Soil structure controls many soil functions including water and air (gas) flow in soil. Although soil structure has received considerable attention by soil scientists, structure is one of a limited number of soil properties that have not been sufficiently quantified, and to date there are no good methods or techniques for doing so. Soil structure is generally unstable in time and it is nonuniform in space, and it is affected by changes in climate, biological activity, and soil management practices (Hillel, 2004).