A Sustainable Microalgae-Based Biostimulant Enhances Soybean (Glycine max) Germination and Early Seedling Growth

The transition toward sustainable agriculture requires innovative biostimulants that enhance crop performance while reducing reliance on synthetic agrochemical inputs, such as mineral fertilizers and chemical pesticides, including herbicides, insecticides, and fungicides. Microalgae have gained considerable attention as sustainable biostimulants due to their diverse biochemical composition, including primary metabolites, phenolic compounds, and phytohormones. This work examined how Chlorococcum sp. extract influences seed germination, early seedling development, pigment content, and biochemical composition of soybean (Glycine max L.). Biochemical characterization of the extract revealed it was rich in polyphenols and flavonoids. Seeds were treated with four concentrations (0.1–2 g L−1) and compared to an untreated control. The extract significantly improved the final germination percentage, from 57% in the control to 70% (0.5 g L−1) and 80% (1 and 2 g L−1), with a similar trend observed for the seed vigor index. Radicle and hypocotyl lengths increased significantly. Results also showed that pigment levels increased, especially under the 0.5 g L−1 treatment. Seedling biochemical parameters, including carbohydrates, proteins, reducing sugars, phenolic compounds, and DPPH radical-scavenging activity, increased under microalgal treatments. Overall, the findings highlight the potential of microalgae-derived biostimulants as renewable and environmentally friendly alternatives to conventional crop inputs, supporting more sustainable soybean production and contributing to the development of resilient and resource-efficient agricultural systems.