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That too. It isn't used in casing mixes simply to avoid clumping, although it does improve texture. For use in casing mix and manure/compost, it adds calcium and sulphur, which are both necessary for proper fruitbody development. As a result of the calcium and sulphur, gypsum is also a buffer that prevents wild swings in ph, always attempting to return the mix to neutral.
Blue, I'm curious what kind of ph probe you use that can be calibrated to .1 ph? The only ones I know that are that accurate are the bulb type commonly used for hydroponics. Those are intended to be used in clean, clear liquids in my experience, and are not accurate in soil. The probe type ph testers that use two dissimilar metals are so inacurate as to be unusable. I've found as much as a difference of +/- ph3 just due to how much moisture is in the sample. I'm just curious what type of tester you're using. I use the paper strips that change color, and use them by squeezing out some of the water into a clean dish and testing that. Be sure to wear gloves so the sweat on your hand doesn't contaminate the reading. I've used up to a tablespoon of horticultural hydrated lime per cup of peat, and still had the ph settle out in the mid 8 range within 24 hours.
RR
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