David E. Ross wrote:
Today, I went to buy gypsum to apply to my clay soil before the winter
rains begin. While I never buy plants at a hardware store or lumber
yard, I do buy tools and supplies at such stores.

I went to a nearby hardware store (about 3 miles from my house) and
took a 40-pound sack of gypsum to the register. With a senior-citizen
discount of 5%, the clerk said that it would be $12+change. I left
the sack at the register and drove to a favorite nursery about 12
miles away. There, I bought a 50-pound sack of gypsum for under $9.

That is correct: 25% more gypsum for 25% less money. Both were 92%
CaSO4 (calcium sulfate).

What effects do you see from applying gypsum? Is it anything obvious? Are repeat
application useful?