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.
Bibliographical noteFunding Information:
This research was jointly supported by a research grant no. IS-3963-07 from BARD , The United States-Israel Binational Agricultural Research and development Fund and a research grant from the Israeli Ministry of Agriculture and Rural Development.
- Sewage sludge