Formation mechanism of soil aggregates at the foothill of Razor Hill (Che Kwu Shan), Yau Yue Wan, Hong Kong

Abstract

Pedology is the study of the interaction between soil materials and the environment, to understand how the soil materials, including organic matter and minerals under the influence of climate factors, gradually developing into a soil profile. Pedogenesis is the term to describe the development of soil formation, from initially the rock with a thin layer of soil, eventually to a thicker layer and increasing in the number of horizons which can be differentiated by their color, structure, and hence the complex soil profile is established. Soil peds have different characteristic features among the soil profile. For example, granular and/or crumb shape of peds are commonly found in the topsoil. In this study, granular soil aggregates are observed at the soil surface of the foothill of Razor Hill (Che Kwu Shan). In this dissertation project, field sampling was conducted for testing on the soil aggregates. Particle size distribution obtained from Particle Size Analyzer. Mineral identification through the analysis of Scanning Electron Microscopy (EDS) with Energy X-Ray Dispersive Spectrometry (EDS) showed that primary and secondary minerals are present in the soil aggregates, especially clay minerals. These clay minerals provide the binding material in aggregation of peds as it is essential for the constitution in chemical bonding between minerals and organic matter. The soil aggregates observed can be suggested as peds, and the pedogenesis process is an on-going process, it is possible that the soil aggregates are following the soil peds formation mechanism in a particular stage. As the subtropical climate of Hong Kong gives the condition of warm temperature and high humidity which favors the weathering process in physical, chemical, and biological manner. With the four distinct seasons throughout the year, the climate provides the important process of the wetting and drying cycles in the growth of soil aggregates. The properties of soil aggregates were observed, and its physical environmental factors analyzed, were shown to have fulfilled the condition of soil peds formation mechanism.