BIOAVAILABILITY OF COPPER, MANGANESE, AND ZINC IN POULTRY LITTER

Poultry litter is a useful agricultural by-product but its potential f or environmental pollution requires clarification. A poultry litter fr om north Georgia containing 1196, 944, and 631 mg/kg Cu, Mn, and Zn re spectively 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 p ure quartz sand and Cecil (clayey, kaolinitic, thermic Typic Kanhaplud ult) and Lakeland (thermic, coated Typic Quartzipsamment) soils at soi l pH regimes of approximate to-5 and 7. Sudax [Sorghum bicolor (L.) Mo ench)] 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 c oncentrations 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 t he more clayey Cecil soil where reducing conditions in the pots may ha ve been responsible for excessive solubilization of Mn. Soil pH was im portant in determining both ammonium bicarbonate-DTPA and 0.1 M NaNO3 extractable soil Cu, Mn, and Zn. Significant (P < 0.01) correlations w ere found between soil Cu, Mn, and Zn extracted by these extractants a nd 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 rec eived 6 Mg/ha of poultry litter per annum for 16 yr.