G'DAy Crebourret,
If the manure was your usual herbivore (horse, cow etc) the seeds and seedlings should be OK. The real problem is fresh chook (or other bird) poo because of the high nitrogen content which will "burn" the young plants. After aging for a couple of years though, even the chook poo should be OK.
To reduce the tilth for seeding etc. have you tried breaking things up with a hoe, or maybe a 3 - tine cultivator? Chop up the surface with the hoe (oh my aching back!)

or drag the cultivator across the top, which will break some bits up or at least drag the big ones out of the way.
Hope this helps and lots of luck!
Nev