Depending on where you are, soil amendments will break down at different
rates. If you are in the south or deep south, the heat, humidity, and rain
create ideal conditions for the breakdown of organic materials. So just
piling this kind of stuff on top of your beds is fine - it will break down
quickly, the worms will pull some of it down into the clay, and plant roots
will follow those worm holes into the clay right along with it. Of course,
this also means that you have to replenish that kind of mulch frequently. On
the other hand, organic materials in cool/cold climates, especially ones
that are dry in summer break down much more slowly. When I lived in north
Florida, I had a gardener friend come to visit me in February. I had raked
all the deciduous tree leaves into large piles around the bases of all my
trees. (I had a grove of wild black cherry trees and native persimmons). He
was all set to put all the leaves into bags and haul them away. I said, "no,
the leaves will all be gone by the end of April". He didn't believe me,
until I took pictures that April to to prove it to him. Where he lives (the
inland Northwest) a pile of maple leaves piled around the base of a tree
would still be there, just shrunk a little bit and a touch darker, one year
later.....lol