Noydb said:

Pat Kiewicz wrote:


But the volume of compost has shrunk to 1/8 of the original
volume. The compost now has twice as much weed killer (per volume) as the
starting material. (The shrinkage is not exaggerated, either, based on my
experience.)

I don't want to start a flamefest, but I don't think I have ever lost
anywhere near that much volume. Probably no more than 1/3 lost, 2/3 kept. I
use, almost exclusively, grass clippings and tree leaves with some kitchen
scraps for good measure. I turn perhaps twice a week (depending on what the
internal temps are), watering each time.

Does anyone have a link to a study on such shrinkage?

Perhaps 1/8 is a bit low. However, my compost regularly shrinks in volume to
less than 1/4 of the original amount. I think that is probably because of the large
amount of shredded leaves that goes into each batch and the fact that the curing
pile is regularly worked by redworms. Many of my batches also contain a large
amount of chopped cornstalks. (Both of these materials really compost down
in volume a LOT.)

Here's a study using various material combinations that shows reductions in
volumes varying by mix, with yeilds as low as 17% (reduction in volume as
much as 83%):

http://www.cast.ilstu.edu/ksmick/Com...mpostbuild.htm

The basic problem with highly persistant herbicides in the composting process
is that the volume reduction of the composting process equals or exceeds the
breakdown percentage of the herbicide. Thus the resulting compost is still
toxic to some plants. Clopyralid is the most problematic herbicide and is
widely used on lawns and hayfields. Picloram and triclopyr can also persist
through the composting process. Clopyralid can persist even in composted
manure.

Potatoes, tomatoes, peas and beans are the veggie garden plants most likely to
show signs of herbicide toxicity at low doses. (Which is why I brought up the
issue in this thread.)

I do not bring in any grass clippings from outside my property and avoid
using commercially made compost in my veggie garden (though I sometimes
run out of homemade compost and use bought compost on my squash beds only).
--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)