[USCC] Sulfur

[Chaney, Rufus]

Dear Ron et al:

You may recall Frank Gouin's use of flowers of sulfur to reduce the pH
of the old calcareous biosolids compost from DC/MD so he could grow
Azalea. He didn't have to go to extremely low pH because the compost was
high in Fe, and the main problem with high pH media for Azalea is Fe
deficiency. The Baltimore compost (Orgro) is about pH 6.5-7, high in Fe,
and is a good substrate for Azalea as sold.

He mixed commercial flowers or granulated sulfur with the compost and
waited until the reaction was completed. That can take many months. The
oxidation of sulfur is a biological activity, and depends on particle
size of the sulfur. Mixing during the process can speed it up if only
because mixing distributes the acidity and remaining limestone particles
in the compost.

As a rule, one would avoid trying to acidify such a compost. Only a few
plant species have trouble with neutral pH organic media, including
especially azalea and rhododendron and blueberry. Most other acid
requiring plant species don't have as much trouble as these because of
the other qualities of compost. So your customer could label the product
as not for use with acid requiring plant species and give a list, or
they could go about the acidification using sulfur.

Because the amount of sulfur needed to acidify is complex, I can't give
you a simple formula. I have used 1 mole S for one mole CaCO3 equivalent
to estimate needed sulfur, but the degree of mixing is very important.
And giving the mixture time to complete the oxidation of the sulfur. And
then when you have gotten a batch acidified to equilibrium, if the pH is
too low, adding a little of the normal alkaline compost back to the
mixture to get the final needed pH. The reaction of lime in compost is
pretty rapid, so you can make experimental mixtures, let them sit moist
for several weeks and then measure final pH to work out how much
alkaline compost to add back to get say pH 6.5 or so. But the
oxidation/acidification is so slow that you can't really do a test
incubation unless you are willing to wait for 6 months to be sure the
reaction is complete. A couple of months will not assure that all the
sulfur was oxidized. And you don't want to sell a product with sulfur
remaining which can oxidize after sale and produce an aluminum toxic
compost when applied to soil. 

Frank reported on what he did in some of his papers, maybe in Compost
Science/BioCycle in the 1980s.

Regards,

Rufus Chaney
Beltsville, MD
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Sent:	Thursday, June 12, 2008 8:28 AM

To:	compost

Subject: [USCC] Sulfur

Hello Compost World,


Has anybody out there had any 'real' success adding sulfur to compost to
reduce its pH?



Thanks,
Ron
Ron Alexander