Posted: Yesterday at 23:51
That looks more like dumped subsoil with builders waste mixed in. That will be job and a half to rectify.
I'd incorporate not just garden compost, but horse manure and if I'm right it won't matter if its fresh or aged and leave it for a year to recover and let the worms and micro organisms get to work. It will take that long to get anywhere. Let the light and air get to it, nature will do the rest.