Abstract

(Introduction):  The most common method to determine the organic matter content of soil is the “Walkley-Black” method, but this method has environmental disadvantages due to the use of the toxic potassium dichromate. As an alternative, the loss on ignition method arises. Both present significantly different results because the ignition method can report higher data due to the presence of clays and because it considers all the organic content of the sample, unlike Walkley-Black method, which considers only the compounds with longer chains.

(Objective):  The relationship between the organic matter content determined by Walkley-Black and loss on ignition was determined considering the clay content.

(Methodology):  60 soil samples from northeastern and central Honduras were studied. The clay content was determined through the Bouyoucos method. The organic matter content was determined by the Walkley-Black method and by the ignition method following the guidelines by the international standards AASHTO T 194-97 (2018) and AASHTO T 267-86 (2013), respectively.

(Results):  A valid linear relationship was found between the organic matter content determined by Walkley-Black and the loss on ignition regardless of the clay content. It was possible to establish an interpretation range for organic matter content for the loss on ignition method from the typical interpretation ranges reported for Walkley-Black organic matter content.

(Conclusions):  The results of this study showed that it is possible to use the ignition method as an alternative to Walkley-Black.

Keywords: Dichromate; loss on ignition; organic matter; Walkley-Black