Abstract
1) Tests were made on (1) germination of barnyard grass seed, (2) tolerance of the young barnyard plants to submergence in water, and (3) the effect of flooding on the top and root growths of the rice plants and its yield. 2) Rice plant were planted on June 28th, 1950 in concrete boxes, having glass wall on one side. On July 5th all weeds were removed and seeds and seedlings of the barnyard grass were planted between the rice plants. The amounts of water of respective boxes were adjusted to soil saturation and 5, 10, 15 and 20 cm. deep. Their conditions were held for 15 and 30 day periods and then all plots were flooded 5 cm. deep to mature. 3) With the increase in the depth of water the germination of the seeds of barnyard grass decreased. But in the laboratory, Tainubie (Echinochloa Crus-galli BEAUV. var. oryzicola OHWI) showed a considerable germination even at 15∼20 cm depth of water. 4) Many weeds that grew in paddy fields showed more or less tolerance to submergence, in water even when entirely submerged. Most of barnyard grass died after having been entirely submerged in water of 20 cm. for 15∼30 days. In the case of 15 cm. depth, a few plants survived. Barnyard grass developed the best on the saturated soil and next best in soil submerged for 5 cm. 5) Rice plants also showed considerable tolerance to water. The yield from 10∼20 cm. depth was equal to that of 5 cm. depth. As to the number of tillers, the treatment of 20 cm. of water held for 15∼30 days was momentarily poorer than the 5 cm. and rice plants tended to lodge. 6) The growth of rice plants on the saturated soil was inhibited on account of much weed growth and therefore its yield was small.
