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Purpose <p>Soil cation exchange capacity (CEC), a fundamental indicator of soil fertility, is traditionally determined using either the Kjeldahl distillation method (Kjeldahl-based CEC) or the KCl extraction method (KCl-extracted CEC) following saturation with neutral ammonium acetate (pH = 7.0). Although both methods are widely adopted, they differ in analytical principles, which may result in inconsistencies across datasets.</p> Materials and methods <p>In this study, we developed empirical conversion models linking Kjeldahl-based and KCl-extracted CEC values using 20 soils representative of China’s diverse pedoclimatic conditions.</p> Results and discussion <p>The results showed that Kjeldahl-based CEC values were consistently higher than those obtained by KCl extraction, likely reflecting the inclusion of fixed and organically derived NH₄⁺. Regression analyses between Kjeldahl-based and KCl-extracted CEC values revealed strong linear relationships (<i>R²</i>=0.97–0.98). The robustness of the conversion model was further supported by an independent validation using nine soil samples from Langxi County, which demonstrated an excellent agreement between measured and predicted values (<i>R</i><sup><i>2</i></sup> = 0.997, <i>P</i> = 1.56 × 10<sup>− 11</sup>). The validated model was subsequently applied to historical Kjeldahl-based CEC data from the 1980s Second National Soil Survey of China in Langxi County, Anhui Province, and compared with newly collected data from 2024 obtained using the KCl extraction method. After conversion, the results indicated a 15.3% increase in soil KCl-extracted CEC over the past four decades, which was closely associated with increasing soil organic matter content.</p> Conclusions <p>These findings offer critical insights into long-term soil fertility dynamics and provide a standardized framework for reconciling CEC datasets across analytical methods and temporal scales.</p> Graphical Abstract <p></p>

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Comparison of soil cation exchange capacity determined by ammonium acetate saturation followed by KCl extraction or Kjeldahl distillation

  • 期刊论文

  • 发表日期：

    2026年3月28日

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  • Jun Jiang,
  • Feng Zhang,
  • Guoxing Lu,
  • Ruhai Wang,
  • Enzhe Xie,
  • Tianhua Feng,
  • Xianli Xie,
  • Zhineng Hong,
  • Renkou Xu

摘要

Purpose

Soil cation exchange capacity (CEC), a fundamental indicator of soil fertility, is traditionally determined using either the Kjeldahl distillation method (Kjeldahl-based CEC) or the KCl extraction method (KCl-extracted CEC) following saturation with neutral ammonium acetate (pH = 7.0). Although both methods are widely adopted, they differ in analytical principles, which may result in inconsistencies across datasets.

Materials and methods

In this study, we developed empirical conversion models linking Kjeldahl-based and KCl-extracted CEC values using 20 soils representative of China’s diverse pedoclimatic conditions.

Results and discussion

The results showed that Kjeldahl-based CEC values were consistently higher than those obtained by KCl extraction, likely reflecting the inclusion of fixed and organically derived NH₄⁺. Regression analyses between Kjeldahl-based and KCl-extracted CEC values revealed strong linear relationships (R²=0.97–0.98). The robustness of the conversion model was further supported by an independent validation using nine soil samples from Langxi County, which demonstrated an excellent agreement between measured and predicted values (R2 = 0.997, P = 1.56 × 10− 11). The validated model was subsequently applied to historical Kjeldahl-based CEC data from the 1980s Second National Soil Survey of China in Langxi County, Anhui Province, and compared with newly collected data from 2024 obtained using the KCl extraction method. After conversion, the results indicated a 15.3% increase in soil KCl-extracted CEC over the past four decades, which was closely associated with increasing soil organic matter content.

Conclusions

These findings offer critical insights into long-term soil fertility dynamics and provide a standardized framework for reconciling CEC datasets across analytical methods and temporal scales.

Graphical Abstract