1. Adams S N, Honeysett J L, Tiller K G and Norrish K 1969 Aust.J. Soil Res. 7, 29–42
2. Egner, H., Riehm, H., and Domingo, W.R. 1960. Investigations of the chemical soil analysis as a basis for the evaluation of nutrient status in soil.II. Chemical extraction methods for phosphorus and potassium determination (In German). K.Lantbruks Hogsk. Ann. 26:199–215.
3. Jiang, Q. and Singh, B.R. 1993. Water, Air, Soil Pollut.(in press)
4. Kabata-Pendias A and Pendias H 1984 Trace Elements in Soils and Plants. CRC Press Inc. Florida. 315 p.
5. McLaren R G, Lawson D M and Swift R S 1987 J. Sci. Food Agric. 39, 101–112.