Differences in humic acids structure of various soil types studied by DRIFT spectroscopy

Abstract

Pavlů L., Mühlhanselová M. (2018): Differences in humic acids structure of various soil types studied by DRIFT spectroscopy. Soil & Water Res., 13: 29−35.The method of diffuse reflectance infrared spectroscopy (DRIFT) proved to be useful for studying the soil organic matter structure. The aim of this study was to compare DRIFT spectra of humic acids (HAs) separated from various soils and to identify their specific nature. Samples of agricultural soils (Dystric Cambisol, Haplic Chernozem, Greyic Phaeozem, and Haplic Luvisol) were collected from humic (A) horizons. Soil samples of reclaimed dumpsites (Haplic Technosol (molic) and (calcic)) were taken from the upper part of the soil profile. Samples of forest soils were collected from surface organic (H) horizons of Cambisols in spruce (Picea abies L. Karst.) and beech (Fagus silvatica L.) forests. The selected soil types differ in pH, carbon content, texture, and humus quality. An extraction of HAs was performed using a mixture of 0.5 M NaOH and 0.1 M Na 4 P 2 O 7 . The separated HAs were freeze-dried and analyzed using a DRIFT spectrometer (Thermo Nicolet Nexus) without KBr dilution. There were found differences in relative aromaticity among the agricultural soils HAs. The most aromatic character was observed in HAs from Chernozems and the least in Cambisols. Preservation of the natural structure of Chernozem HAs during the reclamation process was documented on the HAs spectra from Haplic Technosols (molic). By using the DRIFT spectra of HAs of forest H horizons, it is possible to identify the fragments of decomposed material (gymnosperms or angiosperms). HAs isolated from these horizons represent a certain interstage between lignin and the matured soil humic acids.

Comparison of soil organic matter composition under different land uses by DRIFT spectroscopy

“…The surface layer of the cropland soil differs from deeper layers, more pronounced peak can be seen around 3 000-2 800/cm and 1 000/cm, which represents higher contents of aliphatic components and polysaccharides chains of HAs. It could point to their lower maturity and stability (Pavlů and Mühlhanselová 2017). The intensity of the C=O group of ketones and amide group (shoulder in range 1 690-1 630/cm) decreases with soil depth.…”

“…structures (Piccolo 2001). Humic substances make up about 20% of the total of SOM and result from the decomposition and humification process of the SOM (Pavlů and Mühlhanselová 2017). They are often understood as relatively stable components of SOM, which are involved in the fixation and sequestration of carbon in the soil (Lal 2005).…”

“…Diffuse reflectance infrared fourier transform spectroscopy (DRIFT), as one of the types of infrared spectroscopy conventionally used for solid powder samples, is commonly used to analyse peat soil, composts, and the transformation of organic matter during composting within various stages (Haberhauer and Gerzabek 1999, Zaccheo et al 2002, Pavlů and Mühlhanselová 2017. The DRIFT spectra have been recognised as one of the spectroscopic techniques used to distinguish the fluctuation in the abundance of organic functional groups during decomposition and to identify the changes of SOM in the soil profile under different vegetation covers (Veum et al 2014).…”

Differences in organic matter quality, chemical and microbiological characteristics of two Phaeozems under natural and anthropic influence

“…Soil organic matter (SOM) consists of labile and stable substances, and the content of stable humic substances, resulting in the degradation and recombination processes, influences the stability of the soil structure and its characteristics (1,2).…”