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Water and pesticides transfers in undisturbed soil columns sampled in conservation and conventional agriculture
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Edité par CCSD -
International audience. Conservation agriculture (reduced/no tillage + cover crop + crop rotation) improves soil structure by (i) maintaining organic matter at the soil surface, (ii) enhancing soil biology and (iii) preserving biopores (e.g. root and earthworm burrows). In most cases, this leads to a decrease in soil erosion and runoff and to an increase in soil water infiltration through the presence of well-connected macropores. Such hydraulic dynamic could lead to an increase of vertical leaching of pesticides through preferential pathways. Mulch at the soil surface could however counterbalance this by pesticide interception that delays their leaching through the soil.In this laboratory experiments, the effects of soil management, conventional vs. conservation agriculture, on three pesticides leaching (metaldehyde, nicosulfuron and mesotrione) were studied. The two field sites, located in South West of France, include two contiguous plots under conservation and conventional agriculture. Undisturbed soil columns were collected from the surface horizon of the four plots. A series of high and low intensities rainfall events was applied two days after conservative bromide anion and pesticides application. The breakthrough curves were monitored during the three weeks experiment. Pesticides concentrations were measured by LC-MS-MS and bromide concentration was measured with a specific electrode. At the end of the experiment, analysis of pesticides was performed in 4 soil layers and in the mulch.On the first site, metaldehyde arrived at the same time as bromide whereas the other pesticides were delayed. Mesotrione was clearly more delayed in conservation agriculture. Most of applied nicosulfuron was collected in leachates but lower quantities were recovered for metaldehyde and mesotrione. After columns slicing, both nicosulfuron and mesotrione had the highest concentration in the surface layer. The concentrations decreased with depth. On the second site, all three pesticides arrived at the same time as bromide whatever the practices, suggesting strong preferential flow.
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