Evaluation of Two Methods to Measure Soluble Phosphorus In Broiler Litter.

Water-soluble phosphorus (P) in broiler litter is usually extracted by shaking broiler litter with deionized water in a 1:200 ratio.  Because a typical pH for litter is 8.0, extraction with deionized water occurs at an alkaline pH, which is likely to limit the solubility of phosphorus compounds.  Research in Georgia (USA) has shown that litter pH equilibrates to the soil pH within a few weeks after surface application.  Typical pH values in Georgia soils range between 5 and 6.  Consequently, once litter equilibrates to a lower pH, the solubility of P compounds in the litter would increase, releasing more soluble P to the soil. This study was conducted to determine the amount of  inorganic P extracted from broiler litter with deionized water (unbuffered) or MES buffer (pH 6) and compare it to the amount of water-soluble, inorganic P released from litter mixed with soil (pH 6) during a 42-d incubation.  The amount of inorganic P extracted with deionized water (3,358 mg P kg^-1) was within the range of inorganic P released from litter by 1 to 3 days after application (2,900 to 4,100 mg P kg^-1), but was lower than the amount of inorganic P released by 42 days (5,700 mg P kg^-1).  In contrast, the amount of P extracted with MES buffer (5,800 mg P kg^-1) was similar to the amount of inorganic P released by 42 days after application.  These results suggest that extraction of broiler litter with MES buffer at pH 6 may be useful to estimate inorganic P released as broiler litter pH equilibrates with soil pH.