Sulfur and Iron Concentration in Paddy Soils of the Mud-flow Area from the 1926 Explosion of Mt. Tokachi

Abstract

Sulfur and iron concentration were examined in the soils of mud-flow area resulting from the 1926 explosion of Mt. Tokachi. The results are as follows : 1) The new-;lowed soils were made from other soils after the explosion, and the soil layers were from 14 cm to 30 cm in depth. 2) The depths of the mud-flows were from 7 cm to 145 cm under the new-;lowed soils. This indicated almost the same values in the mud-flow depth compared with similar data obtained just after the explosion. 3) The pH ranged from 4.9 to 6.2 in the new-;lowed soils, from 4.1 to 6.2 in the mud-flows. The averages of the pH were 5.65±0.33 in the new-plowed soils, and 5.28±0.70 in the mud-flows. The soil pH was in inverse proportion to total sulfur concentration in the all soil samples. 4) The averages of total sulfur concentration were 6.3±3.3 g kg^<-1> in the new-;lowed soils, 13.6±10.6 g kg^<-1> in the mud-flows and 13.1±14.2 g kg^<-1> in the old-plowed soils. The highest value of the total sulfur concentration was 77 g kg^<-1> in the peat of the old-plowed soil. 5) Electric conductivity increased proportionately with soluble sulfur (SO^<2->_4) concentration in soils, and the coefficient of correlation obtained a high value of 0.947 for all soil samples. 6) The original new-plowed soils had a high value of 0.947 for all soil samples. 6) The original new-plowed soils had a sulfur concentration of less than 0.10 g kg^<-1>. And it was supposed that the old-plowed soils had less than 1.0 g kg^<-1> of sulfur concentration before the explosion. Therefore, high sulfur concentration in the new-plowed soils and in the old-plowed soils was due to high sulfur in the mud-flows during the past 65 years. 7) The total iron concentration (agur regia soluble) showed little change, but the concentration of free-ferric oxide in each of the soil groups differed significantly. The free-ferric oxide level decreased with the increased sulfur level. There was no sample in which free-ferric oxide concentration was more than 7 times the sulfur concentration in the new-plowed soil ( molar rate).