Steady‐State Procedure for Determining the Effective Particle‐Size Distribution of Soil Carbonates

A pH‐stat procedure in conjunction with the equal‐diameter reduction model was used to estimate the effective particle‐size distribution of soil carbonates. Samples were titrated by pH‐stat at pH 3 and 5. The cumulative dissolution data and rate constants for the dissolution of Iceland‐spar calcite were incorporated into simultaneous equations to obtain estimates of the effective particle‐size distributions of soil carbonates. Results obtained by this method from 23 calcareous soils were compared with results obtained by a sieving and sedimentation procedure. The pH‐stat procedure resulted in the estimation of a higher proportion of clay‐size carbonates than was obtained by the sieving and sedimentation procedure. This difference was attributed predominantly to the higher reactivity of soil carbonates compared with Iceland‐spar calcite. The pH‐stat procedure was especially useful for obtaining quantitative estimates of the proportion of highly reactive clay‐size carbonate with <0.2‐µm effective particle diameters.