Influence of different land uses on soils organic matter composition from North Eastern part of Romania based on DRIFT spectra

This study addresses a topical issue, which is a particularly important indicator in assessing the evolutionary trends of the global climate system, namely the storage of carbon in the soil in the form of organic matter. The aim of the research is to estimate and characterize the organic matter from soils with different types of uses and depths located in the North-East Region of Romania, which occupies an area of 36,850 km², characterized by a special natural complexity that has undergone recent structural changes. Soil samples from organic and mineral horizons located at different depths were analyzed. The influence of different land use on the content and chemical composition of organic matter in soils in a topsoil located on the North South was analyzed. The analysis includes a number of 200 soil samples collected from seven different sites (Humor, Pipirig, Vanatori, Tg Neamt, Timisesti, Raducaneni and Munteni) including forest, pastures, arable land, orchards, whether or not subject to specific traditional amendments. Quantitative determination was performed by dry combustion using the combination of equipment: Analytik Jena multi N / C 2100 analyzer and HT 1300 solids module, while for the chemical composition of organic matter the Fourier transform infrared spectroscopy is used (Vertex 70 Bruker), using DRIFT as a sample preparation technique. The amount and chemical composition of organic matter, as well as the location and properties of the soil, have had a strong influence on DRIFT spectra, which are sensitive to the degree of decomposition of organic matter. Differences in absorbance intensity for several spectral bands indicated a higher abundance of recent residues, phenolic-OH, aliphatic and carbohydrate compounds in soils under agricultural use compared to the dominant presence of amide and aromatic groups, carboxylic acids and their salts, C = C bonds in forest soils occupied by deciduous, mixed or coniferous vegetation. Drift spectra have been associated with a number of physicochemical attributes of the soil, such as land cover type, parent material, depth and bulk density, pH, texture, etc. The main conclusion from the regional study indicates that the information recorded in the DRIFT spectra of soils combines the amount and chemical composition of soil organic matter with soil properties highlighting the potential use of this information to assess the state of organic matter degradation stored in the soils of the North East region of Romania.

Keywords: soil organic matter, FTIR, functional groups, Romania, soil composition

"This work was supported by a grant of the "Alexandru Ioan Cuza" University of Iasi, within the Research Grants program, Grant UAIC, code GI-UAIC-2021-12".