Assessment of Calcimetry as a Reliable Method for Monitoring Soil Inorganic Carbon Stocks

Abstract

The reliable measurement of the inorganic carbon content of soils and its changes resulting from land management practices and amendments is crucial for precisely quantifying carbon stocks as part of monitoring, reporting, and verification schemes. While various methods are available for evaluating the carbonate content in soils, the most direct approach is calcimetry, which involves the dissolution of solid-phase carbonates and the evolution of gas-phase CO₂ through acid-initiated reactions. Despite being a well-established method, uncertainties about how reliable calcimetry is to measure small changes in soil inorganic carbon (SIC) or how its measurement may be affected by potentially interfering reactions, sample size, and solid–liquid contact call for a dedicated investigation of these effects. The present study demonstrates the reliability of the calcimetry method and its limits through a parametric analysis that investigated the effect of the solid-to-liquid ratio, the presence of unweathered silicate phases, and the presence of copious amounts of organic matter. The results point to the reliable performance of calcimetry within the range of soil conditions that can be expected to be encountered during activities involving enhanced rock weathering and other best management practices that aim to boost the global soil carbon stocks as a climate change mitigation strategy.