Crude extracts of seaweeds (Ulva lactuca and Eucheuma spinosum) as biostimulants for enhancing sweet pepper production

Sweet pepper is the world’s second most important vegetable after tomato, making its production vital for economic growth and supporting livelihoods. However, growing concerns about environmental protection and sustainability make the search for eco‑friendly alternatives to synthetic fertilizers inevitable. Seaweed extracts are rich in bioactive compounds that can stimulate key plant growth and defense pathways making them effective biofertilizer. A Randomized Complete Block Design was laid out to evaluate the potential of seaweed extract (U. lactuca and E. spinosum) in promoting the growth and productivity of sweet pepper(Capsicum annuum L.). Seaweed was applied in both liquid and in powder form. The liquid extracts were prepared by soaking 15 g, 20 g, 25 g, and 30 g of seaweed powder in 1 L of hot and cold water, while the powder was applied directly without dilution. The negative control group received no seaweed treatment. Both Nonparametric and parametric comparisons for the growth and yield parameters were performed. Results showed that seaweed significantly increased the average fruit weight (792%), fruit number (100%), number of branches (114.3%), and number of leaves (51.7%), stem girth (20%) and plant height (50.2%), with variations depending on the extraction method, seaweed species, and concentration. The optimal seaweed extract concentration was 0.6% beyond which no significant increase in growth or yield of sweet pepper was observed. Mean separation revealed that cold-water extraction had the most pronounced effect. In conclusion, this study highlights the importance of incorporating seaweed as biostimulants in a closed-system agriculture. However, further research should explore the extracts long-term effects, refine application and scalable methods for mass production and consistent quality and evaluate its efficiency in open-field agriculture.