Allelopathic effects of legume cover crops on cogon grass (Imperata brasiliensis Trin.).

Seed leachates and water extract of residues of jackbean (Canavalia ensiformis L. DC.), velvetbean (Mucuna pruriens var. utilis L.) and kudzu (Pueraria phaseoloides Roxb.) were examined for effects on germination of cogongrass (Imperata brasiliensis Trin.). In order to evaluate the effects on development and NPK content of the whole plants, cogongrass were grown in presence of root exudates of the cover crops. Germination tests stressed the inhibitory effect of jackbean that reduced weed germination by 12% using undiluted seed leachates. Shoot residues of all cover crops promoted germination by a mean of 6% while germination index was remarkably delayed of 22 and 26% with the highest levelò of extract of velvetbean and jackbean respectively. Notable and significant increase of fresh weight (+142% compared to control) was observed with the highest root extract of jackbean. Growth of cogongrass was significantly reduced by root exudates of jackbean and velvetbean. A strong effect was recorded for leaf area with a reduction of 46 and 26% in presence of root exudates of Canavalia and Mucuna respectively. Canavalia could be considered an important cover crop for cogongrass replacement in the humid tropics. The allelopathic influence of jackbean is notable starting from the seed imbibition by releasing substances affecting germination of I. brasiliensis.