Stimulation of seedling root growth by coal-derived sodium humate

Coal-derived sodium humate was found to stimulate primary root growth of seedlings of cantaloupe (Cucumis melo L.) at 1000 mg L^–1, lettuce (Lactuca sativa L.) and onion (Allium cepa L.) at 500 and 1000 mg L^–1, as well as hypocotyl growth of cantaloupe at 1000 mg L^–1. Growth enhancement was not due to release of nutrient elements by the product, and, in the case of lettuce and onion, was not due to increased availability or uptake of mineral elements. Growth stimulation of cantaloupe, however, was dependent on the provision of nutrient solution. Growth stimulation of onion roots under axenic conditions indicated an effect of the humate per se rather than a response mediated via microbial breakdown products.