Effect of Humic Acid on the Seed Germination, Plantlet and Seedling Growth of Summer Vegetables

The application of humic acid (HA) as a biostimulant in vegetable production has gained attention for its potential to enhance plant growth, soil health, and nutrient availability. This study investigated the effects of different HA concentrations (0, 4, 8, and 12 g/kg) on seed germination, seedling growth, and physiological parameters of cucumber, pumpkin, okra, brinjal (eggplant), and tomato under controlled conditions. Results indicated that HA application significantly influenced germination rates, plant height, leaf number, root development, and flowering patterns in a dose- and species-dependent manner. Lower HA concentrations (4 g/kg) improved germination speed in cucumber, pumpkin, and okra, whereas higher doses (12 g/kg) delayed germination or caused seedling mortality in okra and tomato. Root proliferation was enhanced across species, with the highest root numbers observed at 12 g/kg in cucumber and pumpkin. However, excessive HA (12 g/kg) adversely affected okra and tomato, leading to stunted growth or plant death. Brinjal seedlings showed moderate growth improvements with HA, while tomato seedlings exhibited delayed flowering under HA treatment. The findings suggest that optimal HA doses vary by crop species, with moderate concentrations (4–8 g/kg) generally promoting growth, while higher doses may induce stress. This study highlights the importance of tailored HA application strategies to maximize benefits in sustainable vegetable production.