Study of soil porosity with mercury porosimetry and image analysis on backscattered electron scanning images (BESI). Application to tilled "crusting soils" in Zimbabwe

Samples were collected from wheel-traffic and seed-line areas of a crusting soil in Zimbabwe. The pore-size distributions obtained by mercury porosimetry and image analysis of backscattered electron scanning images were compared. The two methods show; (i) a decrease m porosity under the wheel lines associated with hardening; (ii) two classes of pore, the first created by aggregate packing and biological activity, and the second by packing of skeleton panicles with the porous clay phase; and (iii) no difference in volume of each pore class. However, the two pore-size distributions show a difference in the modal pore size of each class, which is higher in image analysis than in mercury porosimetry. This difference arises because mercury porosimetry shows the size of necks in the pore network whereas image analysis measures the size of randomly intersected pores.