BIOAVAILABILITY OF COPPER, MANGANESE, AND ZINC IN POULTRY LITTER

Poultry litter is a useful agricultural by-product but its potential for environmental pollution requires clarification. A poultry litter from north Georgia containing 1196, 944, and 631 mg/kg Cu, Mn, and Zn respectively was used to study the bioavailability of these metals in a short term greenhouse pot experiment. Metal uptake from poultry litter applications equivalent to 0, 15, 30, and 60 Mg/ha were compared on pure quartz sand and Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) and Lakeland (thermic, coated Typic Quartzipsamment) soils at soil pH regimes of approximate to-5 and 7. Sudax [Sorghum bicolor (L.) Moench)] was used as test crop for metal uptake from 1 kg of soil during a 21-d growth period. For the litter treatments, the Cu, Mn, and Zn concentrations were in the ranges 5 to 15, 62 to 1933, and 19 to 55 mg/kg. The Cu and Zn plant concentrations were in the normal range, while toxic Mn concentrations (>400 mg/kg) were found only in the case of the more clayey Cecil soil where reducing conditions in the pots may have been responsible for excessive solubilization of Mn. Soil pH was important in determining both ammonium bicarbonate-DTPA and 0.1 M NaNO3 extractable soil Cu, Mn, and Zn. Significant (P < 0.01) correlations were found between soil Cu, Mn, and Zn extracted by these extractants and plant uptake, while inclusion of soil pH improved the significance of the, regressions. Analyses of field soils revealed the build-up of possible toxic levels of Cu, Mn, and Zn in only one soil which had received 6 Mg/ha of poultry litter per annum for 16 yr.