I'm have 1/2 acre lot which has mostly clay spread over it that was dug out
from the basement when the house was built. In some areas the construction
machinery packed the clay very hard for about 1-2 inches on the top. This
weekend I had 2-3inches of aged cow manure spread over the top and tilled in
as much as possible. The hard areas would not till as it was too hard.

I want to seed grass but I was told that the manure is too rich (I don't
know how to tell) and that it will burn the grass. What can I do to loosen
up that top clay? Will manure do that? What do I need to do before I seed
grass? How old does the manure have to be so it's not too rich?

Thanks,
Peter