Synthesis of carboxymethyl cellulose-based superabsorbent hydrogel-biochar composite as an eco-friendly water retention agent for soil moisture management.

Conventional agricultural water retention agents (WRAs) are predominantly synthetic polymers, most commonly potassium polyacrylate, which improve water efficiency. However, they are poorly biodegradable and pose environmental concerns. Although natural polymers have been extensively studied for use in WRAs, fully biopolymer hydrogels typically exhibit water absorption capacity (WAC) below 500 g/g. By optimizing the ratios of carboxymethyl cellulose (CMC), epichlorohydrin (ECH), NaOH, and rice husk biochar, we have for the first time fabricated a superabsorbent fully biopolymer-based hydrogel-biochar composite (CMC-H-B) with a WAC of 3240.07 g/g. The swelling behavior under varying pH and salinity, performance in soils of three different textures, biodegradability, and effects on mung bean seed growth were evaluated for CMC-H-B to assess its preliminary applicability, with CMC-H (without biochar) and a commercial WRA (potassium polyacrylate) included for comparison. The results showed that CMC-H-B significantly improved soil water holding and retention capacities, matching the performance of potassium polyacrylate, while exhibiting superior biodegradability and minimal inhibition of mung bean early growth at a 1 % (w/w) application rate. These results highlight CMC-H-B's potential as an eco-friendly WRA for coarse soils in arid regions.