PhD Defence by Jeanne Vuaille

Jeanne Vuaille will defend her PhD thesis: 'Modelling the effect of selected agronomic practices on pesticide leaching to subsurface drain lines'

Summary

Intensive arable farming relies on pesticides, e.g. herbicides, insecticides, and fungicides. However, pesticide pollution in aquatic ecosystems is a threat towards freshwater biodiversity. Many fields in Western Europe have subsurface drainage systems that create a direct entry route of pesticides from fields to nearby streams, where the drains are discharged. Reducing pesticide transport to drains can therefore help mitigate environmental pollution from agriculture.

Pesticide leaching to drains is event driven in a complex interplay between weather (precipitation patterns in particular) and agronomic factors. This makes it difficult to assess the effects of, e.g. application timing, tillage types, and crop residues (mulch) using field trials. Hence, there is limited knowledge about the mitigation of pesticide leaching to drains. In all three studies of this thesis, the agro-hydrological model Daisy is used under Danish pedoclimatic conditions to understand and quantify the effect of specific changes in the agroecosystem description on pesticide leaching to drains.

The first study investigates whether field conditions and past and near-future weather can be predictors of the ecotoxicological risk of pesticide leaching to drains and help identify the safest application day. Based on Daisy simulations, a methodological approach enabling the use of information from the field and short-term weather forecast is tested for selecting safe pesticide application days. The second study assesses the effect of loosening wheel tracks, compacted due to the use of heavy machinery in agricultural fields, on pesticide leaching to drains. In the third study, a new mulch module is first introduced in Daisy to enable the modelling of the cropping system Conservation Agriculture (CA) and its effect on pesticide leaching to drains. The sensitivity of the simulated leaching towards a series of parameters is subsequently investigated.

Regarding the two first studies, the results show that optimizing pesticide application timing and loosening compacted wheel tracks may mitigate pesticide leaching to drains via drain-connected biopores and the risk for surface water organisms. In the third study, the results indicate that pesticide degradation in the mulch and surface layer in CA may be similar to that in the ploughing layer in ploughed fields and that leaching to drains is not higher under CA.

Further research is needed on modelling surface processes such as interception, retention, degradation, and wash-off of pesticides on the crop canopy and mulch. In general, more accurate and dedicated field measurements are needed to parameterize and calibrate models such as Daisy and to ensure that the modelled processes are properly described and understood.

Supervisor

Carsten Tilbæk Petersen
Co-supervisor: Per Abrahamsen

Assessment committee

Chair: Professor Nina Cedergreen

Senior Researcher Patricia Garnier, INRAE, Department of Environment and Agronomy, France
Senior Researcher Finn Plauborg, Aarhus University, Department of Agroecology, Denmark

There will be a small reception after the defence.