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Sorption of pesticides in soil from grassed and forested buffer zones: the role of organic matter

Abstract : Grassed and forested buffer zones can reduce pesticides tranfer by surface runoff from cropped areas to rivers at the scale of rural watersheds. Their effectiveness and their functioning as depolluting systems is due to several soil phenomena, of physical (infiltration), chemical (sorption) and biological (degradation) origins. The part of each phenomenon is however not quantified and may significatively vary according to the season and the site specificities At relatively short terms (years), some soil properties are modified by the change in land-use consecutively to the implantation of a buffer zone : a soil intensively cropped turning to permanent grassland or to forest. Some of these modifications will play a determinant role in the fate of the pesticides trapped within the filter strips. The increase of organic matter with a large input of non humified residues is one of the first modification occurring in the topsoil. This study aimed to quantify the role of organic matter changes on the sorption of two herbicides, lsoproturon and Diflufenican and Isopropylaniline, a potential metabolite of Isoproturon. A soil originating from the same site, but with three contrasted land-uses : grassland, forest and maize-wheat crop rotation has been considered. Several soil horizons were distinguished and for the top layers, soil size fractions were isolated by physical fractionation techniques in order to separate particulate organic matter (POM) from fine organomineral fractions < 50 µm. Coarse plant debris at the soil surface were also recovered and studied. On each soil layer and soil size fraction, we have characterized the sorption and desorption of the three molecules using 14C labelling techniques. Sorption of the 3 compounds is significatively greater in the grassed and forested soils compared to the cropped soil. Isoproturon dissipates faster in the grasssed topsoil, compared to the forest soil due to more active degradation. In both soils, dissipation is explained by the formation of the metabolite isopropylaniline which was irreversibly sorbed. The coupling between isoproturon degradation and the formation of non extractable residues is particularly important in the grassed strip litter. The results obtained in forest and grass litter layer suggests that the amount and the nature of organic materials are two important factors in the regulation of these coupling. Significant differences in sorption coefficients Koc were observed between the surface horizons and suggested that the nature of organic matter was involved. Particulate organic matter showed high sorption capacities and may play an important role in the overall retention capacity of the surface soil layers. The informations obtained on the soil size separates by FT-IR and 13C NMR and wettability measurements demonstrat that the aromaticity and the hydrophocity of POM were important regulating parameters of the sorption capacities. The specific area of the soil size fractions was also an important issue as well as the accessibility of sorption sites within the particles themselves. Comparing the sorption behaviour on the different soil size fractions to the behaviour in the whole soils, show that the accessibility of organic matter in the soil agregates may explain the differences observed under the three different soil use, and intefere with the influence of soil organic composition.
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Submitted on : Wednesday, April 27, 2005 - 8:00:00 AM
Last modification on : Wednesday, April 27, 2005 - 8:00:00 AM
Long-term archiving on: : Thursday, September 30, 2010 - 6:29:39 PM


  • HAL Id : pastel-00001214, version 1



Ismael Madrigal - Monarrez. Sorption of pesticides in soil from grassed and forested buffer zones: the role of organic matter. Sciences of the Universe [physics]. INAPG (AgroParisTech), 2004. English. ⟨NNT : 2004INAP0016⟩. ⟨pastel-00001214⟩



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