Tan Cuong commune in Thai Nguyen province is praised for the best tea quality among the northern region of Vietnam. In the commune, the market price of tea leaves was high at the gardens close to the Cong River and tended to lower with increasing distance from the river. In this context, soil morphological, mineralogical and chemical properties were investigated to characterize the soils in four tea gardens which were located on a transect line established perpendicularly to the river: TB1 close to the river, TB2 to TB4 away from the river and located on the previous dikes. The investigation was also conducted at two forested patches (FB1 and FB3) adjacent to TB1 and TB3. In addition, one garden was selected in Song Cau commune (TS1), located on a hillslope. All of the tea garden soils were strongly acidic throughout the profile with high contents of exchangeable Al. At the riverside, the TB1 and FB1 soils were classified as Typic Ustipsaments. They were sandy and predominated by quartz and kaolin minerals in the clay fraction. Meanwhile, the TB2 to TB4 and FB3 soils far from the river were Typic Dystrusteps while the TS1 soil was Typic Paleustults. These soils were relatively fine textured with various kinds of 2:1 clay minerals. The (Fe_d-Fe_o)/Fe_t ratio was the lowest in TB1 and FB1 and the highest in TS1. The analysis of total element contents agreed with the difference in these mineralogical properties. In addition, the influence of soil disturbance was found in TB2 and TB4. While the former was weakly reflected only by discontinuity of the horizon stratification and mineralogical properties, the latter was so severe resulting in a very shallow soil depth with abundant rock fragments.

北海道十勝地域において，ナガイモ栽培の深耕に伴う土壌撹乱が土壌断面形態に及ぼす影響を調べるとともに，撹乱された土壌の分類について検討した。1986年から現在までにナガイモ栽培を6回行った生産者圃場において，比高の高い地点（上部）と低い地点（下部）の2地点で土壌断面調査を行った。各地点において，バックホーを用いて作業方向に対して垂直な方向に約5 m掘削し，深耕による撹乱の影響を受けている部分と受けていない部分が同時に観察できる地点を選定した。未撹乱部分は層位ごと，撹乱部分は深さごとに土壌試料を採取し，粒径組成，理化学性および選択溶解法によるAl，FeおよびSi量を分析した。上部と下部のいずれの地点でも，深耕や掘削による土壌撹乱を受けていない部分は，掘削した約5 mの中で20-40 cm程度しかなく，大部分が撹乱されていた。撹乱後の部分は層位区分が明確ではなく，撹乱前の部分を見つけることができなければ断面記載を行うことも難しい。本調査では，未撹乱部分を見つけることができたため，その記載と理化学性などに基づいて腐植質褐色アロフェン質黒ボク土（混層造成相）に分類することができた。しかし，撹乱部分は表層土と下層土が混和されることにより土色や理化学性が均質化されているために亜群レベルでの判定が困難になることが予想される。さらに下層に低地土や台地土などが混入する場合には黒ボク土大群に分類されなくなる可能性がある。