Free oxides properties of Japanese forest soils developed from volcanic ash and other parent materials.
Akihiro Imaya, Kyusyu research center, Forestry and Forest Products Research Institute, 4-11-16 Kurokami, Kumamoto, 860-0862, Japan, Seiichi Ohta, Kyoto University, Sakyo-ku Kitashirakawaoiwake-cho, Kyoto, 606-8502, Japan, Yoshiyuki Inagaki, Shikoku research center, Forestry and Forest Products Research Insitute, 2-915 Asakuranishimachi, Kochi, 780-8077, Japan, and Nagaharu Tanaka, Hokkaido research center, Forestry and Forest Products Research Institute, Hitsujigaoka-7 Toyohira-ku, Sapporo, 062-8516, Japan.
It is essential to understand the soil chemical properties for evaluation of the multiple functions of forest soils such as water and nutrients supplies to tree plants, carbon sequestration, conservation of stream water quality and so on, and also for prediction of the their change with environmental change. The chemical properties of forest soils are affected by climate, vegetation and parent material. Approximately 70 % of the forest soils in Japan consist of Brown Forest Soils (BFS) which were the zonal soils in the humid temperate and warm temperate. There were many similarities in the chemical properties between the BFS derived from volcanic ash and the Black Soils (BLS), and the differences between them were chiefly related to the morphological features and accompanying carbon content and bulk density. On the other hand, the BFS derived from non-volcanic ash and volcanic ash were similar in their morphological features but not in their chemical properties. The difference was larger than that between the BFS derived from volcanic ash and BLS. According to the classification of U.S. Soil Taxonomy and World Reference Base for Soil Resources, the BFS were divided into Andisols or Andosols from volcanic ash and Inceptisols or Umbrisols / Cambisols from non-volcanic-ash parent materials. In the present study, since the parent materials of the soils were evaluated from the surface geology. Point of view, it is possible that the soils derived from parent materials other than volcanic ash also contained some volcanic ash. Volcanic ash on the mountain slope does not remain as a volcanic ash layer due to erosion, and the degree of contamination with volcanic ash varied with the amounts of descent, terrain and other factors. Since volcanic ash strongly affects the chemical properties of the soils, the degree of contamination with volcanic ash might be estimated using the chemical properties of the soils as an index. Actually, BFS strongly influenced by volcanic ash were extracted by using the free oxide composition as an index. In this report, we will clarify the composition of free oxides in the BFS developed under various surface geological conditions, and examine the influence of volcanic ash on the soil characteristics. With regard to composition of free oxides the crystalline Fe dominated in the non-volcanic BFS, and organically complexed Fe and Al was detected in their surface horizons. While in the BFS derived from volcanic ash contents of allophane and imogolite increased with depth and became dominant in deeper horizons. Contrarily, amorphous Fe and non-crystalline Al-hydrous oxides dominated in the BLS. Organically complexed Al contents were correlated total carbon contents, except for those from limestone and serpentine. Soils from limestone and serpentine were indicated high pH values. This is because a high pH value decreases the stability of free Al oxides, and decreases organically complexed Al contents. However, organically complexed Fe contents were different the relation to the content of the carbon though the relation to the pH was similar to aluminum. The contents of organically complexed Fe to the contents of total carbon were low in the volcanic ash soils. The contents of sodium dithionite-citrate extract Fe were related to the contents of clay. The contents of acid oxalate extract Fe were provided for by the contents of sodium dhitionite-citrate Fe and mean annual temperature. It was greatly different the contents of acid oxalate extract Al were whether the parent material was volcanic ash. In volcanic ash soils, the contents of acid oxalate Al increased with the increase in contents of clay and delta pH value. Thus, the climates controlled as for the value of free iron oxides and volcanic ash influensed to the value of free aluminum oxides.