Effects of anaerobically digested poultry manure on soil phosphorus adsorption and extractability

Research in the past has indicated that large additions of animal manures to soil can reduce soil P adsorption and increase P extractability. However, application rates used in many studies are unrealistic with respect to crop fertilization and land disposal due to the excessive quantities of N applied with the manures. The objective of this study was to evaluate effluent from a poultry manure anaerobic digester applied to a Hayesville loam soil (clayey, oxic, mesic, Typic Hapludult) on soil P adsorption and extractability after three incubation periods (0, 30, and 90 d). Effluent solids were applied at rates corresponding to 753 through 7530 mg N kg^-1 soil. Langmuir equation parameters (from least square fitted data; R² > 0.98) were used as a basis to compare the influence of treatments on P adsorption properties of the soil. The P adsorption maxima parameter was not influenced by any of the effluent treatments. The parameter related to P bonding energy of the soil was reduced 33 and 41%, respectively, by mid and high rate effluent applications. A similar reduction was not observed for the low rate treatment, which corresponded to fertilizer application of 100 mg N kg^-1 soil. Extractable soil P increased in a predictable manner with increased effluent solids application for all three incubation periods. These increases in extractable P could be described by linear regression equations. The slopes of these lines indicate that a 1-g addition of effluent solids to 1-kg soil-accounts for increases in extractable P of 3 to 6 mg kg^-1.