The contribution of termites to the microgranular structure of soils on the Uasin Gishu Plateau, Kenya

The structure of many clay soils in tropical Africa is composed of microaggregates that range in size from 0.03 to 1 mm. These structural units are often very stable and known as pseudo-sand or pseudo-silt; their presence is detected from the loamy feel of the soil. This paper tests the hypothesis that termites contribute to a stable microgranular, i.e., finely aggregated, soil structure. A termite mound was selected on pedologically unaffected, clayey weathering material derived from phonolite. The fate of microaggregates produced by termites has been followed through the various stages of mound building. Field evidence was supplemented with microscopic analysis. Development of the mound begins when lumps of soil are detached from the subsoil by termites and carried as microaggregates up to the surface. In the next stage the microaggregates are cemented to form the nest. Breakdown begins when the nest is abandoned and disintegrates by splash and runoff producing colluvium, or is demolished by ants. In the final stage this material is integrated in the soil of the mound. Soil aggregates produced by splash, ants and soil-forming processes have different size characteristics, but the original microaggregates produced by the termites are preserved in the matrix throughout. It is assumed that they owe their stability to impregnation with saliva or other body fluid excreted by the termites. Termites produce also microaggregates in the form of fecal pellets, but these appear to be unstable and are found only in the voids of the soil developed during the last stage.