Influence of long-term application of agrochemicals on the dynamics of soil organic matter and acidity

Abstract

The findings of a long-term lysimetric experiment (1987–2024) on the study of the influence of long-term systematic application of agrochemicals on the dynamics of organic matter and acidity in leached chernozem are discussed. The study followed a scheme that included two factors: the level of mineral nutrition (control, moderate, and high rates of NPK) and the application of plant protection agents (PPA). The analysis revealed that the level of chemicalization had a pronounced influence on the key soil fertility indices: humus and acidity. In the variants without any fertilizer application, significant degradation of the humus horizon was observed, with losses of up to 22% in the active arable layer of 0–20 cm, while the changes in the subsoil layer (21–40 cm) were minimal. The application of moderate fertilizer rates allowed for the stabilization of humus content, and the combination of high rates with PPAs ensured its increase by up to 8% in the arable horizon due to increase and preservation of total biomass. Concurrently, a clear trend toward progressive soil acidification directly dependent on the level of anthropogenic impact was found. The greatest acidification (16% decrease in pH and a 56% increase in hydrolytic acidity) was revealed with high fertilizer rates without PPAs which was associated with nitrification processes and the removal of exchangeable bases. The application of PPAs had a moderate mitigating effect reducing the rate of acidification. The main conclusion is the necessity of a differentiated approach to soil fertility management: for humus stabilization with minimal acidification, moderate fertilizer rates in combination with PPAs are advised, whereas in intensive systems with high rates, systematic acidity control through liming and constant agrochemical monitoring is mandatory.