PhD: Using organic matter to reduce pesticide leaching

Research challenges: Multiple interrelated processes determine the leaching of pesticides from fields. There is a complex interplay between sorption, which retains pesticides in soils, and biodegradation by microorganisms. Soil organic matter is central to this interplay. Soil organic matter quantity and quality determines sorption, supports biodegradation processes, and improves water holding content of soil, thereby reducing leaching of pesticide containing water. However, we currently insufficiently understand this interplay between specific organic matter types, specific soil types, and pesticide sorption and biodegradation. By investigating this interplay on lab, mesocosm, and field scale, we aim to attain a more fundamental understanding of the role that organic matter plays in pesticide sorption and biodegradation. This foundation is used to explore how soil amendment with different organic matter sources can reduce pesticide leaching.

Objectives and methodology: The main research question is how soil organic matter can be managed to reduce pesticide leaching by improving sorption and biodegradation in agricultural soils. The research approach aims to first understand the mechanisms by which different soil organic matters support sorption and biodegradation and establish the kinetics of these reactions.

Here, we particularly investigate the role of different soil organic matter qualities have on sorption and biodegradation processes. These results are subsequently upscaled in mesocosm experiments simulating leaching to compare the kinetics of pesticide sorption/biodegradation with leaching rates. Finally, organic matter amendments are tested to improve pesticide sorption and biodegradation based on an understanding of which soil organic matter qualities select for these processes. Together with soil management strategies, this final select of organic matter sources contributes to nature-based solutions for improving the natural capacity of soils to reduce pesticide leaching.