Influence of cover crops on the presence and transfer of pesticides in agricultural soils

Details

Supervisors

Agnan, Yannick ; Vandevoorde, Noé

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement, à finalité spécialisée

Abstract

Pesticides are an indispensable component of modern agriculture, serving for pest control and yield enhancement. However, their extensive use presents a significant risk to human health and the environment due to their persistence in soils and water bodies. The objective of this thesis is to evaluate the influence of winter cover crops on the presence and transfer of pesticides in agricultural soils, through a three-month greenhouse experiment. This study examines three soil cover modalities: bare soil (control), a winter cash crop (winter spelt), and a winter catch crop (multi-species cover crop). A total of 19 pesticides, encompassing a range of physicochemical properties, were applied, and their concentrations were monitored over time. The results demonstrate that pesticides exhibit distinct distributions, with persistent and hydrophobic molecules exhibiting a prevalence in soil, while soluble and volatile ones are prevalent in the soil solution. A temporal monitoring revealed the remanence of persistent molecules over time. The analysis of the control samples exhibited a range of mass reductions among different molecules, with a few unexpected increases that may be attributed to sampling biases. A comparison of the modalities reveals that only winter spelt (monospecific cover) significantly reduces the pesticide content. This reduction can be attributed to the biomass density of the spelt, which was three times greater than that of the multi-species mix. In the experimental conditions, the density of the cover crop was found to be a more influential factor than its diversity in reducing pesticide residues. These findings indicate that high-biomass cover crops can play a crucial role in mitigating pesticide leaching. To achieve the greatest efficacy, it is recommended that cover crops be sown as soon as possible after the previous crop harvest, to ensure adequate soil coverage before the onset of autumn and winter rainfall. To gain a more comprehensive understanding of the efficacy of diverse cover crop species and densities, as well as to enhance sustainable agricultural practices, it is necessary to conduct longer and larger-scale field trials. Moreover, a coupled study of soil geochemistry and hydrology is required to gain a deeper understanding of pesticide dynamics.