Comparative Assessment of Three Methods for Soil Organic Matter Determination in Calcareous Soils, Eastern Algeria

Abstract

Soil organic matter (SOM) plays a fundamental role in soil fertility and ecosystem functioning. In calcareous soils, SOM quantification is often challenging due to carbonate interference. This study aimed to compare three common analytical methods for SOM determination: the Anne method, the modified Walkley–Black method, and the Loss on Ignition (LOI) method, with and without decarbonation. Twenty-five soil samples were collected from a calcareous parcel in the Bordj Bou Arreridj region (Algeria), and SOM content was analysed using all methods. The results revealed substantial variability in SOM content across methods, reflecting differences in sensitivity to carbonates and efficiency of organic carbon oxidation. The Anne method, considered the reference technique, yielded the highest mean SOM content (3.61%), followed by LOI without decarbonation (3.41%), the modified Walkley–Black method (2.96%), and LOI with decarbonation (2.55%). Strong correlations were observed between methods, particularly between the Anne method and LOI with decarbonation (R2 = 0.91), confirming the latter as a reliable alternative. Decarbonation significantly reduced SOM overestimation, as demonstrated by paired statistical tests and a large effect size (Cohen’s d = 2.95). Linear regression models were established to estimate SOM from LOI results, providing a cost-effective approach for rapid assessment. These findings highlight the importance of method selection according to soil type, the need for standardised protocols, and the value of LOI with decarbonation as a robust, practical, and economical method for SOM determination in calcareous soils.