Quote:
Originally Posted by Richard
Here in the west, our clay soils often already have a lot of calcium in them so that more calcium is not necessarily a good answer. Our water supply tends to be alkaline as well. A long term plan to keep the soil pH in the 6 to 6.5 range helps a lot. Carbon is sometimes scarce in these soils, so adding more via plant matter, humic acid, etc. can be very beneficial.
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I'm willing to be that there is quite a bit of sodium in the soil as well though and the goal of gypsum is not so much to add calcium for the plants but to add calcium to the soil to change the way the individual soil particles(clay colloids) act. If a clay colloid has a sodium or potassium ion attached to it it tends to stay as a single colloid, however if it has calcium or magnesium attached to it, it can attach to another soil particle and create a larger particle. I think it's pretty hard to overdo calcium especially in the form of gypsum since you aren't altering the pH. From what I recall from my soil classes it is just about impossible to give plants too much calcium. The key is to not add calcium in a form that will raise the pH such as calcium carbonate, but in that case it's not necessarily the calcium but rather the pH change. If you could get your soil to about 6 or 7% organic matter you'd probably have great soil structure for a long time of course that would likely require about 1.5 tons of compost per 1000sqf