Abstract: An elongated downwardly opening housing is provided for lengthwise advancement over the ground and includes mounting structure for dependingly supporting the housing from a farm implement tool bar. The housing includes front and rear transverse journaled horizontal shafts each having a pair of axially spaced circumferentially spiked wheels mounted thereon for rotation therewith. Corresponding ends of the shafts project outwardly through opposite sides of the housing and have aligned sprocket wheels mounted thereon. The sprocket wheel carried by the forward shaft is at least slightly greater in diameter than the sprocket wheel carried by the rear shaft and an endless chain is trained over the sprocket wheels drivingly connecting the forward shaft or front shaft to the rear shaft.