The effect of a soil conditioner on the detoxification of oil-contaminated soils and the quality of their organic matter

Goal. To investigate the effect of a soil conditioner on the qualitative composition of organic matter in oil-contaminated soils. Methods. Field methods — for soil sampling; laboratory methods — for analyzing soil samples; electronic spectroscopy in the ultraviolet and visible ranges — for analyzing the humic substances obtained; mathematical and statistical methods — for processing experimental data. Results. The study was conducted in 2024 as a small-plot field experiment on the grounds of the research farm of the National Scientific Center «Institute of Soil Science and Agrochemistry named after O.N. Sokolovskyi» (vil. Korotych, Kharkiv district, Kharkiv oblast) in the Left-Bank Forest-Steppe region. The soil of the experimental plot was a heavy loamy podzolized chornozem on loess-like loam. The experimental treatments involved simulating soil contamination with crude oil at two levels: moderate — 6.4 L/m2 — and high — 25.6 L/m2 — with the application of a soil conditioner. To analyze the humic substances obtained after group fractionation of soil organic matter, the method of electronic spectroscopy in the ultraviolet and visible ranges (200–600 nm) was used. Soil respiration rates were determined using non-stationary respiration chambers and a portable analytical instrument — the Testo 535 gas analyzer. A 25% decrease in the content of exchangeable cations in the soil-adsorption complex of contaminated heavy loamy podzolized chornozem was observed compared to that of uncontaminated soil. It should be noted that the nutrient status of crops has deteriorated: the content of mobile nitrogen and phosphorus compounds decreased by 25%, and that of mobile potassium compounds by 36%. The results of spectroscopic analysis showed that the application of a soil conditioner contributed to an increase in the activity of organic matter transformation processes in contaminated heavy loamy podzolized chornozem. An improvement in the quality of soil organic matter was observed, which was associated with an increase in the size of micellar particles of chornozem humic substances due to active intermolecular aggregation of newly formed humic acids and the formation of large and stable humic micelle-like (supramolecular) aggregates. Conclusions. It was established that the application of an organic soil conditioner to oil-contaminated heavy loamy podzolized chornozem activated the processes of soil organic matter transformation and intensified humification through the formation of humic acids.