The measurement of the cation-exchange capacity of composts for the estimation of the degree of maturity

Abstract

In order to estimate the degree of maturity of composts, the method for the measurement of CEC of some composts was developed. The method is similar in principle to those developed for the measurement of CEC of plant roots. A 200 mg of milled compost sample is washed with HCI to replace the exchangeable cations. After the excess HCI is removed by washing with distilled water, Ba(OAc)₂ solution (pH 7.0) is added to the sample, and the mixture is stood overnight. After filtration, the sample is leached with another Ba(OAc)₂ solution, and then the released proton is titrated with standard NaOH solution using a potentiometer. The amount of released proton gives the CEC. The method gives reproducible and accurate values, but requires a particular apparatus. It takes a relatively long time to carry out the whole procedure. A simplified method, in which the sample is stood for only 1 hr for the equilibration with Ba(OAc)₂ solution and the titration is carried out using thymol blue as indicator, was also recommended.