Japanese Journal of Soil Science and Plant Nutrition

There is a considerable amount of Pele's tears in the fine sand fraction (0.2〜0.02mm) of the Japanese volcanic ash soils. Their appearance, optical properties, and contents in the various horizons of the subtypes with special reference to the origins of the ash soils have been described in the present paper. 1. The appearance of Pele's tears is rectangular, belonitic, or claw-shaped stone-like. Although many minute, shallow pores can be seen on the surface, Pele's tears cannot be considered to be porous as pumices, and some of them have been coated with a thin film of brown iron oxide. Usually they are 0.05〜0.10mm in length or in diameter, and are colorless, but in reflected light cloudy. Between crossed nicols they are isotropic, and their refractive index is very low, about 1.450. 2. The fact that the A horizon of Onji type(glassy, pyroxene-andesitic ash soils, Kirishima origin?) is characterized by a large quantity of Pele's tears offers a marked contrast to the small contents of the other subtypes, especially to those of Yellowish brown type(pyroxene-andesitic ash soils, Aso origin). Consequently, Pele's tear content may be regarded as an important criterion of identifying the black A horizon of Onji type (Kuro-0nji).

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Nitrificatins in Yellow and Ando soils were studied this time. Nitrifications of ammonium sulphate in these soils were poor. The nitrifications were, not be iufluenced by the applications of phosphorus or potassium, but they were somewhat obviously affected by the use of calcium oxide to correct soil acidity and by the inoculation. Chemical oxidation of N0_2 to N0_3 was here proved to take place when NaN0_2 was added to these acid soils, but microbiological oxidation took place mainly in the nitrification when ammonium salt was applied. Poor nitrification of these soils was due to feeble nitrifing bacteria (nitrosomonas and nitrobacter) and also to the acid reaction.

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Soil survey was made in Kanaya-cho by the pedological idea. The Soil types, prevailing in the arable land of this area numbered eight as follows. I. Zonal soil types (Vegetation soil types) Brown forest soils; Prairie-like brown forest soils. II. Azonal soil types (Mountain soil types) Mountain soils; Colluvial soils III. Intrazonal soil types (Ground water soil types) Meadow soils; Meadow soil, river-bed types, Gray lowland soils; Brown lowland soils These eight soil types were classified into soil kinds, 35 in total, after their minor morphological characters. Basing on the results of the soil survey, map of soil types, Kanaya-cho was made.

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The authors studied the soil-forming process of the halogenetic polder soils developed along the seacoast of the inner Kojima Bay and investigated the distribution of soil types and the characteristics of these soils. As polder soils of Kojima Bay have been developed under the influence of alkali salts, we grouped these soils as halogenetic soils. After being diked, it was found that polder soils were subjected to process of desalinization and solotization. The greater part of polder soils recently diked belongs to the younger halogenetic polder soils. These soils contain a large amount of the soluble salts of sea water and of the exchangeable bases, among which Mg and Na are more prominent. The base-exchange complex is nearly saturated with bases and the hydrolytic acidity is very small. Hence the reactions of these soils are neutral or slightly alkaline. These soils show the characteristics of the saline alkali soils of DE'SIGMOND. Younger acid halogenetic polder soils are found on poorly drained region along the dike. Air-dried surface soils show extremely strong acidities, ranging from pH 3 to pH 4,under the influence of iron sulfides formed under an anaerobic condition. Soluble salt content is also much, especially sulfates constitute the dominant salt among the salts. The V values are very low. Slightly leached halogenetic polder soils are found close to the non-leached soils above mentioned. When a part of the sodium salt have been washed out from the upper soils by the rain or irrigation water, the salt content of the surface soils is decreased but that of subsoils is 0.1 per cent or more as Cl. The exchangeable mono-valent cation (Na and K) decreases slightly in surface soils but remains unchanged in subsoils. The pH values of surface soils are 6〜7,and those of subsoils, 7 or more. Moderately leached halogetic polder soils distribute in the greater part of Fujita-Son and in a part of Kojo-Son and Nadasaki-Cho, which had been embanked from 1820 to 1900. Soluble chloride content of the surface soils is below 0.04 per cent. The pH values of surface soils, are 5.5-6.0,and those of subsoils, 7 or more. The hydrolytic acidity of the surface soils increases to as much as 20 or more. Strongly leached halogenetic polder soils distribute in the background, which had been diked from 1610-1820. With a continued supply of non-saline water, the leaching process advances greatly and the salts of all horizons are thoroughly washed out. Hence the solube chloride content of all horizons is below 0.04 per cent. Of exchangeable bases, Na and Mg are replaced by hydrogen and V values decrease greatly. The pH values of surface soils are 5.0-5.5,and those of subsoils, below 7. These ultimate products of leaching process, named strongly leached halogenetic polder soils, show the characteristics of the degraded alkali soils of DE'SIGMOND. A close relationship is found between the date of enclosure and the distribution of each soil types in this region.

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