Abstract/Summary

Poultry production generates large amounts of litter or manure, which can be a valuable source of P for crops. However, litter application rates are usually based on data for mineral P fertilizer recommendations. In order to determine if this is agronomically and environmentally sound, the availability, fractions, and sorptivity of P from poultry litter or KH2PO4 were determined in six Oklahoma soils following incubation for up to 28 d. An average 50% more P from KH2PO4-treated (78 mg kg-1) than from leachate- treated soils (52 mg kg-1) was bioavailable, as determined by extraction with Fe-oxide-impregnated paper strips, after 28-d incubations. Conversely, more NaHCO3-extractable P was found in leachate-treated (66 mg kg-1) than KH2PO4-treated soils (42 mg kg-1). Calculated from Langmuir isotherms, P sorption maxima averaged 548 mg kg-1 for leachate-treated and 304 mg kg-1 for KH2PO4-treated soils, while binding energies averaged 0.527 and 0.456 L mg-1, respectively. The higher P sorption maxima and binding energies of leachate-treated soils may result from the formation of Ca-P complexes, given the increased Ca content of these soils. The different reaction in soil of P added as poultry litter leachate to that added as KH2PO4, indicates manure application rates should be based on soil texts that are sensitive to P source-dependent sorption characteristics and/or manure trials, and not just on mineral fertilizer trials.