プレーリー地帯に於ける土壌の局部的ポドゾール化について

ミゾリー州ホワード郡内における観察

抄録

The U. S. Department of Agriculture, Bureau of Chemistry and Soils has devided the land of the U. S. A. into twelve soil types in zonal soil groups. According to the soil types, the best farming soils are the prairies soils of the middle west and gray-brown podzolic soils to the east of the prairies.
The writer had an opportunity to observe the soil profiles in Howard County of the prairies on the west side of the gray-brown podzolic soil region. The prairies are covered by loess. Loess is a silty, windblown deposit during glacial times which at the time of its deposition was mineralogically rich. Its presence in Howard County accounts for most of the better upland soils. Thickest deposits are around Glasgow and in a narrow band following the Missouri River bluffs. The loess thins to the east and north but, even so, most ridgetop soils in north-eastern part are formed of a thin mantle of loess over glacial till. The thicker the loess mantle, the less weathered is the soil and the less clay in the subsoil. The loess has been eroded from most slopes, but is found on increasingly steeper slopes as one approaches the river hills. Generally speaking, on the slope and in the river and river bottomlands, the surface soils and also subsoils are leached showing gray-white or gray-brown colour in the soil profiles, which can be classified into podzolic soils. Even in the prairies, the river bottomlands under circumstances of the humidity, and the thin mantle of loess, will be podzolized in the soil profiles.
The writer's thanks are due to Prof. W. D. Keller of the Institute of Geology, Prof. C. E. Marshall of the Institute of Soil Science and Dr. Caldwell of the Counsellor to the Foreign Students of the University of Missouri, for their help and suggestions, and he also appreciates the kind help he received in his field work from Mr. Rae of the Soil Conservation Committee and Mr. Mann from the same county.