Kappaphycus alvarezii-Based Bioinputs for Sustainable Agriculture: Advances in Biofertilizers, Biostimulants and Controlled-Release Technologies

The red macroalga Kappaphycus alvarezii, widely cultivated for carrageenan extraction, has emerged as a promising blue economy resource of bioactive compounds for sustainable agriculture. However, knowledge regarding the composition, mechanisms of action, agronomic effects, and large-scale applicability of K. alvarezii-based products remains fragmented. Therefore, this review provides an overview of the potential of K. alvarezii and its by-products for the development of agricultural bioinputs, addressing species diversity, cultivation practices, chemical characterization of bioactive compounds, and their agronomic applications. Literature evidence indicates that K. alvarezii biomass is rich in sulfated polysaccharides, phenolic compounds, photoprotective pigments, fatty acids, and metabolites with hormone-like activity, which have been associated with enhanced plant growth, increased photosynthetic efficiency, and improved tolerance to biotic and abiotic stresses, resulting in productivity gains in crops such as rice, maize, sugarcane, soybean, and vegetables. In addition, biomass represents a potential source of potassium and micronutrients that can complement conventional fertilization. Recent technological advances, as well as regulatory aspects and challenges related to the integration of these products into the global agricultural market, are also discussed. Overall, the evidence highlights the potential of K. alvarezii as a renewable resource for the development of innovative agricultural bioinputs, as biofertilizers and plant biostimulants.