1. Haas, A. R. C., pH for healthy growth of citrus. Calif. Citrogr.23, 158?181 (1938).
2. McGeorge, W. T., Acidulated fertilizers for Arizona soils. Arizona Agr. Exp. Sta. Tech. Bull.101 (1943).
3. McGeorge, W. T., Relation of potential alkalinity to the availability of phosphate in calcareous soils. Soil Sci.39, 443?452 (1953).
4. Aldrich, D. G., Effect of soil acidification on some physical and chemical properties of three irrigated soils. Soil Sci. Soc. Am. Proc.13, 191?196 (1949).
5. Roy, P. K., Effects of sulphur and organic matter on phosphate availability in calcareous soils. D.I.C. Thesis, Imperial College, London (1953).