Fig. 16. (a) Development of the deep-furrow split-packer John Deere HZ drill in the mid-1960s was a major advancement for winter wheat–summer fallow farming because seed could be placed up to 18 cm below the surface into moist soil. This allowed farmers to establish wheat early (late August to early September) for optimum grain yield potential. (b) Deep furrows spaced 41 cm apart help minimize the soil cover over the seed, but winter wheat seedlings still have to elongate through 10 to 15 cm of soil to reach the surface. The drags behind the drill are sometimes used to help stabilize the furrow and reduce the thickness of soil covering the seed. Photos by W.F. Schillinger.