P Solubility of Inorganic and Organic P Sources

P solubility of mineral and organic fertilizers can be estimated by a variety of different chemical extraction methods. In Europe, the characterization of P solubility in fertilizers is regulated in the European fertilizer regulation 2003/2003 for commercial fertilizers, assigning different methods to the various fertilizer types. Relationships between chemical solubility and agricultural performance/P availability for plants have been documented in numerous pot and field trials. Non-commercial fertilizers like farmyard manures and slurries, on the other hand, as well as “new products” based on recycling materials such as sewage sludge ash, are not included in this regulation yet, and a number of methods, designed for mineral fertilizers as well as for P solubility in soils, have been tested over the last couple of years to adequately characterize these products. This review gives a critical overview of the chemical extraction methods currently practiced and/or tested in the European countries, and their performance as estimates for plant availability of fertilizer P from inorganic and organic P sources.