Phosphorus fractionation in chicken and duck litter burned at different temperatures

Disposal of poultry litter (PL) is one of the major concerns of poultry farmers. Burning of PL is an economically viable and environmentally safe method for poultry waste management. Phosphorus (P) fractionation in waste material is important for predicting its bioavailability. The objective of this study was to evaluate the effects of different temperatures on the release of P fractions in the chicken litter ash (CLA) and duck litter ash (DLA). The material was ashed at five temperatures: 200, 400, 600, 800, and 900 degrees C. Phosphorus was fractionated into readily plant-available P, labile inorganic P (another plant-available fraction), sesquioxide-associated P, and Ca-associated P by sequentially extracting with deionized water, 0.5 M of NaHCO3, 0.1 M of NaOH, and 1 M of HCl, respectively. Total P was determined by acid digestion. The inorganic P was also determined using Peterman citric acid and citric acid extractions. Loss-on-ignition, electrical conductivity (EC), and pH were measured. The experiment showed that weight loss was highly varied under different temperatures. As expected, increasing temperature increased weight loss. Except water-soluble P, all P fractions in samples increased with the increasing temperature. For both manures, P release decreased in the order: Ca-associated P > labile inorganic P > sesquioxide-associated P > readily plant-available P. Regardless of the burning conditions, sesquioxide- and Ca-associated P were higher in DLA than CLA, whereas the labile inorganic P (NaHCO3-P) was higher in CLA. For CLA, the sum of inorganic P that was found at its peak at 600 degrees C was 4.2-fold higher than unburned CL, whereas for DLA, the sum of inorganic P was 4.7-fold higher than unburned DL. Total P was higher in CLA than DLA with its highest amount at 900 degrees C. Peterman citric acid and citric acid-extractable P was substantially higher in CLA samples. Citric acid P was found more than Peterman citric acid P, and highest values were recorded at 600 degrees C. Irrespective of temperature, water-soluble P significantly decreased with burning. The burning practice seemed to affect the exchangeable cations. Magnesium was highest, whereas Ca2+ was lowest at 600 degrees C. The K+ was enhanced by temperature. The Ca2+ and Mg2+ contents were higher in DLA as compared with CLA. Potassium was highest in CLA. The CLA exhibited higher EC and lower pH values than DLA. Both EC and pH increased with temperature. The low water-soluble P in ash could suggest that the use of burned PL would be less of a water pollution problem in the fields.