If your trying to spray corn post emergence I would probably stick to a boom sprayer. Although if the corn is short enough to use an ATV to spray maybe not. If you are spraying under 9-10" corn I would consider a boomless. How many acres are you spraying that it's taking 5 hours? Might just make some adjustments to what you are using now. With 25 gallons I would be spraying at least 2 acres per tank. You might already be doing that. Just want to make sure. If it was taking me that long I would get a bigger tank for the tractor and go with a boom sprayer that fits in with your row planting pattern. Meaning if your using a 4 row planter on 30 inch center you would want 20' boom to cover 8 rows at a time.