you are in luck. I have been converting cutover woods, with stumps, roots, rocks, etc. You are already starting with fertile rock free, flat ground! harrow it when the ground is dry enough to "shatter." earlier when it is moist, and you have made a huge mistake. after silage is mostly harrowed in, add nitrogen. corn is a heavy feeder and the ground likely needs it. chicken litter will do just fine. you should be able to broadcast fescue and have it grow, better to drill it in with grain drill. you will be just fine.