Extractability and plant uptake of copper in contaminated coffee orchard soils as affected by different amendments

摘要

The effect of organic and inorganic amendments on the extractability and plant uptake of copper (Cu) was investigated in contaminated coffee orchard soils of the Kilimanjaro and Arusha regions of Tanzania. The soil was collected from 0-5 cm depth at a distance of 50 cm from coffee tree trunks. The total Cu concentration in the soil used was 250 mg kg(-1). Beans (Phaseolus vulgaris L.) and maize (Zea mays L.) were used as indicator crops and were grown in a greenhouse. The amendments used consisted of beringite, a modified aluminosilicate residue from coal mines, farmyard manure, banana compost, Albizia litter, and phosphate fertilizer. In general, the application of all amendments resulted in increased soil organic carbon (SOC) content and soil pH, which in consequence reduced both CaCl2-extractable Cu in soils and Cu concentration in both plant species. Beringite at all rates of application reduced the CaCl2-extractable Cu in soils and increased soil pH significantly, but the effect was most pronounced at an application rate of 5%. Similarly, the application of farmyard manure and banana compost at a rate of 10% significantly reduced the CaCl2-extractable Cu in soils. The increase in soil pH caused by the amendments was negatively correlated to both CaCl2-extractable Cu in soils and Cu concentration in plant tissue. However, the increasing concentration of CaCl2-extractable Cu in soils showed a positive correlation with Cu in plant tissue. Albizia litter at 10% incorporation rate significantly reduced the CaCl2-extractable Cu in soils. The application of P to maize reduced CaCl2-extractable Cu in soils, but the reduction in plant Cu was not significant. The results suggest that beringite, FYM and banana compost may be suitable amendments to reduce plant available Cu in soils and Cu uptake by plants, but their applicability and relative efficiency under field conditions need to be investigated.