Back to the Origins: Potential of Beach-Cast Macroalgae as Biofertilizer

In the present study, Marine Macroalgae Waste (MMW) biomass, mainly composed of Saccorhiza polyschides , collected from the seashore in northern Portugal, was characterized and seed germination was performed to evaluate the potential of re-exploiting this biomass for agricultural purposes. Kale ( Brassica oleracea L) and parsnip ( Pastinaca sativa ) seeds were used in laboratory assays (23 °C; 10—33 days) to study the effect of using two types of MMW derived products: liquid (water extraction, 0.12 g/mL; diluted at 1.2 vol.%) and solid (after filtering the extract); distilled water was used as control. The germination rate and growth parameters (radicular and aerial part lengths and weights) of the seedlings were further measured. The raw biomass showed promising results for agricultural purposes due to the high carbohydrate content (69.97 ± 0.08 wt.%), mainly composed by fibers (63.4 ± 0.1 wt.%), and the presence of minerals (ash content of 18.54 ± 0.07 wt.%). High amounts of K (2242 mg/100 g), Ca (1886 mg/100 g), Na (985 mg/100 g) and Mg (546 mg/100 g) were found in the ash, with the toxic elements content being within the regulated limits. Seeds germinated better with the liquid extract than with the solid product, with significantly higher ( p