The chemical structure of the organic matter of typical chernozems of various farming technologies

The transition to sustainable agriculture involves the adoption of soil-saving technologies, such as no-till (NT), as an alternative to conventional tillage (CT). The introduction of NT fundamentally alters the dynamics of plant residue input and decomposition; however, its effects on the molecular composition of soil organic matter (SOM) remain insufficiently studied. This study aimed to conduct a comparative assessment of the influence of NT and CT on the chemical structure of SOM in typical chernozems. Soil samples were collected from 0–10 cm and 10–20 cm depths in the 8-year field experiment with a four-course grain crop rotation under NT and CT management. Standard soil chemical properties (pH, available phosphorus and potassium, total nitrogen, and organic carbon) were analyzed. The chemical structure of SOM was characterized using Fourier-transform infrared (FTIR) spectroscopy and analytical pyrolysis. The molecular structure of SOM demonstrated the most pronounced dependence on the tillage practice compared to all other measured properties. The transformation under NT was characterized by the accumulation of carbohydrates and products of their microbial metabolism. In contrast, CT led to the dominance of recalcitrant compounds within the passive pool, which are not involved in active microbial transformation. Correlation analysis revealed that the trends of accumulation of organic carbon under NT is associated with the increased contribution of carbohydrates and phenolic compounds to the SOM composition.