Over 50 years of a field experiment on cropping systems in Bałcyny, Poland: Assessing pesticide residues in soil and crops from the perspective of their field application history

Many agricultural problems can be illustrated and solved through long-term field experiments. Since 1967, an experiment has been conducted in Bałcyny, Poland, to compare continuous cropping with growing crops in crop rotation. The experiment also provides information on the history of chemical crop protection, which may have influenced soil and crop contamination with pesticide residues. In this study, fields of winter rye in continuous cropping (CC_rye) and a 5–6-field crop rotation (CR_rye) were used as an example to investigate the occurrence of pesticides in soil and grain in the context of previous use of chemical crop protection products. Two levels of crop protection were also examined: herbicide (since the 1972/73 growing season) and fungicide (since 1982/83) application (HF) and control treatment (CT; no herbicides since 1972/73, no fungicides since 1982/83). Insecticides were used only when absolutely necessary. Between 1967 and 2019, 58 different active substances were applied to the fields selected for this study. Soil and grain samples collected in 2019 after rye harvest were analyzed for the presence of 441 and 496 different substances, respectively. Only DDT and its metabolites were detected in soil, even though DDT was not applied to the fields after 1967. The concentration of ΣDDT (sum of all metabolites and isomers) ranged from 038 to 130 µg kg^–1 soil and exceeded the limit set in Poland (120 µg kg^–1) under CR_rye-HF treatment. In winter rye grain, no pesticide residues were found. The results show that long-term rational use of less persistent pesticides does not lead to contamination of the soil or the test cereal grain, but DDT continues to threaten the environment five decades after its probable last use. The study points to the value of comprehensive long-term recording for providing a retrospective assessment of pesticide exposure. Long-term field experiments facilitate this approach.