I've read that before also. With an over 7 ph there is no free hydrogen for the potassium to knock off and attach to the soil.

No disrespect to all the posters but the yield goal is 140 for corn. There is no way you could get a decent ROI on applying 400-500 lbs of potash. 

IMO fertilize for crop removal with a little extra for P & K. Maybe a couple gallons of K-thio with your sidedress if you are a sidedresser.