Seaweed Based Hydrogels: Extraction, Gelling Characteristics, and Applications in the Agriculture Sector

Due to expanding seaweed-based industries and thegrowing popularity of seaweed biorefineries, there is an increasingopportunity for high-value applications of seaweed-extractedpolysaccharides. One of the most fascinating applications forthese biopolymers is in the field of agriculture, where they havebeen used as fertilizers, hydrogel/granules for slow release of urea,herbicides, insecticides, and water reservoirs to tackle drought-likesituations. Polysaccharides, such as alginate, agar/agarose, ulvan,carrageenan, etc., have been used as such for a long time inmultiple applications; however, their use in the development ofhydrogels and subsequent utilization to deal with agriculturalchallenges like drought mitigation, to reduce chemicals leachingfrom fertilizers, or to lessen the harmful impacts of pesticides andincrease crop yields, has recently gained a significant amount of interest from scientists. In this review article, we thoroughly discussthe technique generally utilized to extract polysaccharides from seaweeds, the structure, the gelation mechanism, and agriculturalapplications of various hydrogels, namely, alginate, agar/agarose, ulvan, and carrageenan. The impact of various bioadditives andsurface modification techniques on the properties of polysaccharide-based hydrogels, such as water absorption/retention tendency,variation in fertilizers/pesticide releasing capability, etc., are discussed. Finally, the challenges along with some future possibilities arealso discussed.