Abstract
The authors have already reported that chief cause of the damage in paddy rice field in Kagawa and Okayama prefectures in Japan by am-sulphate manuring, may due to sulphide-formation by the reduction of the manure. The authors continued the experiment in regard to this problem on the relation between redox-potential of soil and the reduction and the results will be summarized as follows; 1. The soil such as its redox-potential is markedly lowered when it was kept under stagnation, reduces sulphate without exception and the reverse is also true. 2. The above lowering of the potential is accelerated a) by the rise of incubation-temperature and b) by the increase of pH of soil by liming. 3. The above acceleration was also proved in the case of sulphate-reduction. 4. The low redox-potential of the damaged soil during summer, gets higher with the elapse of season and in the middle of october when the field was drained, the value reaches almost to that of undamaged soil and the amount of sulphide decreases parallel with the above change of the potential during seasons. 5. The fact shown in 4,indicates that the potential and the amount of sulphide of soil, are not stable but change with the amount of water in rice field.
