Pedologist

The morphology and physicochemical properties of soils in Kratie, central Cambodia, were studied to characterize the forest soils in relation to the presence of plinthite and to elucidate the soil physicochemical factors affecting the distribution of dry deciduous forests in seasonally dry tropics. Plinthic soils (sites NT-1 and NT-2) differed from non-plinthic soils (sites SE-1 and SE-2) in the presence of a Bv horizon that contained hard and rounded iron nodules and a sand fraction with a more red color and rounded shape. Despite the difference in soil morphology, the effective soil depths of all four plots, as estimated by soil hardness, were remarkably shallower (<70cm) than the evergreen forest soils on the west bank of the Mekong River. The difference in effective soil depth between the two regions is thought to control the large-scale distribution of the evergreen and deciduous forests in central Cambodia. The soils in the study area showed high pH, high exchangeable base content, and high CEC/clay values. According to the WRB classification, soils in NT-1, NT-2, SE-1, and SE-2 were classified as Pisoplinthic Lixic Plinthosols, Pisoplinthic Lixic Plinthosols (Albic), Albic Alisols (Ferric, Clayic), and Albic Luvisols (Hypereutric, Profondic), respectively. According to the US Soil Taxonomy, the soils were classified as Plinthic Paleustalfs (NT-1 and NT-2), Ombroaquic Haplustults (SE-1), and Oxyaquic Haplustalfs (SE-2).

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Physico-chemical comparison between argic horizons and cambic horizons of Red and Yellow soils had not been conducted at nationwide scale in Japan. Therefore, characteristics of argic horizon had not been well defined in Japanese soil taxonomy system. To locate the taxonomical position of argc horizon in Japanese system, we elucidated the physico-chemical differences between argic and cambic horizons using database analysis. Additionally, we assessed the validity of soil colors criterion i.e. "Red" and "Yellow" in the diagnostic criteria of Japanese system. Silt to clay ratio and cation exchange capacity (1kg clay base) of argic horizons was significantly lower than those of cambic horizons. Furthermore, it appeared that argic horizons developed on the stable landscape while cambic horizons developed on the mountain or hill ranges. These results indicated that development of agric horizons requires long pedogenetical time and landscape stability, and it is thought to be an indicator of soil weathering in Japan. Additionally, database analysis revailed that a diagnostic criterion which is solely based on the soil color was not a valid criterion in the high category of soil classification system. However, after distinguishing higher category using the presence of argic or cambic horizons, soil color was useful as the diagnostics criterion of lower category. Therefore, we recommended that higher categories (soil groups) of Red and Yellow soils are distinguished by the presence of argic or cambic horizons, and lower categories of those are identified from the soil colors.

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In Qinghai-Tibet Plateau, the most productive and important grasslands are Alpine meadows which occupy about 50% of available alpine rangelands. The characteristics, types, and spatial patterns of Alpine meadow soils were investigated in Menyuan Valley in Qiliag Mountains where is the main distribution place of Alpine meadow. Haplic Phaeozem (Calcaric, Pachic, Siltic), Haplic Cambisol (Calcaric, Humic, Siltic) and Haplic Stagnosol (Calcaric, Humic, Siltic) were formed on the terrace of alluvial fan, Haplic Fluvisol (Calcaric, Humic, Episkeletic) on the old river channel of alluvial fan, and Haplic Fluvisol (Calcaric, Humic, Endoskeletic) and Mollic Fluvisol (Calcaric, Humic, Endoskeletic) on the channel bar of alluvial fan. Moreover, Haplic Fluvisol (Calcaric, Humic, Endoskeletic, Siltic) was formed on the old river channel of valley plain, and Haplic Fluvisol (Calcaric, Humic, Siltic) and Gleyic Fluvisol (Calcaric, Humic, Siltic) on the channel bar of valley plain. The Alpine meadow soils in Qinghai-Tibet Plateau include at least four reference soil groups and their nine second-level units of the WRB formed corresponding to different micro-landforms in alluvial fan and valley plain. The Alpine meadow soils are one of the most fertile soils that have almost no problem in physiochemical properties as grazing soils except the episkeletic soils and have the highest organic matter contents in the mineral soils of the world. However, the Alpine meadow soils are highly susceptible to wind erosion. If degradation of grasslands takes place, there is a possibility of causing serious erosion.

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