Biobased alginate/cellulose composite hydrogel as a seed microenvironment chamber for water retention and controlled nutrient delivery

Seed germination and early seedling establishment are often constrained by insufficient water availability and inefficient nutrient utilization, particularly under water-limited conditions. To address this, a biobased SA/C-Gel composite hydrogel loaded with fertilizer was developed as a seed microenvironment chamber, integrating sodium alginate (SA) with a cellulose-derived gel (C-Gel) to achieve synergistic water retention and controlled NPK release in close proximity to the seed growing. Structural characterizations confirmed that SA and C-Gel formed a stable, interconnected three-dimensional porous network, whose architecture could be precisely tuned by adjusting the C-Gel ratio. The optimized hydrogel exhibited dramatically enhanced swelling (∼19,000 wt%, ∼10-fold higher than pristine SA) and prolonged water retention (14-18 h at 30 °C), while NPK loading enabled sustained nutrient release in both aqueous and soil environments, following a Fickian diffusion mechanism. Soil burial experiments demonstrated controlled biodegradation (42-66% over 12 weeks) and enhanced soil microbial activity, confirming environmental compatibility. Seed germination assays using Elymus dahuricus showed significantly improved germination rates, stem elongation, and root development, particularly for the SA/C-Gel-30/NPK formulation. By integrating water and nutrient regulation within a confined hydrogel matrix, this system establishes a self-sustained microenvironment that promotes early-stage plant growth. This study proposes a scalable and sustainable strategy, demonstrating the feasibility and potential of converting biopolymers into multifunctional seed coating materials, as a practical and promising solution to conventional fertilizers and water-retention materials.