Phytotoxic potential of soils and wheat straw in rice rotation cropping systems of subtropical Taiwan

Using a wheat seed bio assay, the phytotoxicity of extracts obtained from wheat and rice rhizosphere soils was determined. The wheat rhizosphere soil extract was found to show phytotoxic effects. More allelopathic materials were found from the wheat-rice rotation soils than from the rice soil. Extracts obtained under basic conditions (pH 8) were found to be more inhibitory than those obtained by acid extraction (pH 5). Wheat straw was found also to contain phytotoxic substances. A comparison of two methods in concentrating the aqueous extracts, rotary evaporation and lyophilization, indicates that the former contained more substances with phytotoxic effects.