Cover the area with black plastic sheeting. We did this awhile back to an area with very poor hard clay soil. We then covered the plastic with mulch. The next time we planted in that area, the worms had turned the soil into very nice dark garden soil! I'd chop up everything first with the lawnmower if possible, as another answerer suggested.

Run a lawn mower over it and then till it into the soil.
That's what farmers do to the corn stalks after harvest.