How much limestone with a CaCO3 equivalent of 90% would you need to apply to eliminate exchangeable aluminum in an Ultisol with CEC = 8 cmolc/kg and an aluminum saturation of 60%? The ill effects of...

How much limestone with a CaCO3 equivalent of 90% would you need to apply to eliminate exchangeable aluminum in an Ultisol with CEC = 8 cmolc/kg and an aluminum saturation of 60%?

The ill effects of acidity in subsoils can be ameliorated by adding gypsum (CaSO4 · 2H2O) to the soil surface. What are the mechanisms responsible for this effect of the gypsum?