Syracuse

Comparison of the nicosulfuron herbicide degradation in soils under conventional and conservation agriculture

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Cueff, Sixtine | Alletto, Lionel | Mouquet, Déborah | Dumeny, Valérie | Goubard Delaunay, Yolaine | Benoit, Pierre | Pot, Valérie

Edité par CCSD -

International audience. Conservation agriculture (reduced soil tillage + cover crop + crop rotation) has been developed to reduce negative impacts on soil, especially soil erosion and runoff, generated by intensively-tilled soil in conventional agriculture. However, in conservation agriculture, weed control is more complicated and, in most cases, weeds are chemically controlled resulting in a more intensive use of herbicides. The environmental behaviour of these chemicals is, generally modified in conservation agriculture compared to conventional agriculture, mainly due to organic matter accumulation at the soil surface. Herbicide degradation can be either increased due to an enhanced microbial activity or decreased due to a reduced bioavailability caused by a greater sorption in surface horizons.The main objective was to compare the degradation of the nicosulfuron maize herbicide in soil samples collected from two sites located in south west France up to a depth of 90 cm. Both sites include contiguous plots under conservation and conventional agriculture. The soils were incubated during three months in laboratory conditions (in the dark at 28°C and at 80% of pF 2.5) with 14C-nicosulfuron. Water soluble fraction (CaCl2 extraction), adsorbed fraction (MeOH extraction), non-extractable residues (soil combustion) and mineralised fraction (14C-CO2 NaOH trapping) were quantified at 5 incubation times. Total mineralisation (CO2 NaOH trapping) and microbial biomass were measured and a qualitative analysis to detect metabolites presence was also performed.Microbial activity and biomass were the highest in the surface horizon of both conservation agriculture plots. However, in most cases, no significant differences were found regarding the degradation of nicosulfuron between the different agricultural systems. Soil depth significantly influenced nicosulfuron degradation which was lower in the deepest horizon of each site. Nicosulfuron distribution in the different fractions evolved during the incubation experiment for both sites: more mineralisation, less water soluble fraction and more bound residues were found with time.

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