Dynamics of phosphorus phytoavailability in soil amended with stabilized sewage sludge materials

Reducing the environmental risk of soluble P loss from sludge-amended soils is essential for increasing soils capacity to utilize sewage sludge beneficially. Fresh dewatered anaerobically digested sewage sludge (FSS), stabilized with ferrous sulphate (FeSul-SS), calcium oxide (CaO-SS) and aluminum sulphate (alum-SS), each at three chemical-to-FSS ratios, or by composting (BSC), was applied to alluvial soil at rates of 150 and 300mg P kg ^-1 soil. Changes in P phytoavailability in comparison to KH ₂PO ₄-amended soil were probed during 100days of incubation by a P-bioassay and were compared to the concentration of water-soluble P (WSP) and Olsen-P. P phytoavailability was notably linked to the incubation duration and the stabilization process. In general, P phytoavailability at equal P-addition rates was KH ₂PO ₄ >>alum-SS>BSC≥FSS>CaO-SS >>FeSul-SS; and it was positively related to the added P rates, although with quite different patterns among the various sludge products. The concentration of inorganic WSP (WSP _i) extracted from the soil increased following the application of FSS or BSC, and additional P mineralization further increased its concentration during incubation. In contrast, in most cases the chemically stabilized sludges, especially the FeSul-SS, showed considerably reduced inorganic WSP concentrations relative to the untreated soil. The total WSP, Olsen-P and organic WSP (WSP _o) positively correlated to P phytoavailability, indicating that WSP _o plays a role in plant P utilization in these soils. It is concluded that all the chemically stabilized sewage sludge studied effectively controlled WSP _i in soil while still supplying P to support plant growth.