Widespread Occurrence of Pesticides in Organically Managed Agricultural Soils—the Ghost of a Conventional Agricultural Past?

Summary

This comprehensive field screening of 100 European agricultural fields demonstrates that pesticide residues are ubiquitous in both conventional and organic soils, though conventional fields showed nine times higher concentrations and twice as many residue types. Pesticide burden declined progressively with years under organic management but remained detectable even after two decades, and was significantly negatively associated with beneficial soil microbial communities, particularly arbuscular mycorrhizal fungi. The findings suggest that pesticide legacy effects represent a hidden but meaningful constraint on soil biological function in agroecosystems.

UK applicability

These findings are directly applicable to UK agriculture given similar soil climates and farming histories. The persistence of pesticide residues in UK organic soils following conversion from conventional management implies that soil health benefits from organic certification may be initially constrained by historical pesticide loading, with implications for transition period expectations and soil remediation strategies.

Key measures

Number and concentration of pesticide residues (46 compounds screened: 16 herbicides, 8 herbicide transformation products, 17 fungicides, 7 insecticides); microbial biomass; abundance of arbuscular mycorrhizal fungi; duration of organic management

Outcomes reported

The study screened 100 fields under organic and conventional management for 46 pesticides and measured pesticide residue occurrence, abundance, and effects on soil microbial biomass and arbuscular mycorrhizal fungi. Pesticide residues were detected in all sites including 40 organic fields, with concentrations and diversity declining over time under organic management but persisting even after 20 years.

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