Abstract
It is regarded as weeds in the row that have the largest relation to the competition between crops and weeds, but the influence of weeds in the row was showed not to be so large as we expected. Especially, when weeds between the row were eradicated, weeds in the row did not exert any appreciable influence on the crop yield. Those weeds as Chenopodium album, Polygonum orientale and Amaranthus Blitum, that grow very rapidly, gave the largest reductions in crop growth. So, it would be the shading by weeds and not the competition for nutrition that principally brought about the crop damage. On weeding in the upland rice field these points must be kept in mind and weeding at two periods, few weeks after germination and the stage of flower bud differentiation, would be resulted in less reduction of the upland rice yield.
