Assessing Seed Germination and Plant Growth of Eruca vesicaria (L.) Cav. Cultivated in Biochar-Enriched Substrates

This study evaluates the use of biochar as a sustainable substitute to peat in the soilless cultivation of rocket salad (Eruca vesicaria (L.) Cav.). Biochar was added to a peat-based substrate at concentrations of 0% (control), 5%, 10%, 20%, 40%, and 70% v/v to assess its effects on seed germination, plant growth, mineral content, and nitrate accumulation. The results show that biochar concentrations up to 40% v/v maintained germination rates above 80%, similar to the control, while higher concentrations (70% v/v) drastically reduced germination to 29% and entirely compromised plant development and growth. A moderate biochar concentration (20%) had a positive effect on fresh weight and leaf area, while maintaining comparable levels of nutrient uptake, chlorophyll, and flavonols. In addition, biochar-enriched substrates (≥20% v/v) reduced nitrate accumulation in leaves by 26–30%, addressing a critical quality and safety concern. A high biochar content (≥40% v/v) altered the substrate’s physicochemical properties, including pH, porosity, and electrical conductivity, negatively affecting plant growth (a 38% reduction in plant growth and 42% in leaf area) and increasing heavy metal concentrations, such as that of zinc (~30%). These findings suggest that incorporating up to 20% v/v biochar in soilless substrates offers a sustainable alternative to peat, supporting rocket salad performance and improving leaf nitrate quality, without compromising yield or safety.