Seed corn nurseries are still planted with a check system.  The plots are short runs with a gap between plots.  The check cable trips a cone seeder, and a crew rides the planter dumping little envelopes of seed into the cone while the planter is in the alleyway between plots.  Some of them are controlled with GPS now.  Considering the typical plot planting crew consists of a driver, six riders, two tray carriers, two irrigation technicians, and the guy with the clipboard making sure everything is where it is supposed to be, eliminating the check cable  is one less hassle to bother with.