Phosphorus Mineralization and Availability in Soil Amended with Biosolids and Animal Manures

Abstract

ABSTRACT Land spreading of biosolids (sewage sludge) and animal manures on agricultural soils is a means of disposal that is both environmentally and economically attractive. As with any soil amendment, there is potential for adverse impact from the land application of these materials. Applying biosolid or manure to meet crop N requirements can often result in excessive P application. A greenhouse bioassay study was conducted to evaluate bioavailable P from biosolid and manure amendments and to determine the effectiveness of the modified Morgan soil test (pH 4.8, 1.25 M ammonium acetate) and an in situ anion exchange membrane resin P soil test (PInSitu) to estimate plant-available P in the amended soil. The effects of biosolid stabilization processes on P availability were investigated by using lime stabilized (LSB), composted (CB), anaerobically digested (ADB) and unstabilized (UB) biosolids. The three animal manures studied were: dairy (DM), poultry (PM), and swine (SM). Triple super phosphate (TSP) served as an inorganic reference. Cumulative net P uptake by ryegrass (Lolium perenne L.) was highest for DM and SM, intermediate for PM, LSB, UB and TSP, and lowest for CB and ADB. Soil test P levels measured by the Morgan and PAEM methods were highly correlated (r = 0.88, p = 0.01). The P uptake by ryegrass (Lolium perenne L.) agreed well with predicted P availability, indicating that both the modified Morgan soil test and in situ exchange resin methods are appropriate for determining P availability in biosolid- and manure-amended agricultural soils.