開拓地の不良土壌に関する研究(第5報) : 島根県波根湖干拓地の土壌について

抄録

In May, 1950,the Hane-Ko polder was drained by means of pumping up, and immediately after the drain rice plants were transplanted on it, and good harvest was gained in the fall of 1950. In 1951,the second year of planting, however, the growth of rice plants were seriously damaged.An area of damaged region amounts to about 100 acres which occupy about 80 per cent of the total field area. In order to know the causes of the damage for rice plants grown on the Hane-Ko polder, the author investigated some chemical properties of the polder soils and recognized the following facts : 1) Though the soil favorable for the growth of rice plants are neutral in reaction, the soils of rice field subjecting to the serious damage show the extremely strong acidity of pH 3.0 or below. 2) When both acidified and non-acidified soils were incubated at 30℃ for two weeks under the condition which is approximately the same as the mositure content of field capacity, both soils, in spite of the remarkable difference in reaction, showed the extremely strong acidities of the pH range from 2.0 to 2.6 After incubation free acid increased, to a great extent, that is, free SO_3 contents became 0.460 to 0.762 per cent on dry matter (105℃). 3) Sodium chloride contents of the polder soils are 0.072 to 0.156 per cent on dry matter (105℃). 4) Leaves of the damaged rice plants showed grayish black or brownish black coloration according to ferrosulfate containing in the acidified polder soils. The author has concluded from the facts mentioned above that in 1951 the damage of rice plants was attributed to the extremely strong acidity owing to the acidic components, such as ferrosulfate, aluminium sulfate, free sulfuric acid and other, which are produced by the oxidation of ferrosulfide containing originally in the polder soils.