One of the reasons for the irrigation is the crop. It's not just corn, but seed corn. There is a lot of it grown in our area (Northern Indiana/SW Michigan). From what I've heard, the seed corn companies are very specific about everything to do with the crop. Prep, planting, fertilizer, weeds, bugs and water. Had a crop duster working the fields around us just last week.
This time of year it's easy to tell the seed corn fields as every sixth row has been knocked down. Those were the polinator rows but won't be harvested. The tassles were taken off the other rows a while back by the famous detassling crews.
I've heard it's very expensive to grow seed corn but the payback is of course, much higher. If anyone knows more about it, please jump in. I'd like to know more myself.