Determination of compost pH

The objective of the work described in this paper was to establish a means of pH measurement for immature and mature compost, using standard laborator y equipment, that is rapid, accurate and precise. A series of experiments w ere carried out to investigate the influence on pH measurements of the size of compost sample used, diluent types, the time between sample collection and measurement, the standing time after dilution, and the dilution ratio. Linear relationships between dilution ratios within a certain range and pH values obtained under each dilution were established and the pH value of th e original compost was inferred by extrapolating the linear equation to zer o dilution. A practical method is proposed to determine pH on the basis of measurements at two dilution ratios for each sample, and using these measur ements to establish the zero-dilution pH for the sample. The measured pH is calculated from the means of a number of such determinations. The number o f samples required for determining pH to a specific accuracy is discussed.