Soil Calcimetry Dynamics to Resolve Weathering Flux in Wollastonite-Amended Croplands

Francisco S. M. Araujo and Rafael M. Santos ()
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Francisco S. M. Araujo: Department of Civil, Environmental, and Water Resources Engineering, College of Engineering, University of Guelph, Guelph, ON N1G 2W1, Canada
Rafael M. Santos: Department of Civil, Environmental, and Water Resources Engineering, College of Engineering, University of Guelph, Guelph, ON N1G 2W1, Canada

Land, 2025, vol. 14, issue 10, 1-24

Abstract: Enhanced Rock Weathering (ERW) is a promising carbon dioxide removal (CDR) strategy that accelerates mineral dissolution, sequestering atmospheric CO 2 while improving soil health. This study builds on prior applications of soil calcimetry by investigating its ability to resolve short-term carbonate fluxes and rainfall-modulated weathering dynamics in wollastonite-amended croplands. Conducted over a single growing season (May–October 2024) in temperate row-crop fields near Port Colborne, Ontario—characterized by fibric mesisol soils (Histosols, FAO-WRB)—this study tests whether calcimetry can distinguish between dissolution and precipitation phases and serve as a proxy for weathering flux within the upper soil horizon, under the assumption that rapid pedogenic carbonate cycling dominates alkalinity retention in this soil–mineral system. Monthly measurements of soil pH (Milli-Q and CaCl 2 ) and calcium carbonate equivalent (CCE) were conducted across 10 plots, totaling 180 composite samples. Results show significant alkalinization ( p < 0.001), with average pH increases of ~+1.0 unit in both Milli-Q and CaCl 2 extracts over the timeline. In contrast, CCE values showed high spatiotemporal variability (−2.5 to +6.4%) without consistent seasonal trends. The calcimetry-derived weathering proxy, log (Σ ΔCCE/Δt), correlated positively with pH (r = 0.652), capturing net carbonate accumulation, while the kinetic dissolution rate model correlated strongly and negatively with pH (r ≈ −1), reflecting acid-promoted dissolution. This divergence confirms that the two metrics capture complementary stages of the weathering–precipitation continuum. Rainfall strongly modulated short-term carbonate formation, with cumulative precipitation over the previous 7–10 days enhancing formation rates up to a saturation point (~30 mm), beyond which additional rainfall yielded diminishing returns. In contrast, dissolution fluxes remained largely independent of rainfall. These results highlight calcimetry as a direct, scalable, and dynamic tool not only for monitoring solid-phase carbonate formation, but also for inferring carbonate migration and dissolution dynamics. In systems dominated by rapid pedogenic carbonate cycling, this approach captures the majority of alkalinity fluxes, offering a conservative yet comprehensive proxy for CO 2 sequestration.

Keywords: soil inorganic carbon (SIC) dynamics; pedogenic carbonate formation; silicate mineral weathering; carbon sequestration; soil pH evolution; rainfall–soil carbon interactions; field-based soil monitoring; land-based climate regulation (search for similar items in EconPapers)
JEL-codes: Q15 Q2 Q24 Q28 Q5 R14 R52 (search for similar items in EconPapers)
Date: 2025
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