I've thrown bio-degradable targets for near 14 years, majority white flyers, some Caldwell, and some Lawry.
all have been shot out of the same machine over a small cliff onto a hay field, I continue to harvest hay every year, the one exception was last year when there was no rain. I don't notice the breakdown, but there are obvious less broken targets on the ground every year. The breakdown will happen a lot quicker
if the broken pieces are broken down even further. We still find the odd complete target, which has been sun bleached and extremely faded, but is not broken down. With out help, don't expect to see the those clays disappear any time soon.