The optimal concentrations were 3 g/L for PAM and 2 g/L for CMC. When untreated soil reached its minimum moisture (0.92–1.20 %), the compositions CMC 2 g/L + HS 3 g/L and PAM 3 g/L + HS 3 g/L still held 3.0–4.7 %, and their first-order drying constants were 1.5–3.1 times lower than that of the control. The combined effect of hydrogel and HS was not consistently synergistic (additivity index 67–227 %).

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