Assessing the effects of grinding on soil's thermogravimetric records: implications for carbon, nitrogen, and soil structure analysis

Abstract

Soil structure is a key factor influencing its ecosystem functions. Previous research has shown a close correlation between mass losses obtained using thermogravimetry (TG) and soil properties such as the content of organic carbon and nitrogen, which has consequently enabled the determination of several relationships among obtained mass losses. The high degree of correlation has been explained, among other factors, as a result of the intact structure of the investigated soils. However, this hypothesis has never been experimentally tested. Therefore, this study investigates the effects of mild grinding, which primarily affects soil particles larger than 250 µm, on soil's TG records to determine its impact on the analysis of carbon, nitrogen, and relationship between mass losses. Soil samples from the island of Santorini, contaminated by heavy metals and dust from traffic, were analyzed with and without grinding using TG. Grinding affected the TG records across the entire temperature range, with the most significant decrease observed below 200 oC, where moisture evaporates. A mild increase was observed in the temperature range, where soil organic matter degrades. The determination of soil carbon and nitrogen content was only slightly impacted, which was explained as a result of only a small impact of grinding on soil microaggregates and organo-clay complexes. Despite these minor changes, as revealed by autocorrelation analysis, grinding significantly affected the relationships between mass losses. We conclude that soil grinding in TG analysis can be recommended for basic soil parameter analysis or contaminated soils due to improved homogeneity. However, it may compromise advanced analyses due to shifts in correlations between mass losses corresponding to the relationships between particular soil components.