Lynn,
Timing of the planting can make a big difference also. We do this practice on our properties because it provides great cover within the corn rows and really promotes carryover of the birds. We spray early with round-up to kill the vegetation and then plant when the vegetation starts to die. We prefer to plant and have everything in by the middle of May. We plant and fertilize directly in the row with the planter. We plant on 36" rows and then we do not respray after planting. It is really all about timing and if it is off a little, the competition will typically stunt the corn. It is so much about timing, that we went from renting a planter to owning one. We leave all of our crop stand through the winter and do not harvest any of it. I have attached a few hunting pictures to show what we end up with, but I suspect this is what you are wanting.
The corn is a little stunted in this area mainly due to getting it in around the first of June. The corn is producing some ears, but is not ideal.
This is on an outside row of a field that was planted very late and the outside row is sparce. We sprayed late and the dry summer kept this field from coming great, but the corn did reach maturity and the ground cover is average
This field was planted around the 10th of May. This is what we try to get in each field if possible. You can see from the dogs, the ground cover between rows is extremely thick and the corn is producing and mature. This picture is in the middle of the field and we have left an extra large gap between planter passes.