Must have been a volleyball court. Put an add in Craigslist stating they must load it themselves, if there is access or aerate your lawn in the fall and start top dressing.

Here is a link that might be useful: Propagating Perennials

i'd till it right in to the soil, then till some aged manure in to the bed...but I come from good red clay soil, so there can never be enough stuff to till into the garden for me :)