Pedologist

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Four soils (Meadow Black soil, Ortho Black soil, Chernozem, and Steppe Solonetz) in Jilin, China, were used. The soil was saturated with sodium ions, sonicated in water suspension, and separated into various size organomineral complexes by successive sedimentation and centrifugation; fine clay (<0.2μm), coarse clay (0.2-2.0μm), silt (2-20μm), and fine sand (20-200μm) size separate. Humic acid (HA) was extracted with acidified DMSO solvent from these separates and analyzed on E_<600> (absorbance coefficient of 1% HA solution at 600nm), elemental and functional groups composition, component distribution separated with XAD-8 resin, and hexose, pentose, amino-N, and lignin contents. The content of organo-mineral complex decreased with lowering their particle size. The carbon enrichment ratio (gC kg^<-1> separate to gC kg^<-1> whole soil) was high in coarse clay size separate of four soils and was also high in silt size separate of Chernozem and Solonetz. The C/N ratio of organic matter in size separate declined with decreasing particle size. The E_<600> value of HA decreased in the order: coarse clay > silt >> fine clay and fine sand size separate. From the atomic H/C versus O/C diagram, the HAs of coarse clay and silt size separate would be highly subject to dehydration and demethanation in comparison with the HAs of fine clay and fine sand size separate. Carboxyl and phenolic hydroxyl group content and carboxylic component ratio of the HAs in coarse clay and silt size separate were higher than those of the HAs in fine clay and fine sand size separate. Alcoholic hydroxyl group content and aliphatic component ratio and hexose, pentose, and lignin content in HAs of the former separate were lower than those of the latter separate. The principal component analysis by the characteristics of HA (8 variables) clarified the two factors highly correlated with quantitative and qualitative characters of HA separately. The groups of the organo-mineral complex divided by the cluster analysis, using principal component score, showed clearly the differences between the two soil groups and the two particle size separate groups.

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Land consolidation on Neogene sedimentary rocks often results in strong acid sulfate weathering which constraints subsequent land uses. Sulfur isotopic composition of the sulfide and associated sulfate minerals from marine sediments along the Kitakami River Basin, northeast Japan was studied. Large sulfur isotopic fractionation between sulfide minerals and concomitant seawater sulfate was observed for marine sediments formed under open oceanic conditions, relative to those from inland bay. Similarly, smaller sulfur isotopic fractionation was observed for sulfide minerals from deep sea sediments than those from shallower sea sediments. Very limited sulfur isotopic fractionation was observed for both brackish and terrestrial sediments. The sulfide minerals from Neogene sediments along the Kitakami River Basin reserve their sedimentary environments when the minerals were formed. There could not be found a definite relationship between the sulfur isotopic composition and the development of acid sulfates upon air drying of sediments.

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Upland soils were collected from 114 sites of southern and eastern part of Hokkaido, Japan and they were mostly Andosols. The water-extractable Al, a possible index of potato scab suppression, was determined and the factors affecting the water-extractable Al levels were discussed in this study. High Al concentration in the water extract, 0.3 mg L^<-1> or more, considered to be resistant to potato scab, were found at 23 sites including 14 plow layers. Although the water extractable Al was negatively correlated with soil pH values, soils with low to high levels of water-extractable Al were included in the region of 5 < pH (H_2O) < 6. The most important factors affecting the water-extractable Al levels of this pH region were organic carbon content and oxalate-extractable Si. The soils which showed high water-extractable Al level contained larger amount of organic carbon and smaller amount of oxalate-extractable Si than those with low water-extractable Al level. Humus may increase water-extractable Al, possibly buffering Al between solution and Al complexed with humus. Allophane and imogolite may decrease water-extractable Al by sorption of Al.

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We investigated the organic carbon content and phytolith in successive samples of a cumulative Andisols profile in Miyakonojo basin. In this study, the following results were obtained: 1) Organic carbon content was changed successively from lower to upper layer. This showed various changing patterns of organic carbon content, considered to have been based on the volume and condition of parent material deposition, climate, and thickness of the vegetation. 2) From phytolith analysis, different grass species were detected to be dominant in each horizon: Phragmites in 10Bt-8B2, Sasa (except Miyakozasa) in 8B2-8A2, Miscanthus in 8A2-7A/C2, and Pleioblastus sect (Medake and Nezasa) in 7A/C2-1Ap. This is considered to have changed a plant mainly composed of supply of soil organic matter with the change of the time. 3) Highly positive correlation was observed between total yield of grass vegetation estimated from phytolith analysis and organic carbon content in a cumulative Andisols at Oiwada, Miyakonojo. The gradient of each correlation curve was similar to the 5〜4 and 3〜2 horizons with buried humus layers. This suggested that the organic carbon contents of these horizons have not almost been decreased after buried with the upper tephras within thousands of years that have been passed.

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