THE POROSITY OF TROPICAL SOILS AND IMPLICATIONS FOR GEOMORPHOLOGICAL AND PEDOGENETIC PROCESSES AND THE MOVEMENT OF SOLUTIONS WITHIN THE WEATHERING COVER

Abstract

As there is a lack of research carried into the relationship between soil porosity, pedogenesis and geomorphological processes, this study contains an overview of research results on this topic from the 'soil and relief in the tropics' project at the University of Cologne.The macroporosity (volume, poretypes, porefillings, etc.) of 641 tropical soil samples was examined using thin sections. The samples form part of a database project, which allows correlation of field and laboratory parameters. Analyses show a high macropore content even in fine-grained soils and subsoil and saprolite horizons. Pore fillings are mainly found in relic soils on old landscapes, yet the complete filling of pores seems to be the exception. Thus, the passage of solutions and suspensions within a soil cover has, in most cases, only minor restrictions. This suggests that the lateral transport of solutions, which may be crucial for the nutrient supply in areas with depleted soils, may be possible in tropical regions.Pore fillings may also be used to reconstruct polygenetic soil development. They allow a relative dating of soil-forming processes either by establishing a 'pore stratigraphy' or by identifying precipitates that are incompatible with each other in the same horizon.