CLASSIFICATION OF PODZOLIC SOILS AS AFFECTED BY CULTIVATION

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The effects on soil properties of long-term potato cultivation and of erosion were studied by sampling soils along three transects in virgin forest sites and seven transects in potato fields with landforms and parent materials similar to those of the forest sites. The average thickness of solum was reduced from 35 cm in virgin forest to 27 cm in cultivated fields. More than 90% (28 of 30) of forested pedons were classified as Podzolic soils but only 27% (19 of 70) of the cultivated pedons met all of the criteria of Podzolic soils. The others were mainly Regosols and Brunisols. The main criterion that excluded the soils from the Podzolic order was one of the morphological criteria which states "… hue of 10 YR near the upper boundary (of B horizon) and becomes yellower with depth." Most of the Ap horizons (70%) still meet all the chemical criteria for the Podzolic order. By waiving the morphological criterion stated above for the cultivated sites, nearly 70% (48 of 70) of the soils observed remained as Podzols with only a minor amount of Regosols and Brunisols. It is proposed that the current morphological criterion should be retained for uncultivated soils, but waived for cultivated soils. This will decrease the contrast between the classification of cultivated and adjacent forest soils. We also suggested that the morphological changes resulting from cultivation and erosion can be dealt with at a lower categorocal level or as a phase of categorical levels. Key words: Chemical criteria, morphological criteria, soil erosion, soil transect