A Study on Polder Soils in Japan : XII. On the Young Polder Soils of the East Fukuda Polder in Okayama Prefecture.

The purpose of this paper was to study the effects of iron sulfides which had been formed in marine deposits under an anaerobic condition on the chemical compositions and the soil forming processes of soils in East Fukuda Polder. These polder soils examined contained a large amount of soluble salts; especially chlorides constituted the dominant salt among them. Sulfates content was also high and soluble salts appeared to accumulate in surface layers. Air-dried surface soils showed fairly strong acidities, due to the presence of soluble acid compounds formed in the course of oxidation of iron sulfides contained in these soils. The content of FeS2 was found to be between 0.305% and 1.682% as SO3 in the original soils ; and 10% HCl sol. CaO contents were very poor. Soil reactions and soluble salts were determined after the incubation of soils during several weeks at 30℃ under the condition of the moisture content of field capacity. Consequently, in all soils, the pH value became extremely acid, and total solids and water soluble sulfates were greatly increased in the incubated soils; and a relatively good correlation was found between decreased pH values and increased sulfates contents in the incubated soils. It has been concluded that iron sulfides had a marked influence on the chemical compositions of soils and on the prospective soil forming processes of these polder soils.