On the basis of the schema presented in the preceding paper that the soil humus consists of many parts continuously differing in "the lowest extraction pH", a method for characterizing humus composition among soils was devised. In the method, all the humus in a soil is considered a mixture of four humus fractions : Fr. I (acid-extractable), Fr, II (acid-inextractable, but neutral-extractable), Fr. III (neutral-inextractable, but alkali-extractable), and Fr. IV (alkali-inextractable). For determining the fractions, separate soil samples are extracted with three extractants, pH 1.2, 7.0, and 13, each containing pyrophosphate ion, for 48 hours at room temperature. The extracts obtained are subjected to carbon determination by a permanganate oxidation method. The content, in dry soil, of C in the form of Fr. I is calculated directly from the content of acid-extractable C, and those of Fr.'s II, III, and IV are calculated by the difference between the contents of acid-, neutral-, and alkali-extractable C, and total organic C (CA, CN, CAL, and CT, respectively). Fr. I is divided into two subfractions unadsorbable and adsorbable onto active carbon from acid solution (Fr.'s I-1 and I-2, respectively), and Fr. I-2 is divided further into two, elutable and unelutable with alkali from the active carbon (Fr.'s I-3 and I-4, respectively). Content of C in the forms of these subfractions is obtained from the determination of C in Fr. I, Fr. 1-1, and Fr. 1-3. On Fr. 1-3, its absorbance is measured at the wavelength of 270 nm with 0.1N NaOH as the solvent ; absorbance of the solution with a fixed concentration is represented by K270. From the analysis of 34 soil samples belonging to nine soil groups by this method, it was found that most of fractional C contents, ratios among them, and optical values of Fr. 1-3 were correlated to each other, CT, and soil pH also, and among them C_N, (C_T-C_N)/C_N, and K270 of Fr. 1-3 were the best values about the above correlation. PQ and optical values of alkali-extracted humic acid, however, had no correlation with soil pH. Most of the soil groups examined could be well separated from each other by plotting soils with the values of C_N and K270 of Fr. I-3. Result of a experiment in which a quantity of Japanese pampas grass straw was mixed into a soil and whose humus composition was analysed at intervals during 1.5 years by this method showed that small change in humus composition is possible to be caught by this method.

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We studied the chemical and mineralogical properties and genesis of a wet humus podzolic soil formed from volcanic ash in Hachimantai region of Iwate prefecture, Japan. Mineralogical study on the parent material indicated that this soil was formed from three tephra depositions ; rhyolitic Akita yakeyame pumiceous ash (AYP, A. D. 800 years) in the upper part, and felsic or intermediate ash depositions in the middle and lower parts of the profiles. According to the field observation, the horizons of this wet humus podozolic soil were described as follows ; F, HA, A, B, IIA, IIB_1, IIB_2 and IIB_3. However, based on the data of primary mineral composition and chemical analyses such as DCB, sodium pyrophsphate and humus composition of soil sample, the horizon sequence of this soil was finally determined to be F, HA, B_1, IIB_<21>, IIIB_<22>, IIIB_<23> and IIIB_3. All the soil samples had the very low base saturation degree and the very strong acidity. The value of pH (NaF) and phosphate absorption coefficient were very high in B horizons reflecting the remakable accumlation of amorphous Al and Fe. The ratio of the content of the humic acid to the content of humic acid + fulvic acid (PQ value) was greater in HA and H horizons and smaller in B horizons. The clay fractions were dominated by smectite in HA and A horizons and were mainly composed of 2 : 1-2 : 1 : 1 clay minerals intergrade and DCB solble Al and Fe in B_1, IIB_<21> and IIIB_<22> horizons. The IIIB_<22> and IIIB_3 horizons had the clay mineralogical composition of 2 : 1-2 : 1 : 1 clay minerals intergrade, halloysite, allophane, imogolite and DCB solble Al and Fe. DCB solble Al is wholly complexed with humus except IIIB_3 horizon, but DCB soluble Fe complexed with humus is about half in all the horizons.

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In order to elucidate the genesis of the so-called "non-volcanic" kuroboku soil in the Tokai district, Japan, forest soils in the north-eastern part of Aichi prefecture were analyzed on the content and the refractive index of volcanic glass as well as the chemical properties related to the volcanic origin. The samples included 3 acid brown forest soils as well as 4 koroboku soils. (1) All of the soils contained more or less volcanic glasses. According to their refractive indices, the volcanic glasses were inferred as originating from Aira-Tn and/or Akahoya ashes. (2) The carbon contents of the A horizons were 6〜19% and did not differ between the kuroboku and the brown forest soils. The C to N ratios of A horizons, however, were larger than 20 in the kuroboku soils and less than 20 the brown forest soils. (3) All the samples were strongly acidic, that is, pH (H_2O)&le;5.0, pH (KCl)&;e;4.1 and the exchange acidity Vj ranging from 9 to 65. (4) Phosphate absorption coefficients were 1300〜1900 in the kuroboku soils, and on the other hand 7 out of 14 brown forest soils samples had the value more than 1300. (5) Exept for one brown forest soil profile, all the soil profiles contained one or more horizons of pH(NaF)&ge;9.4. (6) Allophane test using KF solution and phenolphtalein paper showed the clearly positive reaction on 2 kuroboku and 2 brown forest soils. (7) Humic acids of A type were recognized in the A horizons of all the kuroboku soils as well as in a buried humic horizon and a B horizon of the brown forest soils. (8) Based on the results obtained above, it was considered that, the kuroboku soils developed at first after the falls of wide-spread ashes and then they were eroded, subsequently the brown forestsoils were formed, though some parts were protected from erosion and reworked areas remained as kuroboku soils.

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The soils formed from volcanic origin which are widely distributed in Japan, are one of the important arable soils in the country. The soils have been called as different names such as Volcanic Ash soils, Ando soils, Andosols, Kuroboku soils, Humic Allophane soils, Humified Allophanitic soils, Black soils recognized as an independent genetic soil type. The parent materials of kuroboku soils are originally from volcanic mateiials, however, all the soils from volcanic origin are not grouped into the Kuroboku soils. It is a basic principle that the kuroboku soils should not be classified only based on the parent materials, but on the soil characteristics. The most important features to be Kuroboku soils are that the soils are dominated by amorphous materials including allophane and allophane-like silicate minerals of alminium in the clay fraction. Amorphous materials in higher amounts reflect to the physico-chemical properties of the Kuroboku soils. At first, the bulk density of Kuroboku soils is lower than 0.9g/cm^3, exept for coarse textured Regosolic Kuroboku soils. Secondly, there are two types in dispersibility of Kuroboku clay : one is dispersible in a medium of hydrochloric acid, and the other is dispersible in a medium of hexamethaphosphate. The former is called as Typical Kuroboku soils, and the latter is Para-Kuroboku soils. The amounts of amorphous material of Typical Kuroboku soils are more than 20 to 30 percent, highr than those of Para-Kuroboku soils. The forms of alminium in Kuroboku soils are basic hydroxyl alminium at the pH between 7 and 4 where diverts from Al(OH)^+_2 to Al(OH)^<+2> according to the pH values of the bulk solution. Basic hydroxyl alminium is not exchangeable on the site of pH-dependent charge, resulting in low exchange acidity and low exchangeable aluminium contents for Typical Kuroboku soils. Trivalent alminium, stable in the pH lower than around 3.8, prevents clay dispersion, because the concentration of trivalent aluminium in the solution increases by the dissolution of aluminium from soil perticles. The values of exchange acidity and exchangeable aluminium of Para-Kuroboku soils are higher than those of Typical Kuroboku soils. It can be suggested that Alludands may be included in the Para-Kuroboku soils which are of low phosphate retention and low amorphous material contents. Typical Kuroboku soils have phosphate retention values (Blakemore method) of higher than 85 percent, and phosphate absorption capacity of higher than 3,500 mg P_2O_5 per 100 g soil. On the other hand, Para-Kuroboku soils have phosphate absorption capacity of 2,000 to 3,500 mg P_2O_5 per 100 g soils. It means that Para-Kuroboku soils are excluded from Andisols. The high humic horizons are denned as the horizons having more than 13 percent of organic carbon, and show a color value of 1.7 or less and a chroma of 1 in the field. The horizons are different from the melanic horizons in Andisols. According to these differentiation criteria, Kuroboku soils are classified into seven soil groups : Typical Kuroboku soils, Para-Kuroboku soils, Regosolic Kuroboku soils, Wet Kuroboku soils, Wet Para-Kurobok soils, Wet Regosolic Kuroboku soils and Kuroboku Gley soils. Typical Kuroboku soils have five subgroups : Thick High-humic, High-Humic, Thick Humic, Humic and Light-colored. The subgroups are subdivided into Active Aluminous, Allophanic, and Crystallitic, depending upon the composition of clay fraction. Para-Kuroboku soils, consist of two soils, Redeposited Ccrystallitic and Wind-blown Crystalliitc at a soil family level. Regosolic Kuroboku soils are defined as the soils which have more than 2.9 percent organic carbon (5 percent organic matter) in a weighted average of 25 cm from the surface, 2,000 mg P_2O_5 or less of phosphate absorption capacity and less than 10 percent of clay.

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The area studied for transmigration settlement development in Muara Rupit, South Sumatra, Indonesia, mostly lies on dissected uplifted plain with rounded ridges and is covered by forest vegetation. Geologically, this area is mainly underlain by claystone, sandstone and andesite. Climate is tropical, as annual precipitation averages about 3,100mm and mean monthly temperature is more than 25℃ throughout the year. The soil may be differentiated into 5 groups, 8 types and 17 sub-types. This classification and grouping follows the result of soil examintion by auger boring and profile pits, based on a grid pattern. In the uplifted plain it is natural that Red-yellow soils predominate. These soils which may be divided into two groups (Group C and Group A) are mainly deep and clayey and have gradual horizon boundary, relativsry uniform profile, a thin A-horizon and a poorly developed layer of litter. Soils of Group C which are mainly found on gentle slopes and foot slopes in the uplifted plain have an indistinct accumulation of clay and subsoil with some mottles. These soils may be correlated with Dystric Cambisols of FAO-UNESCO (FAO) and/or Dystropepts of USDA Soil Taxonomy (ST). Soils of Group A, which are mainly found on sloping area have illuviated B-horizon and may be correlated with Dystric Acrisols of FAO or Tropudults of ST. Group A may be divided into two types, Type p^3 and Type p^4 in relation to soil development. The soils of p^3 have a marked illuviated B-horizon and a brown subsoil. The soils of p^4 are similar to those of p^3, except that they have a moderately illuviated B-horizon and a redder subsoil. The soils on flat plains at low elevation, mainly occurring along rivers, show hydromorphic properties and can be correlated with Dystric Fluvisols or Gleyic Fluvisoils of FAO and/or Tropofluvents of ST. These soils are usually moderately acid association with low base saturation and low exchangeable cations. Their phosphorus and nitrogen content minimal. The difference between Group C and Group A might result from their drainage condition in association with micro-topography.

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[in Japanese]

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