sulfur is used to bring down the PH. There are some clays that are acidic. Pine needles might help as well.
Only thing I can think of is that they have recalled a lot of china drywall. Forget exactly what was wrong with it, but it was corroding the electrical systems in houses and about killing the people too. So, might want to test the board first before you use it, or grow your own materials
Drywall/gypsum will do nothing for correcting alkaline soil. Gyprum is alkaline. You can use it to buffer your soil pH from becoming acidic but it won't help you lower soil pH.
Gypsum immediately decreases the pH of sodic soils or near sodic soils from values often over 9 but usually over 8 to values of from 7.5 to 7.8. These values are in the range of acceptability for growth of most crop plants. Probably more than one mechanism is involved. Ca++ reacts with bicarbonate to precipitate CaCO3 and release protons which decrease the pH. Also, the level of exchangeable sodium is decreased which lessens the hydrolysis of clay to form hydroxides. These reactions can decrease the incidence of lime and bicarbonate induced iron deficiency. (3)
Jonathan Byron wrote:
High quality gypsum is close to neutral when dissolved in water - the acidic sulfur is largely balanced by alkaline calcium. Some gypsum can contain extra sulfur or extra calcium, and might push the pH in either direction. And depending on what else is in the soil, gypsum can react with that and change the pH in either direction.
I cant imagine gypsum or drywall ever lowering the PH. I am no chemistry major though.
This only works in sodic (high salt) soil. We've got a lot of limestone in the ground around here and it will push pH to over 8. Gypsum would do nothing for this.
"Gypsum Helps Reclaim Sodic Soils
Where the exchangeable sodium percentage (ESP) of sodic soils is too high, it must be decreased for soil improvement and better crop growth. The most economical way is to add gypsum which supplies calcium. The calcium replaces the sodium held on the clay-binding sites. The sodium can then be leached from the soil as sodium sulfate to an appropriate sink. Without gypsum, the soil would not be leachable."