A Single Field Measurement for Estimating Saturation Percentage, Cation Exchange Capacity, and Organic Matter Content of Soils

Abstract

The need often arises to appraise soils for agricultural or environmental uses. Field evaluation of parameters can give timely information about soil quality, often at a fraction of the cost of laboratory analysis. The specific gravity (SG) of a saturated paste (sat. paste) made on-site can be measured using a portable mud balance. For 71 soils from western Canada, the sat. paste SG was correlated with the saturation percentage (% sat.), cation exchange capacity (CEC), and organic matter content (% OM). Empirical power functions of the SG matched data for each of these parameters. The empirical SG function for % sat. corresponded with published data for soils from the western United States as well. Values of SG in the range 1.0 to 2.1 thus indicated % sat. values ranging from 20 to 400 (with r²=0.97), CEC from 4 to 100 cmolc kg⁻¹(r²=0.72), and OM from <1 to 50% (r²=0.80). On appropriate soils, estimates of these parameters calculated from the SG of a sat. paste could therefore be used, together with a hand-texture assessment, for field appraisal of items such as site remediability, sensitivity to contamination and crop production potential.

Acknowledgments

The author was employed at Norwest Soil Research Ltd., Edmonton when this work was done. I thank Doug Keyes and Keith Lepla for valuable discussion, and Nancy Willms for collecting and shipping the soils from Manitoba. Cathy Ngo prepared and did the measurements on saturated pastes. I thank the other technical staff at Norwest for determinations of % OM and CEC.