Influence of Walnut Shell Biochar and Fertilizer on Lettuce Production in Hydroponic and Conventional Systems

Water scarcity and soil fertility loss are major limitations for agricultural production. This study evaluated the effects of walnut shell biochar (WSB) and fertilizer on the growth of lettuce (Lactuca sativa L. “Gran rapid”) in hydroponic and conventional systems. WSB alone and WSB + fertilizer were applied at different mass ratios to soil (0, 5, 10, and 15%) in the conventional system and to the substrate (0, 10, and 20%) in the hydroponic system. Agronomic parameters such as fresh weight, dry weight, leaf area index, and the number of leaves were evaluated. The results showed that fertilizer addition improved growth in both systems. In hydroponics, the combination of WSB and fertilizer increased fresh weight by 45% and dry weight by 38% compared to the control without biochar or fertilizer. In the conventional system, WSB alone increased fresh weight by 30% and the number of leaves by 25%, without requiring additional fertilizer. Lettuce grown in conventional soil with 15% WSB and fertilizer achieved a 1.8 times higher leaf area index than the control without biochar. These findings suggest that WSB and fertilizer applications enhance lettuce crop yield, supporting the principles of circular economy and sustainable waste management in agriculture.