MEASUREMENT OF PH IN SOIL SAMPLES FROM A CUTOVER PEATLAND IN SWEDEN - THE EFFECT OF ELECTROLYTE AND SOLUTION SOIL RATIO

Ninety-seven organic soil samples were collected from a cutover peatland in west-central Sweden and soil pH (12.5:1 v/w solution:soil) was measured in water (pHW), 0.01M CaC12 (pHCa) and 1M KCl (pHK). The pH values obtained by these three methods were found to be highly correlated over the pHW range 3.95 to 5.91. Base saturation and pHK were shown to influence the difference pHW-pHK, while electrical conductivity and CEC also influenced the difference pHW-pHCa. Increasing the solution:soil ratio from 5 to 80 (v/w) or 1 to 10 (v/v) increased pHW significantly, while there was no significant effect on pHK and pHCa. The difference between pHW values at different solution:soil ratios increased with increasing pH, C content, titratable acidity (pH 7.0) and base saturation and decreased with increasing CEC. It was shown that on organic soil samples the water:soil ratio should be less or equal to 10 for v/w ratios or less or equal to 2 for v/v ratios to attain stable and reliable pHW values.