Holden, Fredrick J., Davies, Kalu, Bird, Michael I., Hume, Ruby, Green, Hannah, Beerling, David J., and Nelson, Paul N. (2024) In-field carbon dioxide removal via weathering of crushed basalt applied to acidic tropical agricultural soil. Science of the Total Environment, 955. 176568.

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Abstract

Enhanced weathering (EW) of silicate rocks such as basalt provides a potential carbon dioxide removal (CDR) technology for combatting climate change. Modelling and mesocosm studies suggest significant CDR via EW but there are few field studies. This study aimed to directly measure in-field CDR via EW of basalt applied to sugarcane on acidic (pH 5.8, 0–0.25 m) Ultisol in tropical northeastern Australia, where weathering potential is high. Coarsely crushed basalt produced as a byproduct of gravel manufacture (<5 mm) was applied annually from 2018 to 2022 at 0 or 50 t ha−1 a−1, incorporated into the soil in 2018 but not in subsequent years. Measurements in 2022 show increased soil pH and extractable Mg and Si at 0–0.25 m depth, indicating significant weathering of the basalt, but showed no increase in crop yield. Soil inorganic carbon content and bicarbonate (HCO3−) flux to deep drainage (1.25 m depth) were measured to quantify CDR in the 2022–2023 wet season (i.e. one year). Soil inorganic carbon was below detection limits. Mean HCO3− flux was 3.15 kmol ha−1 a−1 (±0.40) in the basalt-treated plots and 2.56 kmol ha−1 a−1 (±0.18) in the untreated plots but the difference (0.59 kmol ha−1 a−1 or 0.026 t CO2 ha−1 a−1) was not significant (p = 0.082). Most weathering of the basalt was attributed to acids stronger than carbonic acid. These were, in decreasing order of contribution, surface-bound protons (inherent soil acidity), nitric acid (from nitrification), organic acids, and acids associated with cation uptake by plants. These results indicate in-field CDR via EW of basalt is low where soil and regolith pH is well below the pKa1 of 6.4 for H2CO3. However, increased soil pH, and the consumption of strong acids by weathering will eventually lead to reduced CO2 emission from soil or evasion from rivers, with continued basalt addition.

Item ID:	84066
Item Type:	Article (Research - C1)
ISSN:	1879-1026
Keywords:	Australia,Carbon capture,Climate change,Enhanced weathering,Negative emission technology,Sugarcane
Copyright Information:	© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Date Deposited:	19 Nov 2024 22:06
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