Question
I live in south central PA and have a blue grass rye lawn started 5 years ago. The top soil is poor.  Will applying 1/2 inch of compost present problems?  I plan to plug aerate prior to application of the compost.

Thanks  

Answer
If you are not putting anything under that grass, Frank, like Weed B Gone or Roundup, that would hurt earthworms, you risk disturbing your soil structure by aerating.

Yes, Compost is great to add.  Humus, ditto.  Aged manure, ditto.

Even better: humic acid ("humic substances" are the dark matter you see in humus) and compost tea.  A half inch is a LOT of compost, but not if you have earthworms to mix things up a little.

Now, although I understand your intention is to break up the compacted soil, you risk killing Earthworms under that soil, and you are not really solving the compaction problem because you are disturbing the soil structure even with a little aeration - sort of like a mini-tilling.  A little patience is needed for this project.  I hate to sound religious about it, but it's one of those things that's going to be done in God's time.

The missing ingredient in your topsoil is organic matter.  Not air.  Earthworms are Nature's underground soil builders.  If you soil is compacted, earthworms can till it - gently - and build rich, thoroughly wonderful dirt for your grass.  I vote against aeration and in favor of compost tea and humic acid.

Earthworms feast on microbes in healthy soil.  Earthworms are generally considered by scientists to be "the largest contributors to soil fauna biomass and key players in organic matter decomposition and soil macropore development."

Compost tea is a concentrate of microbes that Earthworms adore; dosing your turf with compost tea will speed up any decomposition of microbe-friendly things like dead leaves, grass clippings (organic only), coffee grounds, manure and humus.  The more microbes, the happier the Earthworms.

One thing you can count on Earthworms for is gentle, thorough, deep soil aeration.  But they can't do anything in a hostile environment.  If you use chemicals, you have a hostile, unfriendly-to-Earthworms situation.

Now, if you're assuming that fungicides are only bad for fungus in the grass, I have to point out a recent study at Ohio State's Soil Ecology Program (www.ksu.edu/biology/bio/meetings/abstracts.html) that proves you wrong.  Researchers studied the effect of three popular Fungicides.  They noted that Fungicides lowered soil microbial activity, altered Nitrogen and increased leaching of nutrients; the fungicide Captan did the most damage.

Just do everything you can to keep the Earthworms happy, and lay on the Compost.  Take your mulching seriously (and it sounds like you are quite serious about that, as you have given all this a great deal of thought).  Watch the pH (you don't want your soil pH lower than 6.5, which is the perfect pH for grass).  And see what happens.

Please keep in touch and let me know if you have any questions.  Thanks for writing!