Andisols of the Kitakami mountain range, northeastern Japan: Their characterization and classification

Andisols of the Kitakami mountain range were derived from a mixture of tephras and long range eolian dust deposited during the Quaternary. Thus, the relative proportions of the components of the mixture determined the unique properties of the soils. Soils of the northern and central parts of the mountain range were derived mainly from tephras and had been classified, generally, as Typic Kuroboku soils by the Group of Japanese Pedologists. Soils of the southern part showed a strong influence of long range eolian dust and had been classified, generally, as Typic Para Kuroboku soils. We studied the Andic soil properties of 35 pedons covering the mountain range in order to classify them under the Andisols order. All the soils showed a bulk density (BD) <0.90 Mg m(-3) and P retention >85% in the Andisol diagnostic horizon. The soils of the northern and central parts of the mountain range had a pH(H2O) range of 5.1-6.7 and acid oxalate-extractable Al plus half Fe (Al-o+0.5Fe(o)) level was >2%. They were therefore classified under criterion one of the Andic soils requirements. The soils of the southern part of the mountain range had a pH(H2O) range of 4.3-5.7 and the majority of them contained <2.0% of Al-o + 0.5Fe(o). The pedons with Al-o+0.5Fe(o) level <2.0%, however, had a sufficient amount of volcanic glass in their sand fraction to satisfy the criterion two of the Andic soil requirements. The soils of the northern part contained moderate amounts of organic C and were mainly Typic Hapludands. The soils of the southern part contained large amounts of KCl-extractable Al and organic C and also showed a wider spectrum of Andisols. However, Alic and Typic Fulvudands, and Alic and Typic Melanudands tended to occur in higher frequencies, The classification of the pedons of the central part bridged that of the pedons of the northern and the southern parts.