Characterization of organic matter content of Hungarian agricultural soils

Abstract

Humic substances have proved to be very important fractions in soils, playing a key role especially in agricultural soil and influencing chemical and physical soil properties. Spectroscopic methods are widely used to identify the quality of soil humic substances. In this study, 16 soil samples were selected from the Soil Bank of the Soil Science Laboratory at Szent István University, Gödöllő. The samples were extracted using the Hot Water Percolation (HWP) method and the amount of dissolved organic carbon (DOC) in each fraction was measured. The kinetics of the DOC extraction process with the HWP method was estimated. The Ultraviolet Visible (UV-VIS) technique was used to characterize the properties of HWP-dissolved organic carbon (HWP-DOC), measuring absorbance at 200–700 nm. Among the humification parameters, the absorbance ratios at 254 and 365 nm (E2/E3) and 465 and 665 nm (E4/E6), the specific UV absorbance (SUVA) and the UV absorbance ratio index (URI) were estimated. The K factor (humus stability coefficient) and E2/E3 and E4/E6 in NaOH and NaF extracts were also measured. The properties of HWP-DOC were similar in most of the soil samples. There was a good correlation between the content of HWP-DOC and the absorbance at 254 nm. URI, SUVA, E2/E3 and E4/E6 indicated that most of the HWP-DOC in the samples consisted of fulvic acid components with greater activity, simpler structure and low molecular weight.

Extracted samples and in situ soil investigations to assess the effects of different land use and tillage management practices on soil organic matter composition

“…A lower E 4 :E 6 ratio implies a higher molecular weight (MW) and a higher degree of condensation of the aromatic rings, which is independent of humic substance concentrations but is indicative of the different natural OM fractions of humic substances acquired from diverse sources (Chen et al, 1977). The E 2 :E 3 ratio reflects the average MW (Nadi et al, 2012) and considers aromaticity measurement. Its value is inversely proportional to aromaticity and MW (Chen et al, 1977).…”

Dilution Effect on the Investigation of Soil Organic Matter Quality in UV-VIS Spectra

“…Some, also commonly accepted methods (especially in the Eastern European region) are the E4/6 [465/665 nm] or E2/3 [250/365 nm] ratio (CHEN et al 1977;NADI et al 2012;SARLAKI et al 2020). These measurement methods are based on the spectral analysis of organic matter extracts.…”