Effects of timing and soil moisture on the allelopathic activity of itchgrass (Rottboellia cochinchinensis) in soil

Farmers in the Chaehom-Lampang area of northern Thailand use itchgrass [Rottboellia cochinchinensis (Lour.) W. D. Clayton] as a mulching material for weed control in vegetable crops. Almost all allelopathic activity due to the release of allelochemicals from itchgrass occurs in field conditions. Therefore, the phytotoxicity of soil amended with itchgrass powder was investigated under laboratory condition. To examine residual allelopathic activity, five application times (0, 15, 30, 45 and 60days after incorporation [DAI]), powder of two itchgrass parts (shoot and root) and three concentrations of each powder (0, 0.01 and 0.1gg(-1) soil) were tested. To determine the effect of soil conditions on allelopathic activity, five application times (0, 15, 30, 45 and 60DAI), powders of two itchgrass parts (shoot and root) and three soil conditions (dry, half-saturated and submerged) were tested. Incorporating itchgrass powder into the soil had inhibitory allelopathic effects on the growth of Ageratum conyzoides L. and Echinochloa crus-galli (L.) Beauv. and the effectiveness was intensified with increased concentrations of itchgrass powder. The allelopathic activity of itchgrass in soil persisted for a maximum of 15DAI and then decreased over time. The allelopathic activity of itchgrass was the highest under dry conditions followed by half-saturated and submerged conditions. These results suggest that the allelopathic activity of itchgrass is influenced by timing and soil moisture condition.