Results show that by-product gypsum is effective in increasing yields of several field crops grown on acid soils by ameliorating aluminum toxicity and supplying needed calcium. In addition, gypsum application resulted in a decrease in penetration resistance of subsoil hardpan layers. This, coupled with the reduced toxicity of the subsoil, promoted deeper root penetration and greater access to soil moisture, thus reducing drought stress. Phosphogypsum and mined gypsum were equally effective for this purpose. Deep tillage of lime is a practice that has been used to reduce subsoil acidity, but gypsum, because of its greater solubility, can be used effectively through the less-costly method of surface application.