Bio-product as a nutritional approach for sustainable hydroponic lettuce cultivation

Hydroponic plant production continues to expand, largely relying on chemical fertilizers for nutrient supply. In contrast, small-scale hydroponic systems for organic vegetable cultivation still require technological development and suitable inputs. This study aimed to evaluate the production of organic lettuce (Lactuca sativa L., cv. Simpson) using different concentrations of a liquid bio-product in a sustainable small-scale hydroponic system built with recycled materials. The experiment was conducted in São Lourenço do Sul/RS, from October to November. Lettuce seedlings, 15 days after emergence, were transplanted into 2 L containers with nutrient solutions containing 0, 6.25, 12.5, 25, and 50 ml L⁻1 of a liquid bio-product made from chicken manure, coffee grounds, wood shavings, brown sugar, and wood ash. Chemical characterization of the solutions, including pH, electrical conductivity, and macro and micronutrient content, was performed at the beginning and after 20 days. After 40 days, plants were harvested, and root and shoot dry mass was measured. The 50 ml L⁻1 concentration promoted the best results, significantly improving plant growth parameters such as root and shoot development, leaf area, and total biomass. Plants also showed increased uptake of nitrogen, phosphorus, and potassium. These findings demonstrate that the bio-product can serve as an effective and eco-friendly alternative to conventional hydroponic nutrient solutions, especially for organic production. The results highlight the potential of bio-products to support sustainable agricultural practices, reduce dependency on synthetic fertilizers, and improve the quality of crops grown in hydroponic systems.