Influence of Ulva prolifera-derived bio-fermentation extract on cherry radish growth, nutritional quality and soil fertility

Seaweed extracts are widely used as biostimulants and biofertilizers to enhance crop growth and yield. The green-tide-forming macroalga Ulva prolifera represents a promising and sustainable source for such extracts, valorizing a potential ecological burden into a high-value agricultural input in line with circular economy principles. This study evaluated the effects of U. prolifera -derived bio-fermentation (UF) extract on cherry radish ( Raphanus sativus var. radicula ) growth, nutritional quality and soil fertility. Plants were treated with UF extract at concentrations of 5 %, 10 %, 20 % and 30 %, alongside pure water (negative control) and Hoagland solution (positive control), over 40 days. Growth parameters, nutritional quality, and soil properties were assessed. Results showed that low-concentration (5 % and 10 %) UF extracts significantly improved root development and nutritional quality, with the 10 % concentration yielding the highest root weight (5.1 g plant −1 ), anthocyanin (4.3 mg g −1 FW), soluble protein (10.1 mg g −1 DW), soluble carbohydrate (23.4 mg g −1 DW), and leaf pigment contents (0.77, 0.27, and 0.16 mg g −1 FW for chlorophyll a , b and carotenoids, respectively). Conversely, higher UF concentrations (20 %–30 %) diminished these growth-promoting effects, although they increased root vitamin C content, soil nitrogen, phosphorus and potassium (N, P and K) levels, and induced soil acidification. These findings indicate that 10 % UF is optimal for enhancing cherry radish yield and nutritional quality, while highlighting the potential of U. prolifera bio-fermentation extract as a dual-functional plant growth promoter and soil conditioner for sustainable agriculture.