Influence of barnyardgrass (Echinochloa crusgalli BEAUV. var. oryzicola OHWI) on the productivity of paddy rice (Agriculture)

水稲の生産性におよぼすタイヌビエの影響をみるために, タイヌビエの発生時期や生育期間を人為的に変化させて検討した。すなわち, 熟期の異なる水稲2品種の種々の生育時期にタイヌビエを混植あるいは除草することによって, タイヌビエとの競争による水稲の減収要因を生長解析によって分析した。その結果, いずれの競争区においても水稲の収量は単植区よりも減少し, 両植物の競争期間が長いほど, また, この競争が生起する生育時期が早いほど減収率は大きかった。この収量減を収量構成要素の面よりみれば, 1穂重の減少によるよりも, むしろ穂数減に起因するところが大きく, さらに, 水稲の乾物生産性の面から分析すれば, 生育初期におけるNARと出穂期以後におけるCGRの低下によるものと推察された。一方, 水稲品種の早晩性よりみた場合, タイヌビエの影響は晩生品種におけるよりも早生品種においてかなり大きくあらわれた。
The influence of the weed barnyardgrass (Echinochloa crusgalli BEAUV. var. oryzicola OHWI) on the productivity of paddy rice was investigated in relation to emergence time and growing period of the weed. Twelve day-old weed seedlings were transplanted 10,30 and 50 days after transplanting of the two rice varieties which differ in maturity date. The weeds which had been transplanted 10 days after transplanting the rice were hand-weeded at various times. The factors causing reduction in rice yield due to competition with the weed were examined by growth analyses. In all the competition plots rice yield was smaller than in the single cropping plot and, in general, the longer was the competition period of the two plants and the earlier the beginning of the competition, the larger was the yield reduction rate of rice. These reductions of rice yield were caused largely by the decrease in the number of panicles rather than in the panicle weight, and it was infered further that the reductions were attributable to the decrease in net assimilation rate in the early growing stage and in crop growth rate after heading. It was also recognized the influence of the barnyardgrass on the rice productivity was larger in the early-maturing variety than in the late-maturing one.