Perspektywy wprowadzenia w Polsce metody pomiaru pH w 0,01 mol/dm3 CaCl2

The investigations on possibility of soil testing in universal extract 0,01 mol/dm³ CaCl₂ have been conducted in 1995 - 1997 in Poland, Czech Republic. The Netherlands and Hungary in a frame of international project Copernicus. One of a basic parameter of soil fertility, which can be determined in calcium chloride extract is hydrogen cation concentration expressed as pH value. The purpose of investigations was to compare pH value determined in 0,01 mol/dm³ CaCl₂ and in 1 mol/dm³ KCl extract, used as a standard method in agrochemical investigations in most countries, as well as determination of critical values (the method calibration) of soil acidity ranges for „universal” method. In Poland about 1300 soil samples were analyzed by both methods. The pH values obtained in both compared extracts were highly correlated. Nevertheless pH values in 0,01 mol/dm³ CaCl₂ were significantly higher then in 1 mol/dm³ KCl in samples from very acidic, acidic and slightly acidic soils. In alkaline soils pH values by „universal” method are lower then by „standard” one. In neutral soils the results of both methods are equal. For the practical purposes the quadratic regression equation can be used for comparison of pH values determined by the both methods: pHCaCl₂ = 1.339 pHKCl- 0.051 pHKCl^2. As the practical purposes we understand calibration of the method with CaCl₂ and determination of optimal doses of lime on the basis of existing calibration for the method with potassium chloride.