Pedologist

For paddy rice, the relationships between soil conditions (fundamental properties and depth of plow layer) and altitude difference (relative elevation), and cool summer damage were systematically analyzed, and the following results were obtained. 1) As factors which affected cool summer damage of paddy rice, soil types, depth of plow layer, active aluminum reaction of the plow layer, and relative elevation were extracted. 2) In the soil types such as medium, coarse or gravel soils having excessively well permeability and low nutrient holding capacity, and fine soils having very poor permeability and very strong reducibility, paddy rice is most easy to receive cool summer damage. And in the soil types having moderately poor permeability, not very strong reducibility, and high nutrient holding capacity, paddy rice is most difficult to receive cool summer damage. 3) Paddy rice is difficult to receive cool summer damage, as plow layer is deeper. 4) Paddy rice is easy to receive cool summer damage, as active aluminum reaction of plow layer is stronger. 5) Relative elevation occurs the difference in 33m in the susceptibility of cool summer damage of paddy rice. It is shown that soils can be improved in these difficult to receive cool summer damage by land improvement and soil management.

View full abstract

This study offered an example to investigate the process of introducing living organisms into inorganic parent materials or to establish soil ecosystem. This process was also considered to be the initial stage of soil formation. The well-developed and characteristic habitat of Bryophyllum Tubiflorum as a pioneer plant was observed on the thin volcanic ash layer which deposited within these ten years. The well development of the habitat was needed to be enough and continuous supply of nutrients. Nitrogen is one of the most important elements for plant growth. But original ash contained very small amount of nitrogen source. Therefore, it was suggested that large numbers of micro-organisms inhabited in the ash layer before the appearance of higher plant growth on the layer and the decomposed nitrogen from the organisms were ensured the plant growth, i.e. The essential nutrient for the growth of the plant except N, were provided in original volcanic ash as watersoluble ions. The cationic ions of them were changing to exchangeable forms as the advancing of the vegetative succession accompanying the weathering of volcanic ashes. This finding means that the surfaces of the particles of the ash layer were becoming gradually to be negatively charged ones capable to retain cations though soil formation was yet in very young stage.

View full abstract

The potential acid sulfate soil formation from central Kyushu, Japan was studied using stable isotope technique. Subsurface soil horizons developed from fluvio-marine sediments around Chikugo river estuary and from peaty sediments within Aso Caldera contain significant amounts of sulfide-sulfur of which a part is easily oxidized to form active acid sulfate soils (pH: around 3 in water suspension) upon aerial oxidation. Sulfur isotope composition (^<34>S/^<32>S ratios, commonly designated as δ^<34>S) of air-dried materials for water-soluble sulfate-sulfur and sulfide-sulfur fractions oxidizable with warm hydrogen peroxide showed distinct δ^<34>S values ranging from -32.0 to +8.1‰ which are lighter than those of seawater-sulfate (Chikugo river estuary; δ^<34>S=+21‰), local groundwater (within Aso Caldera; δ^<34>S=-2.3 to +23‰), fresh volcanic ash (δ^<34>S=+3.0‰), and hot spring (δ^<34>S=+0.8 and +2.0‰) sulfates. Sulfate-reducing bacteria are responsible for formation of active sulfide with such low δ^<34>S values. Sulfides which are easily oxidized into sulfuric acid upon air-drying tend to be depleted with heavy sulfur (^<34>S), relative to unoxidized sulfides and elemental sulfur.

View full abstract

Show abstractHide abstract

The total carbon / total nitrogen (C/N) ratio of organic materials, the particle size distribution and the clay mineral composition of the soil horizons which had been sedimented in the bottoms of Lagoons Nisinoko and Syounakanoko during the last 18,000 years were examined by a CN corder method, a laser scattering method, a X-ray diffraction method and thermal analyses. The analytical data were discussed by relating with the changes of past climates. The results are summarized as follows: The C/N ratio of soil horizons formed in the terms of warm climates were lower than that of the cool time. It is suggested that the decomposition rate of organic materials had been accelerated under the condition of relatively high temperature, accordingly. The particle sizes of the horizons corresponded to the terms of cool climates were coarse compared with the warm terms, in the shallow lagoons such as Nishinoko and Shounakanoko. The coarse textures of these horizons should be caused by the following reason, i.e., the lagoons shifted relatively to the part of upper stream in proportion to the decrease of water level in the lake and the lagoons as the decreased of precipitation during the cool term. On the other hand, the lagoons were filled by water in the warm term as the increase of precipitation, and the soil texture became fine in the corresponding horizon. The contents of kaolin minerals are high relatively in the horizons associated with the terms of warm climates, while mica minerals and smectite were rich in the cool terms. It is generally said that the genesis of kaolin minerals is accelerated under the condition of hot or warm climate. The lower soil-horizons were abundant in chlorite compared with upper ones, which suggested an influence of diagenesis. Amorphous materials were especially high in the clay fractions from the horizon of B.P. 6,000, which should be influenced by "Akahoya", the tephra from Kikai Caldera.

View full abstract

Download PDF (712K)

Register with J-STAGE for free!