1. Amer, F., Bouldin, D. R., Black, C. A., and Duke, F. R., Characterization of soil phosphorus by anion exchange resin adsorption and P32-equilibration. Plant and Soil 6, 391?408 (1955).
2. Birch, H. F., Relationship between base saturation and crop response to phosphate in acid soils. Nature 168, 388?389 (1951).
3. Bondorff, K. A., Studies on the phosphoric acid content of soil. VI Solubility of soil phosphoric acid in dilute sulphuric acid. Tidsskr. Planteavl 55, 185?210 (1952).
4. Boyd, D. A., The relationship between crop response and the determination of soil phosphorus by chemical methods. II. Tech. Bull. Minst. Agr., Fish and Food, H.M.S.O. London. 13, 94?102 (1965).
5. Bray, R. H. and Kurtz, L. T., Determination of total, organic and available forms of phosphorus in soils. Soil Sci 59, 39?45 (1945).