Valorization of Macroalgal Biomass into Biostimulants and Biofertilizers for Sustainable Agriculture

The growing need for sustainable agricultural inputs has sparked interest in the valorization of macroalgal biomass into bioproducts such as seaweed-based biostimulants and biofertilizers (SBBFs). SBBFs derived from macroalgae such as Ascophyllum nodosum and Gracilaria spp., offer a promising solution to enhance crop productivity while reducing ecological harm. Rich in bioactive compounds—including polysaccharides, phytohormone analogs, and antioxidants—SBBFs improve soil health, nutrient efficiency, and plant resilience to abiotic stress. This review integrates bibliometric and systematic analyses of 969 articles (2003–2024) to evaluate global research trends, biological mechanisms, and environmental applications of SBBFs. Research output has expanded rapidly, from < 15 articles annually before 2014 to 166 in 2023. Leading contributors include India, Italy, and Poland. Keyword clustering identifies five core research themes: (1) biostimulant mechanisms, (2) antioxidant roles, (3) yield enhancement, (4) stress tolerance, and (5) macroalgae cultivation. Thematic evolution shows a shift from foundational studies on nutrient assimilation to applied research on stress tolerance and extraction technologies. Empirical findings confirm that SBBFs enhance photosynthesis, nutrient uptake, and root development. Field studies demonstrate yield improvements (e.g., + 49% in drought-stressed tomatoes) and improved stress resilience via osmotic regulation and antioxidant defense. Key challenges remain, including variability in formulation, regional research disparities, and a lack of standardized protocols. This review underscores the dual role of SBBFs as productivity enhancers and ecological solutions and proposes three research priorities: (1) multi-omics-based mechanistic studies, (2) global meta-analyses, and (3) circular economy integration. Collectively, these insights position SBBFs as strategic tools in sustainable land use, agro-environmental restoration, and climate-resilient ecosystem management.