RELATIONSHIP BETWEEN MAGNESIUM EXTRACTED BY 0.01 M CALCIUM CHLORIDE EXTRACTION PROCEDURE AND CONVENTIONAL PROCEDURES

Abstract

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 = α + [β* (Mg-ext)_CaCl2,t=t]+[λ*(Mg-ext)_CaCl2,t=t * (Q-re)_CaCl2 ]. In this relationship, α, β, and λ 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.

ACKNOWLEDGMENTS

Acknowledgments are expressed to Professor J. Loch and to Dr. I. Jaszberenyi of the Agricultural University of Debrecen in Debrecen, Hungary, to Professor M. Fotyma of the Institute of Soil Science and Plant Cultivation in Pulawy, Poland, and to Dr. J. Baier and V. Baierova of the Research Institute of Crop Production in Praque, Czech Republic, for the soil chemical analyses at their Institute and their critical comments on earlier versions of the manuscript.