Biodegradable Nanoclay–Agarose Hydrogels as Sustainable Substrates for Seed Germination

Abstract

Conventional seedling substrates such as rockwool and peat raise environmental concerns associated with disposal and resource extraction. Here, we investigate nanoclay–agarose hydrogels as candidate sustainable and biodegradable alternatives for seed germination and early plant growth under greenhouse conditions. Agarose hydrogels incorporating sodium bentonite nanoclay (NC) or activated carbon (AC) were prepared and evaluated for their structural, thermal, and biological performance using Brassica rapa (bok choy) as a model crop. Structural and physicochemical analyses revealed lamellar architectures, spectral features consistent with agarose–filler interactions, and composition-dependent thermal decomposition profiles. Dried NC hydrogels exhibited more open structures than the comparatively compact AC hydrogels. After 15 days under greenhouse conditions, NC40 (40 wt% nanoclay relative to agarose) achieved 100% germination and the highest mean fresh and dry biomass among the substrates compared for biomass, including rockwool and peat pellets. Over 42 days of soil burial, pure agarose and AC hydrogels showed more extensive visible breakdown consistent with biodegradation of the agarose matrix, whereas NC hydrogels retained their structural form for longer. These findings highlight nanoclay–agarose hydrogels as biodegradable, eco-engineered substrates with the potential to replace conventional growing media and advance sustainable agriculture.