Water and pesticide transfers in undisturbed soil columns sampled from a Stagnic Luvisol and a Vermic Umbrisol both cultivated under conventional and conservation agriculture

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Cueff, Sixtine | Alletto, Lionel | Bourdat-Deschamps, Marjolaine | Benoit, Pierre | Pot, Valérie

Edité par CCSD ; Elsevier -

International audience. The main goals of conservation agriculture are to enhance soil fertility and to reduce soil degradation especially through erosion. However, conservation agriculture practices can exhibit a higher risk of contamination through vertical flows. The objectives of this study were to (i) characterise water and pesticide transfers in two different soils both managed under conventional and conservation agriculture and (ii) assess the effects of pesticide properties, soil type and agricultural system on pesticide fate. We studied the behaviour of two herbicides (nicosulfuron and mesotrione) and a molluscicide (metaldehyde) in percolation experiments in undisturbed soil columns. A series of two rain events (one with a high, the other with a low intensity) separated by a two-day flow interruption was applied three days after the pesticides and bromide application. Batch sorption coefficients, K-d, were also measured. While the Pesticides Properties Data Base (2020) indicated a decrease of sorption in the order mesotrione > metaldehyde > nicosulfuron, the measured K-d, decreased in the order mesotrione (2.3 +/- 1.4 L.kg(-1)) > nicosulfuron (0.7 +/- 0.4 L.kg(-1)) > metaldehyde (0.1 +/- 0.1 L.kg(-1)). We highlighted distinct behaviour of pesticide leaching depending mainly on soil type, agricultural practices and pesticide properties. For low degree of preferential flow, pesticide leaching can be related to the sorption properties of pesticides. Nicosulfuron and mesotrione delays are more pronounced under conservation management while metaldehyde always arrived with no delay. During the high intensity rain event, on one soil type, high degree of preferential flow masked sorption effect on leaching since every pesticide arrived at the same time as the tracer and amounted to up to 21% of pesticide recovery compared to 4% on the other soil type. Conservation agriculture was found to improve the vertical transfers of water and pesticides while, on one of the studied soil type, the presence of a low conductive plough pan significantly limits water drainage.

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