Abstract: Disclosed herein is a device adapted to be pulled by a tractor, which device comprises an elongated frame having forward and rearward ends, wheels supporting the rearward end of the frame for travel along the ground, a mass movable on the frame between the forward and rearward ends, a sled having a relatively large ground engaging surface, a guideway on the sled and a slide located on the forward end of the frame and movable in the guideway in the fore and aft direction and adjustably connected to the guideway, and a connector on the sled adapted for attachment to the tractor for pulling of the device by the tractor along the ground.