Strength of soil is the resistance to breaking or deformation. Strength is determined
by the force just sufficient to break or deform a 20 mm diameter piece of soil when
a compressive shearing force is applied between thumb and forefinger. The 20 mm piece
of soil may be a ped, part of a ped, a compound ped or a fragment.
Forces 0 to 5 are equivalent to the following dry consistence classes in the ‘USDA
Soil Survey Manual’ (Soil Survey Staff 1951): 0 Loose 1 Soft 2 Slightly hard 3 Hard 4 Very hard 5 Extremely hard