Mushroom growing medium salt

A friend called this afternoon asking if I had an idea what salt used mushroom growing medium contained that made it too "hot" to be used around plants prior to composting for six months to a year. She had done searches prior to calling and told me she could find nothing specifying the "salt" involved. I speculated that it probably was a nitrate, but....
Any help would be appreciate. BTW, I mentioned this group had a number of knowledgeable people who probably could help. Last week she was particularly impressed with paghat's description about the echinacea problem, including its vectors, that I forwarded to her after she had experienced a similar problem. Personally, I really enjoy paghat's political observations. :)
John
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Actually it's 'salts' in the plural, in particular soluble salts, primarily as a result of too high levels of potassium and ammonia in fresh mushroom compost, much the same as one would encounter with fresh chicken manure (which is often a primary ingredient of the mushroom growing medium). The potassium is very soluble and will leach out rather rapidly and the ammonia will undergo a process of nitrification which will convert it into a usable (and non-burning) form of nitrate but the speed with which this is accomplished is determined by temperature and pH. Best to age it well if the mushroom compost is fresh.
Most bagged mushroom compost has been properly aged, but I would avoid using it on seedlings or with any seed starting medium as young plants and seed germination are particularly sensitive to soluble salts.
pam - gardengal
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information she wanted. :)
John
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