a tandem comprising the combination of leveller and covering wheels for use in no - till or direct - till sowing machines . the leveller wheel has a semipneumatic tread including a cavity next to the furrow opener disk to make room for the soil removed from the ground by the latter without compacting it . the cavity spans between one - and two - thirds the breadth of the tread . the shape of the cavity follows the profile naturally formed by the elevated rib of soil formed on the ground on which the covering wheel operates . the cross - section area of the cavity is 30 % greater than that of the deepest expected furrow . the covering wheel is provided with conical studs which radially project outwards from the tread , at a 5 ° angle to the wheel plane , the flat rolling band being slanted at 30 ° to the horizontal .