INFO WANTED: How to make hard-packed clay soil productive?

[Duncan D. Sterling]

Organization: University of Maryland, College Park

 
TThe soil in the yard around my house consists mostly of clay--so much clay
that the main thing that will grow on it is moss.  I've heard a number of
rumors about lime and mulch, but short of rototilling the yard, and
spending a ton of money on top soil and tiller rentals, what is the best way
to return this soil to the land of the living?

Thanks in advance for any and all replies.

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Duncan Sterling          buffalo at wam.umd.edu   GT750L, KH500A8, CA175K3
University of Maryland    "Yeeehaaa!" - Slim Pickens in "Dr. Strangelove"   
College Park, Md.         "2 strokes are quicker than 4" - anonymous