水稲の雑草害に関する研究 : 水稲の生育,収量並びに生態条件に及ぼすタイヌビエの影響

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Over a period of two years, 1965 and 1966, the degree and pattern of the damage to riceplants due to the competition with barnyardgrass at the nine stands of 0, 2, 5, 10, 20, 40, 80, 160, and 320 per spuare meter were studied under two fertilizer levels and on three rice densities. The results are summarized as follows : 1. Ths height of rice plants, when coexisting with a higher number of barnyardgrass stands, tended to increase during the middle stages of the growing season. The number of tillers of rice plants was reduced seriously owing to coexistence with barnyardgrass. However, the tillering until around late July was not so detrimentally affected, but that after early August was so seriously done, and the number of tillers with panicles was reduced by about 50 per cent at the harvest time. 2. An injurious effect on the heading of rice plants was scarcely found. However, when rice plants grew together with barnyardgrass at the highest number of stands, they delayed one or two days in the heading time. In addition, stunting of the heading was found in some of the rice plants in 1965. 3. The yield of rice plants was reduced more seriously as the stands of barnyardgrass increased, being in a curved negative regression against the Logarithm of the number of barnyardgrass stands. The percentage of reduction varied considerably according to fertilizer levels and rice densities, so that it was impossible to express the relation of the rice yield to the number of barnyardgrass stands by only one emperical formula. But its relation to the barnyardgrass weight was expressed by the following formula : log Y= a-bX (Y, X, and a, b are barnyardgrass wt, index of rice yield, and constants, respectively.), irrespective of fertilizer and rice density condition. 4. The components contributing to the reduction of rice yield were the number of panicles, the weight of grains, the number spikelets per a panicle, and the fertilization percentage of the spikelets in the order of decreasing importance. 5. In a mixed population of rice-barnyardgrass, the reduction of incident light, the change of the productive structure of rice population, the decreasing of LAI and dry weight of leaves, and the lowering of nitrogen content of upper leaves were found, A difference between rice and barnyardgrass in their absorbing pattern for the nitrogen element was observed, so that it was proposed that the competition for nitorgen uptake between both plants should be more serious during the first half of the growing season.
日本雑草学会の論文
1968-12-25

水稲の雑草害に関する研究 : 水稲の生育,収量並びに生態条件に及ぼすタイヌビエの影響

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