embodiment the header wheels 40 are replaced with skid shoe 40 a in some applications it is preferable to place the header ground engaging units below the cross conveyor 20 and or the pick up unit 50 this is so because this location allows the pick up unit 50 to pick up crop material before the ground engaging unit reaches the location of the crop material while the merger 1 is pulled in the direction d in other words placement of the ground engaging units below the pick up unit 50 reduces trampling of the crop material when placed below the cross conveyor 20 and or the pick up unit 50 it is preferable that the ground engaging units are short vertically so as to allow the pick up unit 50 to stay close to the ground and pick up material accordingly in some cases skis or rollers will function better than header wheels 40 as the header ground engaging units as the skid shoe 40 a is typically not used while the merger 1 is in the transport state the skid shoe 40 a will contact the ground only when the merger 1 is in the work state and therefore will usually be used on soil or grass not pavement fig1 depicts the header assembly 60 with another variation of the header ground engaging unit in this embodiment the header wheels 40 are replaced with at least one roller 40 b functioning as the.