Estimating cation exchange capacity from agronomic soil tests: Comparing Mehlich-3 and ammonium acetate sum of cations

Soil cation exchange capacity (CEC) measures the capability of soils to hold and release nutrients. It is an important measure for classifying soils and planning nutrient additions, but it is not included in routine soil tests offered to farmers. In this study, we compared CEC measured with standard laboratory practices (neutral ammonium acetate [AAc]) with CEC estimated from agronomic soil test data (Mehlich-3 and AAc). We applied previously published estimation methods to a dataset of 48 soil samples. Based on the results, traditional methods underestimate measured cation exchange capacity by 36% for Mehlich-3 and 24% for AAc. The estimation can be improved by including aluminium (12% overestimate) or by fitting a localized pedotransfer function (3% underestimate), which offers a possibility for informing land managers about their soil nutrient holding capacity without adding costs to the analysis.

Automated summary

This study found that traditional methods underestimate soil cation exchange capacity, which can be improved by including aluminum or fitting a localized pedotransfer function.