I live in the middle of corn country and I can tell you for certain around me that birds do feed in tilled fields.
that said,they generally visit those fields later in the day towards dark as there isnt much cover for them to hide in like fields that havent been turned under.
when I hunt tilled fields I walk the fence lines if there are any as the birds will be sitting in the grass/brush waiting to feed.
I will also hunt any terraces in those fields,it is amazing how many birds will hold up in even the least amount of cover on a terrace.