Phosphorus in Poultry Litter and Soil: Enzymatic and Nuclear Magnetic Resonance Characterization

Abstract

Knowledge of the P forms in poultry litter (PL) and their transformations in soil will help improve our understanding of the long‐term role of P in eutrophication. In this study, samples of PL and pasture soils with and without 20 yr of PL application were sequentially extracted to separate P into H2O, 0.5 mol L−1 NaHCO3, 0.1 mol L−1 NaOH, and 1 mol L−1 HCl fractions. After appropriate dilution and pH adjustment, the fractions were incubated in the presence of orthophosphate‐releasing enzymes. Cross‐examination of the solution 31P nuclear magnetic resonance spectra of the enzymatically treated and untreated fractions revealed that the peaks of organic P (Po) species of the enzymatically treated fractions became very weak or disappeared, confirming enzymatic hydrolysis of Po in the untreated fractions. Although the majority of P in the NaOH and HCl fractions of PL was in organic forms, these stable Po forms could be subjected to enzymatic hydrolysis after being applied to soil, an occurrence that was supported by the soil P data. Compared with soil without litter applied, 20 yr of PL application increased the pools of both labile and stable inorganic P in the soil; however, repeated application of PL did not lead to a significant accumulation of hydrolyzable Po in NaOH and HCl fractions, indicating that the stable Po must have been converted to other forms. The transformation of stable PL Po observed in this study could be an important mechanism for maintaining a balance between labile and immobile P in soils.