In the last decade, the 0.01 M CaCl₂ extraction procedure was tested as a multi-nutrient extractant. In 1995-97, international joint research activities were carried out within the COPERNICUS project. Detailed calibration of conventional and the 0.01 M CaCl₂ extraction procedures for pH, Mg and K were published.
The amount of phosphorus extracted using a 0.01 M CaCl₂ solution is very low and reflects the intensity parameter of phosphorus bio-availability. As a readily desorbed P fraction of soils can reflect the soil P-supply and the CaCl₂-P values are in close correlation with P-fertiliser rates and P balance. However, the effects of various soil characteristics on CaCl₂-P values are different and their interpretation is difficult.
Relatively poor correlations were found between amounts of P extracted by conventional and CaCl₂ soil test methods and, therefore, P limit values could not be calculated directly. To characterise the soil P supply at different sites, the CaCl₂ desorbed P and the adsorbed P in a modified Baker Soil Test were also applied.
Soil test results of Hungarian long-term fertiliser experiments and recommended CaCl₂-P limit values, calculated on yield effects and soil characteristics, are discussed.