Fractionation and Speciation of Copper and Zinc in Poultry Litter Amended Soil

Authors: Candice O. Freeman, M.R. Reddy, and W.A.R.N. Fernando

ABSTRACT

North Carolina is the 5^th largest broiler-producing state in the United States. A common method of disposing the broiler litter is using it as an organic fertilizer, to improve soil fertility.  Long term disposal of poultry litter can potentially lead to heavy metal accumulation in the soil which may cause phytotoxicity.  The objectives of this study were to fractionate Cu and Zn, determine the impact of pH on Cu and Zn fractions, and to determine the speciation of Cu and Zn in the soil.  A Toccoa Sandy Loam (Coarse-loamy, mixed active, nonacid, thermic Typic Udifluvents), was collected from a field in Wilkes County, North Carolina.  The field was amended with poultry litter for over 20 years.  Soil samples were prepared using standard methods.  The pH of the original soil and the adjusted sub-sample of the soil is 4.7 and 6.3, respectively. A modified sequential extraction procedure was used to determine the distribution of copper and zinc among exchangeable, carbonate bound, organically bound, and the fraction associated with lattice structure of minerals.  The soil with the higher pH showed the highest amount of copper in the oxidizable fraction.  Zinc was significantly higher in the exchangeable form as compared to the other forms.  These results suggest that copper is strongly bonded to organic matter as the pH increases and that zinc was readily exchangeable and available to the plants and potentially mobile through the soil profile.  The speciation of Cu and Zn using MINTEQA2, Equilibrium Speciation Model computer program will be presented.