Applying a Geopedologic Approach for Mapping Tropical Forest Soils and Related Soil Fertility in Northern Thailand

Abstract

This chapter describes the application of a geopedologic approach for delineating and characterizing soil units and related soil fertility in tropical forest highlands of northern Thailand. The study area contains four types of landscape including mountain, hilland, piedmont, and valley, and five types of parent material including igneous, metamorphic and sedimentary rocks. Soils are distributed over three slope positions, i.e. summit, backslope, and footslope. Soil variability is high, including Oxisols, Ultisols, Alfisols, Inceptisols, Mollisols, and Entisols, found either in consociation or association. A mathematical approach for analysing relations between individual soil bodies was applied to study the soil fertility variation as related to the categorial levels of a hierarchic geoform classification system. This relationship was displayed by means of numerical values of the Similarity Index (SI) and the Fertility Distance (FD), computed by integrating eight soil properties (pH, C, N, K, CEC-soil, CEC-clay, clay, and base saturation) assumed to influence soil fertility. The study showed that the geopedologic approach for characterizing soils of this complex area was suitable and allowed the results obtained in sample areas to be extrapolated to similar areas. It has the advantage not only to be based on strong integration of geomorphology and pedology, but also to take into account the parent material at lower categorial levels of the system.