It wouldn't surprise me. Cornmeal keeps seeds from germinating. If you sprinkle corn meal in a garden bed with mature plants, it will keep new weeds from growing. Maybe that has something to do with it.
I would be surprised if the Scratch and Peck was killing the ground though since thats only...
Scratch and Peck sprouts. I sprout grains for my birds and use Scratch and Peck as my sprouting grains. I might understand if pellets were killing things, but Scratch and Peck shouldn't.
At this point I'm assuming that the wild birds are finding the feed your throwing out, and scratching up...