Abstract
Laboratory experiments were conducted to determine the phytotoxic activity of water leachates from Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray] leaves and the effect of water movement on efficacy of the leachate in soil. The water leachates from both the green and senescent leaves applied onto soil inhibited root growth of rice seedlings. The phytotoxicity of leaf leachate depended on the concentration of phytotoxic substances which was determined by the amount of leaves extracted. Mobility of phytotoxic substances from Mexican sunflower leaves in soil was dependent on water movement and soil moisture conditions. More downward movement was observed in dry soil than in wet soil. The inhibitory activity of water leachate in soil was well correlated with the concentration in soil-water. The allelopathic potential of Mexican sunflower leaves in natural field was discussed.
