Monday, 10 July 2006

Topo- and Bio-Sequence of the Soils in the Fukiage Coastal Dune.

Tadao Hamazaki and Taiki Kusahara. Faculty of Agriculture, Kagoshima Univ, 1-21-24 Korimoto, Kagoshima, Japan

Soils of a coastal dune are immature and these soils are generally included in the taxonomic unit Sand-dune Regosols in Japan. Hence, research on these soils from the perspective of soil genesis is seldom undertaken. A sand dune deposit on the other hand, is a coarse and permeable parent material. Podzolization can easily take place in such parent material regardless of the climatic zone if it is under a coniferous forest where the development of organic horizons is favorable. The characteristics, genesis, and classification of soils, which change with micro-topography and vegetation as observed between the old and new sand hills in the Fukiage coastal dune of South Kyushu (with warm temperate climate) were investigated. The Fukiage coastal dune is one of the three major coastal dunes in Japan, and it is a sand dune with a length from north to south of 47 km and a width of maximum 2.5 km. This coastal dune has two distinct sand hills, with the front sand hill located towards seashore and the back sand hill located inland. A marsh and three steps of sand benches are found between the two sand hills. Eight pedons (FK1~FK8) along a 1.6 km transect that cuts across the two sand hills with different micro-topography and vegetation were selected. The selected sites are located in Kinpo area of Hioki City, Kagoshima Prefecture, which is in the center of the Fukiage coastal dune. Main results of the investigation are as follows: 1) The micro-topography from the seashore to the inland consists of a front sand hill and a marsh in its back, continuous three steps of sand benches, and a back sand hill. 2) Corresponding to micro-topography, the vegetation changes in order of non-vegetation (FK1), Hibiscus hamabo community (FK2) and Pinus thunbergii forest accompanied by Japanese pampas grass (FK3) in the front sand hill, Andropogun virginicus grassland (FK4) in the marsh, Pinus thunbergii forest (FK5~FK7) accompanied by Hypnum plumaeforme in the three steps of sand benches and evergreen broad-leaved (Quercus glauca) forest (FK8) in the back sand hill. 3) Many pieces of shells and weakly developed A horizons were observed in FK1 and FK2, while FK3 has a well developed A horizon. The groundwater level in FK4 was less than 1m in depth and iron mottlings were observed in every horizon. In FK5-FK7, organic horizons of L/moss/F, bleached horizons, and iron accumulation horizons were developed. In FK8, distinct A horizon was developed below a thin L/F horizon. 4) The solid phase ratios of soils ranged from 20% to 55%, with values increasing in subsoils in the inland. The liquid phase ratios of FK4 were much higher than those of the other soils. 5) The values of pH were higher in FK1 and FK2 than in inland soils. Values of pH decreased toward the surface except for FK2 and FK3. The exchange acidity was 0 in FK1 and FK2; but high values were observed in the inland soils with a tendency to increase toward the surface. 6) The organic matter content was high in FK6, FK7 and FK8, and slightly high also in FK3. 7) Values of CEC had the same tendency as the organic matter content, which indicates the influence of organic matter content on CEC. The soil horizons of FK1, FK2, and the bottom of other soils were saturated with bases. FK6 had the lowest pH and base saturation percentage but highest exchange acidity and organic matter content, and had the most pronounced morphological iron accumulation. 8) Based on these results, the soils developed under the topo- and bio-sequence of the Fukiage coastal dune were classified into Proti-Calcaric Alenosol (FK1), Calcaric Alenosol (FK2), Hypereutric Alenosol (FK3), Hypereutri-Endogleyic Alenosol (FK4), Endoeutri-Albic Alenosol (FK5) Epidystri-Albic Alenosol (FK6), Endoeutri-Albic Alenosol (FK7) and Endoeutric Alenosol (FK8) according to World Reference Base for soil resources.

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