Carbon measurement of peat soils: Significant differences between two grinding methods

Peat soils are estimated to store over 500 Gt of carbon (Yu, 2012), and their ongoing sequestration plays a pivotal role in mitigating climate change. However, improved measurements of peat carbon content are necessary due to inherent differences between peat soil environments. Emphasis has been placed on accurately measuring carbon content in peat samples to understand carbon dynamics and estimate their stores. A protocol developed by Chambers et al., (2011) requires the mechanical grinding of peat samples before elemental analysis. Yet, there has been a lack of investigations into how different grinding methods may directly affect carbon measurements in peat soils.

Previous studies (Abulikemu, 2023; Markert, 1995; Pulleman et al., 2021; Siang, 2010) have investigated the influence of grinding on organic materials. Results indicate differences in the extent of carbon alteration and release depending on the grinding method employed. The shock and abrasive forces of ball mill grinding generate mechanochemical alterations in organic matter (Abulikemu, 2023), whilst pestle and mortar grinding relies on friction and pressure (Markert, 1995). Energy generated during ball mill grinding has been linked to higher oxidation and pyrolytic reactions (Abulikemu, 2023; Siang, 2010).

Given these findings, the choice of grinding method may artificially alter the carbon in peat soils, providing misleading measurements of carbon content and accumulation rates. This research examines the influence of two commonly utilised grinding methods, ball mill and pestle and mortar. Four peat samples were ground using both methods and measured using an elemental analyser. Seven subsamples from each ground sample were measured separately (Total = 56). The uppermost sample, from acrotelmic peat, showed no significant differences (p > 0.05), whereas the three lower, more decomposed, catotelmic peat, suggest high significance (p < 0.001). In all cases, pestle and mortar ground samples displayed higher carbon values than their ball mill counterparts.

These findings align with previous studies, suggesting that the choice of grinding method may influence the carbon content of organic material (Abulikemu, 2023; Pulleman et al., 2021; Siang, 2010). Thus, concerns are raised here regarding the influence of grinding and the comparability of results.

 

 

 

 

 

 

Abulikemu, G., 2023. Role of grinding method on granular activated carbon characteristics.

Chambers, F.M., Beilman, D.W., Yu, Z., 2011. Methods for determining peat humification and for quantifying peat bulk density, organic matter and carbon content for palaeostudies of climate and peatland carbon dynamics. Mires Peat 7, 1–10.

Markert, B., 1995. Sample preparation (cleaning, drying, homogenization) for trace element analysis in plant matrices. Sci. Total Environ., State of the Art of Trace Element Determinations in Plant Matrices 176, 45–61. https://doi.org/10.1016/0048-9697(95)04829-4

Pulleman, M., Wills, S., Creamer, R., Dick, R., Ferguson, R., Hooper, D., Williams, C., Margenot, A.J., 2021. Soil mass and grind size used for sample homogenization strongly affect permanganate-oxidizable carbon (POXC) values, with implications for its use as a national soil health indicator. Geoderma 383, 114742. https://doi.org/10.1016/j.geoderma.2020.114742

Siang, K.S.Q., 2010. The rates of formation of carbon and gases from high energy ball milling of organic compounds.

Yu, Z.C., 2012. Northern peatland carbon stocks and dynamics: a review. Biogeosciences 9, 4071–4085.