サイパン, テニアン及ロタの土壌に就いて : 第一報現地調査及器械的分析之部

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(1) In the Saipan, Tenian and Rota Islands, the climate is moderately hot through the year, and is sharply divided into rainy and dry seasons. Lang's rain factor is 69,and Meyer's N-S factor 290. (2) Every island consists of elevated coral reef which has been formed on the submarine volcano, showing a characteristic topography of terrace-land. The ground rocks, such as liparite and andesite, and the sedimentary rocks except limestone are exposed in a few places, occupying a small area. The greater parts of every island are covered with various sorts of limestone. Among them, the recently formed, Mariana limestone predominates. (3) The island-solis are almost invariably clayey, and the most of them, may be regarded as residual soils. The soil layer is generally thick with some exceptions. The surface horizon is dark or black through the presence of certain amounts of humus, possessing a granular structure, while the subsoil horizon is yellow, red or brown in color, the structure being varied with the nature of soils. The main island-soils may be classifyed as follows : I Limestone soils 1. Brown colored soils 2. Yellow colored soils 3. Red colored soils 4. Friable soils of Rota II Soils from volcanic rocks and sedimentary rocks excluding limestone 1. yellow solis 2. Red solis (4) The brown colored limestone-soils occur in Tenian and Saipan, occupying greater parts of the sugar cane plantation. The solis are composed of soft clay of homogeneous appearance throughout the vertical section. The top horizon is dark in color and loose in constitution, possessing a granular structure, whilst the subsoil horizon is brown and firm, possessing no particular structure. The drainage of the soil layer is good. The subsoil horizon lies directly on the parent rock, Mariana limestine, which has numerous, irregular, so-called "pocket" holes of varying width and depth on the surface. (5) The yellow colored limestone-soils also occur in Saipan and Tenian. The parent rock is in some places, impure or hard limestone of tertiary formation, while in other places, it is Mariana limestone. The subsoil horizon is in general, composed of yellowish, tenaceous, compact clay, often involving black spots or soft concretions of ferro-manganese deposition. The permeabiliy of water and air is not good. This horizon gradually merges into the underlying horizon of low degree of weathering, which has white streaks and bands on the profile plane of pale yellow coloration. (6) The red colored limestone-soils have probably been developed from the yellow colored soils by laterization after reclamation. They occur on hills in Saipan and Tenian. The soil layer is composed of brownish red clay, tinged with purple, of homogeneous appearance throughout the profile, resembling Terra Rossa. Drainage and constitutional characters are medium as compared with the two soils above-mentioned. Often it possesses the irregularly-block or prismatic structure. The soil layer lies directly on the parent limestome (7) The limestone soils of Rota are characterized by having markedly friable and loose properties. The soil layer is generally thin, composing of light clayey material. It is very loose in compactness throughout the profile. The parent rock is mainly Mariana limestone which has many "pocket" holes on its surface. The soil on the lowest plain of the terrace-island is yellowish brown in color, but it becomes deeper and more red with increasing elevation of the plain. (8) Whilst the liparite soils soccur only in Saipan, the andesite soils are found in every islet of the three. The latter class is probably the most productive in the islets. The soils from tertiary formation except limestone, mainly occur also in Saipan, and none in Rota. The surface horizon of this group of soils is, in general, dark in color and granular or orumb in structure, overlying the subsoil horizon which is yellowish and mostly structureless in the cases of yellow soils, or is reddish in the cases of red soils. The red solis generally occur on hills or dry places, sometimes possessing a nuttty-like, block, or prismatic structure. They may be regarded as derivatives from the yellow soils. (9) The results of the mechanical analysis indicate that almost all soils contain markedly large amounts of clay fraction, the coarser fractions being correspondingly small. Gravel portion is rarely found. As a general tendency, it is seen that the clay content of the surface horizon is smaller than that of the subsoil horizon. (10) The limestone soils of Rota contain fairly large quantities of fine sand and silt instead of clay, indicating that the soils are relatively in early stage of weathering. The solis from volcanic rocks and non-calcaleous rocks of tertiary formation contain noticeable amounts of quartz and iron sands. (11) All of the island soils have high water-capacity. The capacity of the limestone soils is, however, obviously lower than that of the other soils, with an exception of Rota soil whose capacity is as high as that of the other soil groups.
1940-07-25

サイパン, テニアン及ロタの土壌に就いて : 第一報現地調査及器械的分析之部

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サイパン, テニアン及ロタの土壌に就いて : 第一報 現地調査及器械的分析之部

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サイパン, テニアン及ロタの土壌に就いて : 第一報現地調査及器械的分析之部