Abstract:In the present paper,competitive effects on Oryza rufipogon,Ranalisma rostrata and Isachne globosa populations were studied by orthogonal designed experiment of three species factors and five planting density levels.The results showed great disadvantages for each of the three mixed crops,the bigger the initial density was,the greater the negative effects were.Each population was sensitive to inter specific competition,while intra specific competition should also not be ignored. O.rufipogon ...