The impact of alum addition on organic P transformations in poultry litter and litter-amended soil

Poultry litter treatment with alum (Al₂ (SO₄) ₃·18H₂O) lowers litter phosphorus (P) solubility and therefore can lower litter P release to runoff after land application. Lower P solubility in litter is generally attributed to aluminum-phosphate complex formation. However, recent studies suggest that alum additions to poultry litter may influence organic P mineralization. Therefore, alum-treated and untreated litters were incubated for 93 d to assess organic P transformations daring simulated storage. A 62-d soil incubation was also conducted to determine the fete of incorporated litter organic P, which included alum-treated litter, untreated litter, KH₂PO₄ applied at 60 mg P kg ^-1 of soil, and an unamended control. Liquid-state ³¹P nuclear magnetic resonance indicated that phytic acid was the only organic P compound present, accounting for 50 and 45% of the total P in untreated and ahm-treated litters, respectively, before incubation and declined to 9 and 37% after 93 d of storage-simulating incubation. Sequential fractionation of litters showed that alum addition to litter transformed 30% of the organic P from the 1.0 mol L^-1 HCl to the 0.1 mol L^-1 NaOH extractable fraction and that both organic P fractions were more persistent in alum-treated litter compared with untreated litter. The soil incubation revealed that 0.1 mol L^-1 NaOH-extractable organic P was more recalcitrant after mixing than was the-1.0 mol L^-1 HCl-extractable organic E Thus, adding alum to litter inhibits organic P mineralization during storage and promotes the formation of alkaline extractable organic P that sustains lower P solubility in the soil environment.