Exploring the link between cation exchange capacity and magnetic susceptibility

Abstract. This study explores the relationship between soil magnetic susceptibility (𝜅) and cation exchange capacity (𝐶𝐸𝐶) across diverse European soils, aiming to enhance pedotransfer functions (PTFs) for soil 𝐶𝐸𝐶 using near-surface electromagnetic geophysics. We hypothesize that soil 𝜅, can improve the prediction of 𝐶𝐸𝐶 by reflecting the soil’s mineralogical composition, particularly in sandy soils. We collected data from 49 soil samples in vertical profiles across Belgium, the Netherlands, and Serbia, including 𝜅 in field conditions (𝜅^∗), low and high frequency 𝜅 in the laboratory, in-site electrical conductivity (𝜎), iron content, soil texture, humus content, bulk density, water content, water pH, and 𝐶𝐸𝐶. We used these properties as features to develop univariable and multivariable (in pairs) polynomial regressions to predict 𝐶𝐸𝐶 for sandy and clayey soils. Results indicate that 𝜅^∗ significantly improves 𝐶𝐸𝐶 predictions in sandy soils, independent of clay content, with a combined 𝜅^∗ - 𝜎 model achieving the highest predictive performance (R² = 0.94). In contrast, laboratory-measured 𝜅 was less effective, likely due to sample disturbance. This study presents a novel 𝐶𝐸𝐶 PTF based on 𝜎 and 𝜅^∗, offering a rapid, cost-effective method for estimating 𝐶𝐸𝐶 in field conditions. While our findings underscore the value of integrating geophysical measurements into soil characterization, further research is needed to refine the 𝜅- 𝐶𝐸𝐶 relationship and develop a more widely applicable model.