A unique phenomenon was observed when soybean grew adjacent with Ambrosia trifida, that the nodulation of soybean was remarkably inhibited.In the designed experiment in which soybean grew with or without A.trifida and the soil was spiked with Bradyrhizobium japonicum, the same phenomenon appeared.Soybean has less amount and smaller sizes of nodes when growing with A.trifida, compared with that growing without A.trifida .The same result was obtained in experiment by spraying aqueous extract o...