Describe the Mapes plow. Why is the motion in the soil of one and a half inches sufficient? How does the oxidation of the particles of the soil resemble the rusting of cannon balls in a pile? The sub-soil plow is an implement differing in figure from the surface plow. It does not turn a furrow, but merely runs through the subsoil like a mole—loosening and making it finer by lifting, but allowing it to fall back and occupy its former place. It usually follows the surface plow, entering the soil to the depth of from twelve to eighteen.
