Reaction in Soil of Phosphorus Released from Poultry Litter

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 KH 2 PO 4 were determined in six Oklahoma soils following incubation for up to 28 d. An average 50% more P from KH 2 PO 4 ‐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 NaHCO 3 ‐extractable P was found in leachate‐treated (66 mg kg −1 ) than KH 2 PO 4 ‐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 KH 2 PO 4 ‐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 KH 2 PO 4 , indicates manure application rates should be based on soil tests that are sensitive to P source‐dependent sorption characteristics and/or manure trials, and not just on mineral fertilizer trials.