Determination of organic matter in soils of Malta using wet and dry oxidation methods

Abstract

This study compares the determination of soil organic matter by three different Walkley and Black (WB) methods, and one Loss on Ignition (LOI) method. Four substrates, limestone, clay soil, carbonate sand and silica sand, were spiked with 3 % glucose, and then its recovery was attempted using the WB method with a reaction time of 1 min; 30 min; 30 min supplemented with heating at 150 oC and LOI set at 430 oC for 16 h. Additionally, the organic matter of 50 soils from the Maltese islands was determined by the methods described earlier and used to construct a conversion model between the methods. The study showed that the there is a significant difference in the results between the methods, with the reported organic matter content increasing with an increase in reaction time and temperature. Results from the LOI were significantly higher than those from the WB methods. In the glucose spiked experiment the quantity of recovered glucose was more accurate using the WB methods and the difference between LOI and WB increased as the clay and carbonate content in the sample increased. In the soil experiment this difference increased as the clay content increased and as the carbonate content decreased. Linear regression analysis between the various methods showed good correlation indicating that the methods developed could be used to transform values generated by LOI to the more accurate WB equivalent.