Organic waste amendments effect on zinc fractions of two soils

Organic soil amendments can ameliorate metal toxicity to plants by redistributing metals to less available fractions. The objective of this study was to determine the effects of organic amendments on Zn distribution among soil fractions. Two soils (fine-textured and coarse-textured) were amended with five organic waste materials (some of which contained Zn) or commercial humic acid with and without 400 mg kg(-1) Zn, incubated, and fractionated using a sequential extraction technique, Where no Zn was added most of the metals were in the residual fraction. Commercial compost, poultry litter, and industrial sewage sludge increased Zn in the exchangeable (EXC), organic (OM), and manganese oxide (MnOx) fractions due to Zn in the materials, Spent mushroom compost (SMC) redistributed Zn from the EXC fraction to the MnOx fraction for the coarse-textured soil. Where Zn was added, most of the metal was in the EXC and OM fractions. The SMC and humic acid lowered Zn in the EXC fraction and increased Zn in the other fractions. Effects of the organic materials on Zn in soil fractions were more evident for the sandy soil dominated by quartz in the clay than for the finer-textured soil dominated by kaolinite in the clay-size fraction. It was concluded that organic materials high in Zn can increase Zn in the EXC, OM, and MnOx fractions where the soil is not contaminated and others such as SMC and HA can lower the potential availability of Zn in contaminated soils by redistributing it from the EXC to less soluble fractions.