Using a Rock-Eval device for thermal oxidative analysis of calcareous soils with low organic carbon content: A technical note

Abstract

Quantifying soil organic and inorganic carbon with a high degree of accuracy is an area of growing scientific interest. There are many methods available for quantifying soil organic carbon (SOC) and soil inorganic carbon (SIC), either separately or simultaneously. Some of these methods present limitations and uncertainties for the quantification of these two forms of soil carbon, particularly in calcareous soils with low SOC contents. Rock-Eval (RE) thermal analysis, which emerged as a major tool in soil science over the last few decades, has its advantages over other analytical methods, but it also has its limitations, particularly for studying soils with low SOC contents. Here, we propose a new thermal oxidative method with the REdevice to quantify low levels of SOC in calcareous soils: Oxypure. We analyzed soils using both the standard protocol of RE thermal analysis (RE650) and dry combustion using an elemental analyzer (EA) and compared them with the Oxypure method. Our results show that the RE650 protocol is inadequate for studying calcareous soils with low SOC content. Compared to the reference method EA, the Oxypure method is more suitable for quantifying SIC and SOC in calcareous soils with low SOC contents. This study also shows that SOC can be characterized from a combined C–CO₂ thermogram obtained using the Oxypure method. Overall, this study has demonstrated that the Oxypure method is more suitable than the RE650 protocol for studying calcareous soils with low SOC content, and we strongly recommend this method for these particular soils.