Abstract
(1) In 1946, in order to recognize the result of previous report again the experiment were carried out at the paddy field where the rice plants were transplanted on July 2nd and only one time weeding was done with hand weeding machine before the spray. (2) Na-2.4-D which was made in U.S.A. and two chemicals which were made in Japan, were used for this test. (3) On July. 28th or Aug. 8th 2.4-D of 40-60g which were disolved in water of 75 litres were sprayed per 10 ares after drained. The area of every test plots are 1/5 are and some treatment had repeated in four plots, and as a cotrast 4 times band weeding plot and no-weeding plot were set up. And the effect of weeding on the paddy field and on the yield of rice were investigated. (4) On July 28th when 2.4-D of 40-60g were sprayed per 10 ares the weeds were all killed except graminous such as Echinochlola Crus-galli BEAV. and Leptichla chinensise NEGS. within 10 days, and this effect for weeding are equal to that of 4 times by hand. This is a proof of the remarkable weeding effect of 2.4-D. (5) On the other hand, in case of spraying of 2.4-D of 40g on July 28th. there is no damage in growth of rice plants, and from this on treated plot there were the same yield of rice as compared with the plot which were weeded 4 times by hand, although, formers were little inferior to the latter in plot to the number of tiller and the weight of stalks. This fact was all alike the result of the last year. (6) In the plots which were sprayed 2.4-D of 60g, slight injury was appeared in growth of rice plants and weights of grains of each rice plants is dainger of decrease. Therefore, the use of 40g is suitable. (7) The yield of rice, at the plot in which 2.4-D of 40g was used on Aug. 8th, decreased and this was because that as the weeds grew closely before the spraying, the growth of rice plants were checked. (8) From above mentioned result, it can conclude that, at rice paddy fields, application of 2.4-D of 40g per 10 ares can practically use.
