Algae Extracts in Horticulture: Characterization of Algae-Based Extracts and Impact on Turnip Germination and Radish Culture

Algae are rich in nutrients and bioactive compounds, playing a crucial role as biostimulants for plants, enhancing growth and resilience. Four algae-based extracts were tested: the raw extract of red macroalgae Calliblepharis jubata (CJ), Ulasco (UA), Grasco (GR) and “AgriAlgae Foliar” (AA), the latter with microalgae. The extracts were evaluated for their physicochemical parameters (pH, electrical conductivity and solids), macro and microelements, phenolic compounds and antioxidants. Afterwards, seed germination trials were carried out with turnip seeds (Brassica rapa var. cymosa L.), and pot trials were carried out with Cherry Belle (Flora Lusitana, Cantanhede, Portugal) radish plants (Raphanus sativus L.), to verify the biostimulant potential of the extracts in horticulture. In the pot trials, all the treatments led to better yields and nutritional quality. The UA 0.12 extract influenced the heaviest roots (40.32 ± 11.89 g), on average, and the GR 0.10 extract in roots with the highest percentage of proteins (1.866 ± 0.004% dm), phenolic compounds (0.12121 mg eq. gallic acid/g fm) and antioxidants (0.0754 ± 0.0000 mg eq. ascorbic acid/g fm). The radishes treated with the AA 0.003 extract showed the greatest uniformity, the healthiest leaves, with the highest flavonoid content and the heaviest aerial part (19.52 ± 5.99 g). All the extract treatments resulted in a visible mitigation of abiotic stress and consequently better results, showing that these can be crucial for sustainable agriculture.