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Impact of pig slurry and green waste compost application on heavy metal exchangeable fractions in tropical soils

Doelsch E., Masion A., Moussard G.D., Chevassus-Rosset C., Wojciechowicz O.. 2010. Geoderma, 155 (3-4) : p. 390-400.

DOI: 10.1016/j.geoderma.2009.12.024

Six soil/waste samples were incubated at 28 °C under standard conditions to assess the impact of organic waste applications on heavy metal (HM) exchangeable fractions. The three studied soils are representative of the pedological diversity that prevails in Réunion and characterized by high natural total Cr, Cu, Ni and Zn concentrations. For organic waste, we tested two products that differed in their chemical composition, physical state and different HM contents, i.e. pig slurry (PS) and green waste compost (CT), which were incorporated at dosages consistent with the actual agricultural setting: 350 and 1000 kgN ha?1 (subsequently called 350 and 1000). Variations in pH and electrical conductivity (EC) were monitored during incubation, while also measuring carbon mineralization and HM exchangeable fractions (Cr, Cu, Ni and Zn). The physicochemical parameter variation patterns were not identical in the three soils. The greatest variations were noted in the cambisol: pH reduction and EC increase. Conversely, in the andosol, there were only slight variations in pH and EC during incubation. The C-CO2 quantities detected were derived from PS mineralization, and were always higher than those from the mineralization of CT, irrespective of the soil considered, and C mineralization was proportional to the initial quantity of incorporated waste (350 vs 1000). We explained the difference in the andosol mineralization coefficient between the 350 and 1000 dosages as being the result of an interaction between the organic constituents and the pseudo-cristallized aluminosilicates from the soil (allophane and/or imogolite), which limited degradation of the incorporated organic matter (OM). Despite organic waste mineralization, the pH variations recorded during the incubations and the increased salinity, we did not detect any increase in the HM exchangeable fractions, but instead noted a decrease in the Cu exchangeable fraction (soil+PS incubation), which could be explained by complexation of this element by the OM.

Mots-clés : déchet agricole; recyclage des déchets; engrais; Élément métallique; métal lourd; sol volcanique; sol tropical; pollution du sol; pollution par l'agriculture; compost; lisier; réunion; france

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