中国北東部における水田土壌と畑土壌の粘土画分中の鉱物組成の比較

抄録

We clarified the chemical composition of the clay fraction and the clay mineral composition using an X-ray diffraction meter for three kinds of paddy soil samples which were taken from fields in JinLin Province, northeast China, which is a cold and semi-arid area. Then, we examined the influences of the climate in this region on the composition of clay minerals with the paddy soil formation comparing it with a case of respective upland soils. The results are summarized as follows. 1) All samples contained quartz and feldspar. Quartz and feldspar in the clay fraction of the paddy soils developed from Cambisol and Planosol-type upland soils contained much more than that of respective upland soils, but they contained almost same level in paddy soils developed from Luvisol. This difference seems to come from the influence of soil water circumstance, freezing and melting reactions on soil conditions after surface drainage. 2) The main clay mineral composition was different in three kinds of paddy soils. Montmollironite and illite were dominant in Cambisol-type paddy soil, illite and vermiculite were dominant in Planosol-type soil, and illite was dominant in Luvisol-type soil. These differences in clay mineral composition were considered to be due to the differences in parent materials, metamorphism by the eluviation of potassium and its enrichment. 3) The main clay mineral composition in the same paddy soil profile was uniform, any changes in the composition of clay minerals of the plough layer in the paddy soil formation were therefore recognized. 4) The main clay mineral composition was the same in the paddy soil and its respective upland soil. This fact shows that there were no changes in the clay mineral composition in the older paddy soil several decades after development as compared to the upland soils, and that the influence of the original clay mineral composition is strong in this area.