16 巻 (2007) 3 号 p. 215-231
In a region of Lower Northern Thailand, the traditional agricultural system has recently been changing toward a more intensive farming system by shortening the fallow cycle and several years of continuous cropping with significant fertilizer application. This study characterized soil fertility levels under the current intensified shifting cultivation systems, by comparison with the fruit tree plantations in the same area and the traditional shifting cultivation systems reported in the previous studies. Soil samples at surface and subsurface layers were collected from thirty study sites. Those study sites were grouped into 4 locations based on topography and parent material. Based on the PCA analysis of soil properties, soil fertility levels were mainly dependent on locations rather than the differences in land use types. However, some of the soils under maize field and fruit tree plantation showed a very low content of organic matter, suggesting occurrence of soil degradation in terms of organic matter. Burning of biomass still played an important role under the current intensified shifting cultivation systems, which brought positive effects to the soil fertility to alleviate soil acidity and supply exchangeable basis and available phosphorus. In contrast, because appreciable amounts of nitrogen seemed to be lost from soil ecosystems during cropping period, appropriate fertilizing methods should be developed to maintain the level of available nitrogen and to prevent environmental pollution.