The effect of hydrogen on the chernozem redox properties and humus in model experiments

Abstract

The purpose of the study was to identify changes in the redox environment and a range of chernozem humus characteristics under the influence of hydrogen flux.

Venue and time. The model experiments were carried out in the laboratory of the Faculty of Soil Science of Lomonosov Moscow State University. The experiments used samples of the upper arable horizons of ordinary (Voronezh region) and leached (Lipetsk region) chernozem, selected in the background areas of research sites located beyond the  hydrogen flux.   

Methods. The total organic carbon content was determined by the dichromate oxidation method, dissolved organic carbon in soil solution was measured by catalytic oxidation with a TOC analyzer with an IR detector, and the values of the redox potential and the pH of the aqueous suspensions were determined potentiometrically. The isolation and purification of humic acid (HA) preparations was carried out by the method recommended by the International Humic Substances Society. The HA elemental composition was determined using a Vario EL III elemental analyzer. Measurement of the element content in soil solution wad carried out using the ICP-OES method on an Agilent 5110 optical emission spectrometer. The iron content of non-silicate compounds was measured in a Mehra–Jackson extract, and the iron of weakly crystallized compounds in the composition of non-silicate compounds was  measured in a Tamm extract. The NMR ¹H and NMR ¹³C spectra of HA were obtained using a Bruker AMX-400 NMR spectrometer.

Results. In a series of model experiments it was shown that under the influence of hydrogen flux in chernozem redox conditions changed dramatically, the integral indicator of such changes being a decrease in the soil redox potential to extremely low values, while there a slight decrease in the actual acidity was observed. In such conditions, humus was transformed. According to the ¹³C NMR spectra, it can be concluded that soiln waterlogging had little effect on the fragmented composition of humic acids in chernozem, whereas the incoming hydrogen ensures the destruction of the peripheral part of humic molecules without destroying the aromatic clusters. Under conditions of the model experiment, in the presence of a hydrogen flux in the soil the content of citrate-soluble and oxalate-soluble iron increased, indicating the intensification of the gley process. In addition, the processes of removing organic matter from the soil into the soil solution intensified, and the increased. aluminum concentration in it indicated the likely destruction of the crystalline lattices of aluminosilicates, which are part of the solid phase of the soil.