Methodological study on pH and electric conductivity measurements in compost samples

Abstract

The present paper describes the influence of compost/solvent relations on pH and electric conductivity (CE) measurements, using water and CaCl2 0.01 M as extractants, in the extract suspension as well as in centrifuged supernatant. According to the results, pHCaCl2 seems to be more independent of extractant quantity, contrarily to aqueous extract measurements, which increases with dilution, described by a quadratic model. As a consequence, measurement must be performed where the curve slope is minimum or null, and where the measurement becomes independent of extractant quantity. For aqueous extract, it happens at relations compost/extractant greater than 1:8, and for CaCl2 extracts, greater than 1:5. pHH2O is higher than pHCaCl2 showing that CaCl2 is a better acidity extractant. EC measurements also show polynomical behavior, therefore must be performed on relations compost/extractant greater than 1:6, where EC values are more independent of extractant quantity. EC could be performed in CaCl2 extract, suspension or supernatant, with respective blank correction.