Originally Posted by Cadzilla
My simple explanation and understanding is that topsoil is aged compost and the dirt you speak of is subsoil.
The random nature of composted materials is no different than the random makeup and nature of any particular topsoil one would spread so I'm not sure what you mean when you talk about different soils building up over time.
Now I do deal with soil interfacing when sod is used but thats generally because there was no topsoil and it was planted over subsoil causing issues.
The microbial activity is different in composted materials well before they turn into a topsoil type material so in that sense youd probably see benefit from that.
Topsoil is not aged compost... topsoil has mineral components that are permanent parts of the soil,,, such as sand and clay... they do not reduce in size until they are virtually nonexistant as compost does...
That is why, when you add topsoil year after year the elevation will rise... when you add compost year after year the ground level stays the same... the soil is enriched with OM and dirt is just mineral particles w/out OM...
I hope my comments make more sense this time...