Effect of Land Use on Adsorption and Fractionation of Copper in High Andean Andisols

摘要

The presence of high concentrations of copper in soil generates risk of entry into food chain, causing adverse effects. To elucidate its behaviour and prevent potential toxic risks in High Andean soils of Rio "Las Piedras"sub-basin, we assessed availability, the different chemical species of this metal and the adsorption-desorption phenomena occurring in soil phases. We estimated the effect of land use change from forest to crop and pasture on physical, chemical properties, the soil organic matter quality, adsorption phenomena and speciation of copper. In these soils highlights strong acidity, presence of allophanes, high content of organic carbon, high cationic exchange capacity, sandy-loam texture and low bulk density. Organic matter quality was estimated from humification degree determined by different humification index. Crop use change improves quality and increased humified organic matter, opposite effect occurred in pasture. Adsorption phenomenon of copper was evaluated by Freundlich adsorption isotherms, K values were 266.81 (forest), 1103.06 (crop) and 691.19 (pasture); n values corresponded to 1.40, 1.19 and 1.27, denoting change in retention strength as adsorption capacity. The colloidal complex of these soils is not saturated with copper in the dose range used (50-300 mg kg~(-1)). Improvement in soil organic matter quality causes increase on copper adsorption process. The chemical speciation of copper in this High Andean soils reveals predominance of fraction bound to organic matter. The mobility factor increases on pasture soil but decreases on crop soil.