Carboxymethyl cellulose/urea hydrogel for seed pelleting: reversible water management at the seed-soil interface improves germination and drought-resilient establishment.

A carboxymethyl cellulose/urea (CMC/urea) hydrogel was developed via an EDC/NHS-mediated reaction as a water-managing component for seed pelleting under drought-prone conditions. FTIR, XPS, SEM and rheological analyses revealed a nitrogen-containing, porous and elastic CMC-based network with high water-storage capability. The optimized hydrogel exhibited equilibrium swelling and re-swelling capacities of 189.64 and 280.51 g·g-1, respectively, and retained approximately 91% of absorbed water after 7 days at 25 °C, demonstrating its capacity for prolonged and reusable water buffering. The hydrogel showed progressive mass loss during soil burial, with no visible fragments remaining by day 32. When integrated into an optimized seed-pelleting system, the CMC/urea hydrogel increased the germination percentage of Scutellaria baicalensis from 55.33% to 74.00% and outperformed a conventional sodium polyacrylate-based coating. The germination benefit extended to Glycyrrhiza uralensis and Astragalus membranaceus, indicating applicability beyond a single medicinal species. Under water-withholding stress, hydrogel pelleting delayed seedling wilting, limited H2O2 and malondialdehyde accumulation, maintained antioxidant enzyme activities, and moderated osmolyte accumulation. These results support a structure-property-function relationship linking the CMC/urea hydrogel network and its reversible water-management properties to improved seed-soil microenvironment and drought-resilient establishment, providing a cellulose-based alternative to synthetic superabsorbent seed coatings.