On the Soils of the Saipan, Tenian and Rota Islands, Mariana. : Part II, Chemical Analysis.

Abstract

1. The carbon content in 36 surface soils of all sorts, varied from 1.2 to 7.4 per cent, the average being 33 per cent. The average value for the carbon : nitrogen ratio was found to be 11.4. 2. Rota limestone-soils are saturated with calcium, the pH values being near 7 or more. They have no exchange acidity. The base-exchange capacity is extremely low. The colloidal clay-fraction has such silica : sesquioxide ratios as low as 0.2. The corresponding ratios for the fine soil are also nearly the same. The soils contain appreciable amounts of lime and magnesia, indicating that the leaching is still incomplete. 3. Brown-colored limestone-soils are nearly saturated with calcium. The pH values are about 7 or less. Resembling the Rota soils, they have no exchange acidity but low hydrolytic acidity. The colloidal SiO_2/R_2O_3 ratio is approximately 1.0,the SiO_2/Al_2O_3 ratio being 1.2. The corresponding ratios for the fine soil are, in many cases, about 0.1 higher than above figures. 4. In major cases, the red-colored limestone-soils are nearly saturated with calcium, while in minor cases, the soils are unsaturated and the acidities increase with the depth of soil layer. The colloidal sillica : sesqnioxide ratios are 1.1〜1.4 in approximation. 5. As compared with the other limestone soils, the yellow-colored soils are more acid and less saturated. In many cases, their exchang acidity and hydrolytic acidity increase with the depth of soil profile. The degree of saturation for two subsoils was found to be approximately 70% The base-exchange capacity is relatively high. The colloidal silica : sesquioxide ratios are 1.3〜1.5. 6. The acidities of non-limestone soils vary, in general, according to the place of soil occurence. Thus, in some cases, the soils are quite neutral throughout the whole profile; while in other cases, they are more acid, and the acidities increase or decrease with the depth of soil layer. The former cases are found in places where lime is abundantly supplied from the neighbouring limestone for neutralization. The andesite soils occuring on the summit of the Rota mountain, are strongly acid, the acidities decreasing with the depth. The degree of base-saturation is only 9 per cent for the subsoils. The silica : sesquioxide ratios for andesite soils vary with the place of occurence. The soils from tertiary rocks excluding limestone, have high base-exchange capacity. The degree of saturation is about 60 per cent. The colloidal silica : sesquioxide ratios are 2〜3. 7. The contents of phosphoric acid and potash, that are soluble in 0.2 n HCl, also vary with the locality of soil. However, in major cases, the contents are higher in surface soils than are in subsoils. Averaging the amounts, obtained with 29 surface soils and 21 subsoils from various limestonesoils, the following figures were found as mean values for the two nutrients.[table]As will be seen, the quantitses of potash are markedly low, indicating its general lacking for limestone-soils. The field experiments also prove this fact. 8. The soils that were normally formed before reclamation from volcanic rocks and tertiary rocks, including old and impure limestones, under the dense forestcondition, would be assumed to be the yellow-colored soils. The soil-forming process then prevailed, should have been weak podsolization. The red-colored soils seem to be products of partial oxidation and weak laterization from the yellow-colored soils. The brown-colored soils from soft and coarse-structured limestone, also seem to have been normally developed under the cover of dense forest. But in this case, the supply of lime should have been large enough for neutralizing the humus produced. 9. In external appearance, the red-colored limestone soils resemble Terra Rossa; but they differ in that the soils are allitic in composition, although they have no evidence of being laterite. The brown-colored limestone-soils resemble

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