Comparative Assessment of Soil Organic Matter Determination Techniques in Semi-Arid Mediterranean Soils: Loss on Ignition Vs Potassium Dichromate Method

IJEP 46(5): 448-458 : Vol. 46 Issue. 5 (May 2026)

Full Text

Maria El-Harram, Mohamed El Baghdadi*, El Hassania El Hamzaoui, Ayoub Outalleb and Atika Mouaddine

Sultan Moulay Slimane University, Geomatics, Georesources and Environment Laboratory, Faculty of Sciences and Techniques, Beni Mellal, Morocco

Abstract

This study compares the Walkley-Black (WB) and loss on ignition (LOI) methods for estimating soil organic matter (SOM) across three landuse types—forests, cropland and bare soil in the Beni-Moussa irrigation perimeter in the Tadla plain, Morocco. Samples of 1 g, 2 g, 5 g, 8 g, 10 g and 20 g were tested using the LOI method to identify the optimal mass for producing results comparable to those of the chemical method. Results showed that both sample mass and landuse significantly affect SOM values. The WB method produced lower SOM values than the LOI method across all soils, with greater variability. However, the LOI method proved highly reproducible, especially with sample masses of 5 g and 10 g. Statistical comparisons using GLM, ANOVA and Mann-Whitney tests confirmed that certain LOI sample masses (specifically 5 g and 20 g) yielded values not statistically different from those of the WB method, particularly in bare and tilled soils. These results support the use of the LOI method as a valid and cost-effective estimator of SOM, provided it is calibrated according to land use and sample mass.

Keywords

Soil organic matter, Walkley–Black method, Loss on ignition, Landuse, Sample mass, Morocco

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