1996 年 40 巻 1 号 p. 41-52
In Northeast Thailand, the soil degradation is very serious. The present study were performed to obtain data on the virgin-uncultivated soils and to clarify the process of their degradation by agricultural practices. Virgin soils were compared with cultivated soils in their neighborhood. Three pairs in Khon Kaen and two pairs in Roi Et were examined for morphological and chemical properties. The virgin soils compared with the cultivated soils had: (1) a much darker surface horizon, (2) a more developed structure of the surface horizon, (3) more and deeper roots, and (4) higher activities of soil organisms in the upper part. The surface horizons of the cultivated soils showed a marked decrease of organic matter, CEC, exchangeable bases and available phosphorus, and an increase of exchangeable acidity as compared with those of the virgin soils. These results suggest that soil fertility in the forests is maintained by internal cycling of mineral nutrients through the soil-plant continuum, and minimum erosion. To restore soil fertility of any cultivated soil to its original level, application of organic matter together with bases and protection the soil against erosion are confidently recommended.
