Abstract
1. It was attempted for the control of weeds that dusting of CaCN3 at the rate of 5.63k.g. per are all over the paddy field well prepared were made 5 days before the rice trans-planting into it. This proved to be effbctive for this porpos, the quantity of weed beeing reduced to one quarter of that of unweeded plot. More than 10% of the rice yield of that plot, nevertheless, was decreased as compared with that of the oridinary managed plot, the reason of which may be due to the unrationality of the apilication of CaCN3 as the manure. 2. Application of CaON3 at the rate of 2.81∼5.63 k.g. per are between rows of rice plants in the middle of late ef July was effective for the control of weed. The rice plants were, however injured at the same time, and the yield was consequently decreased about 20% as compared with the contro1, so this method is not practicable. Here, it may bc noted that the rice yield are sometimes increased by the application of CaCN3 at the rate of 1.88k.g. per are with a caution not to fall on the leaves of rice. 3. Weeds of rice field were also killed by the 2% solution of H2SO4 or 20% solution of FeSO4 7H2O, but the rice yield were decreased 5∼lO% by these spraying.
