Field clay loam and sandy loam were tilled with tillage blades at different rate angles and depths. The loosened soil porosities at different depths were determined in situ in the soil furrow. In the clay loam, the effects of depth of tillage and their interactions on soil porosity were highly significant at the 1% level. In the sandy loam, the effects of the interactions of the tool rake angle with the blade width, the depth of tillage and their interactions on soil porosity were highly significant at the 1% level. In both soils, there were great significant differences between the porosities of the untilled soils and those of the tilled soils. It was therefore possible from these results to design and operate tillage implements to achieve the required tilled soil porosity and subsequent conditions. The importance of this is that tilled agricultural soil susceptibility to erosion by wind and water can effectively be minimized.