Direct evidence for enhanced mineral weathering in cropland verified by quantitative X-ray powder diffraction

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S0883292726001939

Authors: Kohei Kurokawa, Atsushi Nakao, Kazuki Azuma, Hodaka Tomita, Katashi Kubo, Kazuki Nomura, Junta Yanai

12 May 2026

https://doi.org/10.1016/j.apgeochem.2026.106869

Highlights

•Direct evidence for basaltic mineral weathering in soils via enhanced rock weathering is lacking.

•Plagioclase and pyroxene, as basaltic minerals, were quantified by X-ray powder diffraction (XRPD).

•XRPD detected significant decreases of these minerals in rootzone soils after buckwheat cultivation.

•XRPD enables quantitative verification of mineral weathering under field conditions.

Abstract

Enhanced rock weathering (ERW) is a promising carbon dioxide (CO2) removal (CDR) strategy that involves applying powdered rocks such as basalt to croplands to accelerate the natural weathering of rock minerals. However, despite numerous recent field investigations, direct evidence for the weathering of rock minerals in soils is lacking because most studies rely on cation budgets to estimate ERW-induced CDR. In this study, buckwheat was cultivated for 2.5 months in plots with and without basalt powder applied at a rate of 150 t ha−1, and the decrease in basaltic mineral contents of the soils during the cultivation period was measured using quantitative X-ray powder diffraction (XRPD). Applying basalt powder significantly increased the contents of basaltic minerals such as plagioclase (e.g., labradorite and bytownite) and pyroxene in the soils, and the basaltic mineral contents subsequently decreased significantly in the rootzone after cultivation. The decrease was about 8.5 times greater in the rootzone than outside the rootzone. The percentage decrease relative to the input in the rootzone was 25.6% for labradorite, 58.8% for bytownite, and 65.1% for pyroxene, reflecting the theoretical dissolution mass and the more rapid weathering of bytownite and pyroxene compared to labradorite. The maximum CDR associated with the weathering of these minerals was estimated as 7.2 t CO2 ha−1 over 2.5 months. These results provide the first quantitative evidence for the weathering of basaltic minerals applied to cropland and demonstrate the feasibility of applying state-of-the-art XRPD analysis to the monitoring, reporting, and verification of ERW-induced CDR under field conditions.

Source: ScienceDirect