Absorption of Ammonia Released from Poultry Manure to Soil and Bark and the Use of Absorbed Ammonia in Solubilizing Phosphate Rock

Composting systems were designed to utilize ammonia (NH₃) released during composting of poultry manure to solubilize phosphate rock (PR). The NH₃ released from decomposing manure was allowed to pass through columns containing soil or bark materials mixed with North Carolina phosphate rock (NCPR) at a rate of 1 mg P g^?1. After eight weeks of incubation, the columns were dismantled and the forms of P and N in PR/soil or PR/bark mixtures were measured. The dissolution of PR was determined from the increases in the amount of soluble and adsorbed P (resin plus NaOH extractable P) or from the decreases in the residual apatite P (HC1 extractable P).

The amounts of NH₄^+-N in the soil and bark columns increased due to absorption of the NH₃ released from poultry manure. No nitrification of absorbed NH₃ occurred, however, unless the soil or bark were reinoculated with a fresh soil solution and incubated for further six weeks.

In the absence of NH₃ absorption, soil and bark materials dissolved approximately 33 percent and 82 percent of NCPR, respectively. The higher dissolution of NCPR in bark was attributed to its higher exchangeable acidity and Ca sink size. There was no increase in NCPR dissolution during the initial NH₃ absorption phase (36 percent and 85 percent dissolution in soil and bark respectively), which may be due to the absence of nitrification. However, during subsequent reincubation when nitrification occurred, the final dissolution of NCPR in the NH₃ treated soil and bark was slightly higher (41 percent and 100 percent, respectively). Protons (H⁺) are released during the oxidation of NH₄⁺ to NO_3? (nitrification) which promote the dissolution of PR. However, most of the H⁺ released during nitrification was involved with soil and bark pH buffering reactions. Only five to 10 percent was involved in PR solubilization in PR/soil mixtures whereas about 50 percent was involved in PR/bark systems.

Bark covers for poultry manure and poultry manure compost heaps have the potential to reduce NH₃ loss and conserve N and may be useful for other purposes such as PR solubilization.