Abstract
It is recently observed in Kagawa & Okayama prefecture in Japan that paddy field rice plant is often damaged in late July & early August when the season gets hot especially after the top-dressing with am-sulfate & etc. From the inspection of the field the authors suppose that the damage have a close connection with the reduction of am-sulfate & other sulfate-manures applied to soil and tested the reduction of several sulfates in soil of paddy field condition. The results will be summarized as follows; 1. All the soil sampled from the damaged field, reduces sulfate well. 2. The reduction is increased; a) with the amount of sulfate applied. b) with the temperature of incubation, especially above 30℃. c) with pH of soil especially at slight alkaline & neutral and at about pH 3 it stops. d) with the water content of soil. 3. The soil reduces each of Am K. Na. & Ca-sulfate almost equally but not Cu-sulfate. 4. Desinfection stops the reduction. 5. From the above results, the authors conclude that the chief cause of the damage may due to the sulphide formed in soil by the reduction of sulfate manures applied to soil.
