Chemical characterization of particle size fractions of calcareous soils from Hungary

However, calcareous soils cover more than 30% of the Earth's surface, research on the mechanisms of soil organic carbon (SOC) stabilization mostly focus on acidic soils. The SOC stabilization in calcareous soils is less frequently studied.

The present study investigates the carbon fractions with different stability in 29 Hungarian calcareous soil samples. The soil samples have varying organic (0.12 - 19.38 %) and inorganic (0.00 - 5.39 %) carbon content and represent different soil types (Cambisol, Arenosol, Gleysol, Solonchak, Regosol and Chernozem), land uses (forest, grassland, arable and marshy meadow) and depths (0-220 cm).

Physical fractionation was applied in order to represent the different organic matter fractions with varying stabilities. Six particle size fractions were separated during the fractionation: > 200 µm, 50-200 µm, 20-50 µm, 2-20 µm, 0-2 µm and particulate organic matter (> 200 µm). The mass, organic and inorganic carbon content and nitrogen content of the fractions were determined. The chemical characterisation of the fractions was determined using FT-IR spectroscopy. For the detection of relative changes in the spectra and the chemical characterization of the different particle size fractions, an aromaticity index (A_{1610 cm-1}/A_{2920 cm-1}) and relative absorbances (2920, 1740, 1680, 1610, 1525, 1270, 1160 and 1050 cm^-1) were calculated.

Principal component analysis showed great differences between the six particle size fractions in terms of their chemical properties (characteristic organic compounds, aromaticity and C/N ratio).

This research was funded by the SIC-SOC-DYN “Organic and inorganic carbon dynamic in calcareous soils” project of the 1st external Call within the EJP SOIL program, the National Research, Development and Innovation Fund, Hungary [Project N° 2019-2.14-ERA-NET-2022-00037 and FK 142936] and the French National Research Agency [Project N° ANR-22-SOIL-0003-01].