The Impact of Varying Biochar Rate and Particle Size Derived from Bamboo Culm Residue and Coconut Husk Mixture on Lettuce (Lactuca sativa cv. ‘Tiberius’) Seed Germination and Leaf Morphology

Background: Lettuce cultivation, known for its high germination potential, can benefit significantly from soil amendment practices like biochar application. This study investigates the influence of varying biochar application rates (30 t/ha, 15 t/ha, and 7.5 t/ha) and particle sizes (≤0.5 mm and ≥2 mm), derived from a blend of bamboo culm sheath and coconut husk, on lettuce seed germination and leaf morphology. Methods: The field experiment utilized a factorial design within a Randomized Complete Block Design during the 2021/2022 major and minor cropping seasons. Results: Results revealed that biochar addition significantly enhanced soil properties, including organic carbon, total nitrogen, phosphorus, potassium, pH, and moisture content (p < 0.05). Notably, seeds sown in soil amended with 15 t/ha of biochar exhibited the longest Mean Germination Time (MGT) (4.3 ± 0.19 days) and lowest Germination Index (GI) (646.3) compared to those in soil with 30 t/ha fine biochar (MGT = 4.0 ± 0.03 days; GI = 668.7). Lettuce grown in soil treated with 30 t/ha of fine biochar displayed the longest leaves (17.42 ± 0.12 cm), whereas plants from soil with 15 t/ha coarse biochar had the shortest leaves (13.8 ± 0.17 cm). Leaf width followed a similar trend. Surprisingly, the cropping season did not significantly affect lettuce seed germination and leaf morphology. However, moisture content emerged as the most influential property of biochar-amended soil on lettuce seed germination. Conclusions: These findings underscore the potential of biochar-based lettuce farming to enhance soil health, germination rates, crop growth, and overall productivity. They provide actionable insights that contribute to sustainable agricultural practices and food security.