Referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, FIG. 1 illustrates a side elevation view of a single row unit (10) of a conventional row crop planter such as the type disclosed in U.S. Pat. No. 7,438,006, the disclosure of which is hereby incorporated herein in its entirety by reference. As is well known in the art, the row units (10) are mounted in spaced relation along the length of a transverse toolbar (12) by a parallel linkage (14), comprised of upper and lower parallel arms (16, 18) pivotally mounted at their forward ends to the transverse toolbar (12) and at their rearward end to the row unit frame (20).