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The Metal Complexing Capacity and the Nature of the Chelating Ligands of Water Extract of Poultry Litter¹

ABSTRACT

The metal complexing capacity and the nature of the chelating ligands of organic matter extracted from broiler house litter were studied by ion-exchange equilibrium and dissolution methods and infrared spectroscopy.

The water extract of broiler house litter appeared to exhibit a significant chelating effect on the cations Cu²⁺, Zn²⁺, Mg²⁺, and Al³⁺. The amount of organic matter complexed by one mole of metal and the stability of metal complexes increased with increasing pH in the cases of Cu-, Mg-, and Al-complexes, but were unaffected by changes in pH in the case of Zn-complexes. With respect to the divalent ions, the amount of organic matter chelated and the stability of the divalent metal-complexes decreased in the order Cu > Zn > Mg.

Dissolution studies with insoluble Al₂O₃ and Fe₂O₃ powders showed that both Al and Fe were chelated in the aqueous extract, but 10 times more Al than Fe was dissolved in a given time period.

Infrared analysis revealed spectrograms of the ligands similar to those obtained for polysaccharides. However, since the freeze-dried extract contained 9% N, some NH₂ groups must have been present, although bands of these groups were not resolved from overlapping O-H bands. Functional group frequency vibration comparisons at 3,500, 3,200, 1,650, and 1,400 cm^-1 showed that the formation of stable metal-complexes involved carboxyl electrovalent linkages and probably hydroxyl and/or amino coordinate linkages.

¹ Contribution from the Southern Branch, Soil & Water Conservation Research Division, ARS, USDA, in cooperation with the University of Georgia Agr. Exp. Sta. Journal Series Paper no. 760.

² Assistant Professor, University of Georgia Department of Agronomy, Athens, Ga. 30601; Research Soil Scientist, USDA, Watkinsville, Ga. 30677; Head, UGA Dept. of Agronomy, Athens, Ga. 30601; and Research Soil Scientist, USDA, Watkinsville, Ga. 30677, respectively.

Received for publication August 3, 1970. Accepted for publication December 28, 1970.