Effect of fallow length on soil structure, hydraulic properties, and soil organic C in a swidden cultivation system of western Thailand

Abstract

Changes in soil structure, hydraulic properties, and organic C content were investigated in a swidden cultivation system, and an adjacent natural forest, in western Thailand. Using the chronosequence approach of sampling closely-spaced sites, differences in soil properties were assessed and an evaluation made of changes to such properties over a typical fallow period of 10 years. Such aspects have important repercussions not only for the successful reestablishment of vegetation after cultivation and the sustainability of that swidden system, but also for the influence they have on plant growth rates, soil erosion, and local hydrology. The soil structure remained in good condition for all fallow years tested, compared with undisturbed forest, as shown by the maintenance of low bulk density values and high porosities. The already low plant available soil water did not change and organic C contents were maintained at reasonably high levels for all treatments, although assumptions were made about the changes in quality. The lack of changes are assumed to be due to the low intensity of the farming method and the inherent soil properties giving it resilience to change. ©2003 Trop. Agric. (Trinidad).