The main reason for using Horticultural Gypsum is to clean exchange sites in the soil of undedesireable elements namely soduim. However it also cleans away the desireable elements N-P-K etc. We use horticulture gypsum on swim pool water spills or overflows to leach out the salts and acids from the exchange sites. We must come back with a complete fertilizer to refill those elements that are disireable. This is the only way I apply gypsum with out a soil sample test. Then only because swimming pool water is a common problem in my area. OOPs also when we have bad storms and sea water floods.
it is one thing to do a off label applications. It is total stupidity to post it on the world wide web and expect people to approve.
You can lead a Donkey to water but you can't make the Jackass Drink