Quantifying Carbon Sequestration from an Enhanced Rock Weathering Application at an Agricultural Field in Nebraska

Authors

Kalley M. Collins, University of Nebraska-LincolnFollow

First Advisor

Trenton E. Franz

Second Advisor

Arindam Malakar

Committee Members

Daniel Snow, Michael Kaiser

Date of this Version

7-2025

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Natural Resource Sciences

Under the supervision of Professors Trenton E. Franz and Arindam Malakar

Lincoln, Nebraska, July 2025

Comments

Copyright 2025, Kalley M. Collins. Used by permission

Abstract

Enhanced Rock Weathering (ERW) is emerging in the voluntary carbon market as a negative emissions technology that sequesters atmospheric carbon dioxide (CO₂) in soils as inorganic bicarbonate. Measurement, Reporting, and Verification (MRV) research focuses on ERW’s impacts on soil health and crop productivity. Accurate modeling of weathering and CO₂ sequestration rates is essential; however, measurements of CO₂ removal (CDR) rates using alkalinity from leachate are not feasible at large scale, thus a soil mass balance cation approach may improve MRV. However, this method has not adequately been tested in field conditions. The proposed project addresses this by improving understanding of how ERW functions in Midwest agricultural soils by studying a cation mass balance approach using magnesium (Mg) and nickel (Ni) as indicators of inorganic carbon sequestration.

This study tested olivine as a soil amendment at an intermediate field scale and found that crop yield was not affected: olivine-treated plots averaged 4.18 Mg/ha, compared to 4.15 Mg/ha in control plots. Olivine application increased average soil pH from 5.55 ± 0.09 to 5.83 ± 0.10; leachate pH increased from 6.37 ± 0.06 to 6.58 ± 0.14 with olivine. CDR rates estimated from lysimeter leachate were 0.015 ± 0.0003 tCO₂e/ha, estimates based on the soil cation mass balance method were 1.11 ± 0.12 tCO₂e/ha. Only 60% of field plots yielded plausible CDR estimates, likely due to soil heterogeneity, repeat sample collection, and measurement uncertainty. These results underscore a key challenge: while leachate-based estimates are likely more direct, they are logistically and economically unscalable, whereas soil-based methods are feasible but prone to background variability.

Electromagnetic Induction (EMI) geophysical mapping was employed to explore spatial variability soil properties, pH, organic matter and cation exchange capacity; no relationship with changes in Mg or Ni concentrations were identified. Soil characteristics may influence weathering processes; EMI alone did not adequately resolve spatial uncertainty observed in soil-based CDR estimates, underscoring the broader challenge of scaling MRV in heterogeneous field conditions. Mass-balance soil approach alone is insufficient for robust MRV at scale. Accurate quantification of ERW-based CDR will require methods that reduce effects of soil heterogeneity and sampling variability.

Advisors: Trenton E. Franz and Arindam Malakar