Abstract
Agricultural soil use does not only affect the amount of soil organic matter, but also the molecular composition of humic (HAs) and fulvic acids (FAs). Changed hydrothermal conditions and composition of the incoming plant residues are reflected in the rate of humification and its products. The objective of this study was to compare the molecular composition of HAs and FAs isolated from Eutric Albic Stagnic Histic Retisol (Loamic), two Eutric Albic Retisols (Loamic)—mature and arable. Plots of mature Retisols are located at a middle taiga (Komi Republic, Russia) in a bilberry-green-moss birch-spruce forest. The plot of Retisols arable is located in the fields of the Syktyvkar state farm, which is 3.3 km northeast of mature Retisol plots. The development period is about 40 years, it is sowed with a pea-oat mixture. The results obtained indicate that soil reclamation essentially increases the proportion of aromatic components and decreases the content of carboxyl and ester groups in the humic substance (HS) structure. An increased extent of hydromorphism of Retisols leads to the enrichment of HS with aliphatic fragments.
Highlights
The carbon cycle disequilibrium is a key challenge to humanity in the 21st century
When comparing the molecular structure of HAs in soils with different degrees of hydromorphism, it should be noted that HAs isolated from Eutric Albic Retisol (Loamic) have a higher content of aromatic fragments compared to HAs from Eutric Albic Stagnic Histic Retisol (Loamic)
An increase in the relative content of oxygen-containing functional groups (–COOH, CAr=O and –C=O) in HA molecules was noted during the transition from the O to OEL horizons in Eutric Albic Retisol (Loamic)
Summary
The carbon cycle disequilibrium is a key challenge to humanity in the 21st century. An increased concentration of CO2 in the atmosphere and dehumidification of soils are interrelated phenomena and the most typical attributes of anthropogenic disturbances in the global carbon cycle. The SOC increment rates and limits depend not merely on the quantity and quality of the incoming organic matter, and on the stabilization of organic components in the soil [1]. Several articles have questioned the role and even existence of soil humic substances (HS) as a distinct entity in SOM [2]. They are dealt with questions of SOM as a continuum of degradation reactions by unspecified processes from the original biomass inputs to carboxylic acids, and eventually to carbon dioxide without the formation of new classes of compounds along the way
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