As the acres on a John Deere single disc drill or air-seeder accumulate over 200-300 acres per row, the holes which mount the seed boots to the arm become worn and/or egg shaped as illustrated left.
This wear (together with wear in the seed boot holes, plus the bolt which mounts the boot to the arm) can all add up to cause significant forward/backward seed boot movement which translates into upward/downward movement. This excessive vertical movement has been found to significantly compromise seed placement, especially when seeding shallow and/or when working at higher speeds in no-till conditions.
