Abstract: Disclosed herein are superabsorbent hydrogels formed using okara particles and polymeric chains. The hydrogel contains crosslinks, which are provided by crosslinking groups between the polymeric chains or by a plurality of polymer chains being bonded to each okara particle (with each of these chains being bonded to at least one further okara particle too). The resulting superabsorbent hydrogels are useful in aiding plant growth, nutrition and hydration, and may be mixed with soil to form a composite material for such purposes.