Abstract: Greenhouse and field experiments were conducted to study the competitiveness of invasive plant Flaveria bidentis with native weed plants Digitaria sanguinalis, Eleusine indica, Amaranthus retroflexus, and Abutilon theophrasti. The greenhouse experiment showed that the height growth of F. bidentis was obviously inhibited when the invasive plant was grown at low proportion with D. sanguinalis or E. indica, but not inhibited at equal or high proportion. When F. bidentis was grown with A. retroflexus or A. theophrast, the height growth of the invasive plant was inhibited significantly, but that of the two native weed species was not inhibited. When F. bidentis was grown with the four native weed species, the sum of their relative yields was nearly equal to 1. The relative yield of F. bidentis was nearly to 1 when grown at high proportion with D. sanguinalis, but less than 1 when at equal or low proportion. The relative yield of the invasive weed was significantly less than 1 when it was grown with E. indica or A. retroflexus or A. theophrast. The competitive aggressivity coefficient of F. bidentis was all less than 0 when the invasive weed was grown with any of the four native species. Field experiment showed the same results as the greenhouse experiment did. The findings from this study suggested that F. bidentis and the native weed species utilized the same nutrient resources, and the invasive species was less competitive than the native species when they grew together.

Key words: Rice, Upland cultivation, Water use efficiency, Yield