Analysis of Porosity in a Tilled Crusting Soil in Zimbabwe

Samples were collected in a tilled ''crusting soil'' from zones with different structures and their porosity was analysed with mercury porosimetry. The results showed three types of elementary pore volumes that differ in both the size and origin of the pores. The first type of elementary pore volume results from the packing of clay particles, and the second one mainly arises from the packing of silt and sand particles with the porous clay fraction. Their variations are mainly related to the clay content. The third elementary pore volume is related to tillage and biological activity, but there is no close relationship between its variation and the type of structure. These results obtained with mercury porosimetry are consistent with observations on thin-section images, using scanning-electron microscopy with backscattered electrons.