Retention of copper, cadmium and zinc in soil and its textural fractions influenced by long-term field management

The present study investigated the impact of long-term soil management on the metal retention capacity of soil. We examined the sorption behaviour of Cu, Cd and Zn in soils and in the various particle-size fractions of these soils, which had been amended with farmyard manure, mineral fertilizers or were fallow for 38 years in a long-term field experiment. The soils investigated contained different amounts and origins of organic matter and differed in soil pH, but the mineral phase showed less response to the different soil managements. Batch adsorption and desorption experiments as well as a sequential fractionation schema, which defines seven geochemical fractions, were used to investigate the retention properties of soil. Sequential extraction was conducted with original as well as with metal-spiked soils. Results showed that amounts of Cu, Cd and Zn retained differed by a factor of more than 3 among the treatments in the long-term field experiment, when a massive concentration of metal was added to soil. An increased sorption on smaller particle size fractions occurred (clay > silt > fine sand >= coarse sand) due to the larger surface area as well as the greater carbon content in the smaller fractions. Soil sorption behaviour in another long-term field experiment was estimated based on the present particle-sorption data. Differences in the sorption behaviour were related to differences in soil mineralogy and amounts of Fe- and Mn-oxides. Fractionation of the original and the metal-spiked soil underlined the contribution of organic matter to sorption capacity (sequence: Cu > Cd > Zn). Different organic matter contents and a different soil pH considerably changed the amounts of metals in the defined geochemical fractions. Freshly added Cu, Cd and Zn ions were found mainly in more mobile fractions. In contrast, metals in non-spiked soils appeared in less-mobile fractions reflecting their long-term sorption behaviour.