Properties of volcanic soil in Thailand and Japan

Since 1978, the new soil order called Andisols that developed in volcanic materials have been revised and defined in Soil Taxonomy, many soil maps and classification units of the world have been affected by acceptance of this order. The soils formed from volcanic materials in Thailand (the Tha Mai and the Chok Chai soil series) were, studied in detial to determine whether or not they were Andisols. The field morphological characteristics, physical, chemical and mineralogical properties of these soils were determined following the standard method for soil classification. The results were then compared with the colcanic soil in Japan (Typic Melanudands). The data of this study showed that the Tha Mai soil series was classified as Typic Haplorthoxs; clayey, kaolinitic; isohyperthermic, while the Chok Chai soil series was classified to be Typic Haplustoxs; clayey, kaolinitic; isohypertermic. Both these soils have thick oxic horzon which indicates very well soil profile development of Oxisols soil order. The leaching and weathering processes are very active because the areas are located in the tropical climate. This results in the presen of clayey texture, which is dominant in kalinite and oxide minerals. The reddish colour and granular structure in the soil are reflected of those oxide clays. The soils have low to medium exchangeable cations (sum cations Ca, Mg, K and Na of 0.6-5.3 cmol/kg), moderately low cation exchangeable capacity (CEC of 8.6-10.7 cmol/kg), and very low to medium organic matter contents (OM of 0.2-2.1 g/kg). The Andisols in Japan (Typic Melanudands; fine, loamy, mixed; mesic) has very high organic matter contents (OM of 8.1-12.3 g/kg) from the surface soil extending to the depth of 115 cm and high cation exchangeable capacity (CEC of 17.0-25.7 cmol/kg). This is because of the slowly weathering and active melanization processes in low temperature under pasture fields of warm temperate zone. Even though the soil is formed from the same volcanic materials, the degree of weathering process is believed to be the major factor imparting differences in soil morphology, and of physical, chemical and mineralogical properties of volcanic soil between Thailand and Japan.