A multinutrient soil extraction procedure in routine soil testing is attractive. Therefore, it has been suggested to convert conventional soil testing programs into a 0.01 M calcium chloride (CaCl2) multinutrient soil testing program using the relationship between test values of the 0.01 M CaCl2 extractant and those of the various conventional extractants. However, these relationships are often weak and an interpretation of the coefficient(s) is almost impossible. Therefore, a fundamental relationship has been deduced relating magnesium (Mg) extracted by conventional methods, (Mg-ext)a, with Mg extracted by the 0.01 M CaCl2 method (Mg-ext)CaCl2: (Mg-ext)a = [* (Mg-ext)CaCl2,t=t] [*(Mg-ext)CaCl2,t=t * (Q-re)CaCl2]. In this relationship, , , and are related to characteristics of the extraction procedure and Mg-fractions in the soils. The (Q-re)CaCl2 is the actual cation exchange capacity of the soil during the CaCl2 extraction. To test the usefulness of this relationship, 39 agricultural soils with widely differing soil characteristics were extracted with 0.01 M CaCl2 and seven conventional Mg extractants. For six conventional methods, the explained variance of the fundamental relationships was more than 0.92. The explained variance of the relationship among 0.01 M CaCl2 and the 0.1 N ammonium-lactate/0.4 N acetic acid extractant buffered at pH 3.75 was poor when the soils contained carbonates. We conclude that the derived fundamental relationship can be used for the design of a CaCl2 soil testing program for Mg. Preferably, this CaCl2 soil testing program should be validated in pot and field experiments.
van Erp, P. J., Houba, V. J. G., Reijneveld, J. A., & van Beusichem, M. L. (2001). Relationship between magnesium extracted by 0.01 M calcium chloride extraction procedure and conventional procedures. Communications in Soil Science and Plant Analysis, 32, 1-18. https://doi.org/10.1081/CSS-100102989