The aim of this project is to assess the bioavailability of phosphorus (P) in municipal wastewater sludge (sewage sludge, SS) depending on the origin (composition) and treatment of waste water. Both biological and chemical precipitation treatments of P will be studied. P availability of waste water sludge will be compared with P availability of the most commonly used organic fertiliser, animal manure, and mineral fertilisers (NPK).
The impact of plant species, soil type, pH and N supply on the bioavailability of P will also be investigated. The range of pH simulates Middle European soils with high pH and Scandinavian soils with low pH. Sludge will be the only P source in the experiments. The contents of iron (Fe), aluminium (Al) and calcium (Ca) depending on the origin and treatment will get special attention, as they are known to bind P into sparingly soluble compounds.
The pot experiments simulate plant P availability during the most critical main growing period of the first growing season. In the incubation experiments, release and fixation of organic and precipitated P will be followed for a longer time period. The field experiments reflect the P availability in the practical field conditions on farms during the two first years.