Carbon dioxide removal through enhanced weathering of basalt in acidic soils under sugarcane

Summary

Weathering of silicate rocks regulates atmospheric CO2 over geological timescales. Enhanced weathering (EW) accelerates this process through the crushing and spreading of rocks such as basalt over large areas of land or the sea. EW of basalt requires carbonic acid weathering to convert atmospheric CO2 into bicarbonate, allowing transportation into the rivers and the sea, where it can precipitate as calcium carbonate.

Application of basalt has the co-benefit of a liming effect and addition of some nutrients. Holden et al. (2024) found negligible leached CDR from EW of basalt in acidic soils. This research found that acids stronger than carbonic acid weathered the basalt and prevented bicarbonate generation. Acidic soil pH increases rates of weathering, however for reasons mentioned above, limits in-field CDR, and acidic soils are widespread, including in the high rainfall tropics. Under sugarcane, potential sources of strong acids include the oxidisation of ammonium from nitrogen fertilisers, and the mineralisation of organic matter and plant root exudation. For EW to be feasible as a technology for CDR, further experimentation is required to understand the influence of soil pH and acidifying processes.

Objectives

1. Determine the mechanisms controlling carbon dioxide removal following application of crushed basalt and agricultural lime (individually and combined) to acidic soil under sugarcane in the wet tropics.
2. Determine the effects of basalt and lime application (individually and combined) on crop production and soil fertility on acidic soil under sugarcane in the wet tropics.
3. Determine the effects of basalt and lime on crop production, soil fertility and carbon dioxide removal in nonacidic soils in the dry tropics under different cropping systems, including sugarcane.

Expected Outputs

1. Knowledge of the effects of enhanced weathering on carbon dioxide capture, crop production and soil fertility under sugarcane and other crops in the tropics
2. Knowledge of the key climate, soil and management factors determining carbon dioxide capture, crop production and soil fertility resulting from enhanced weathering in the tropics.
3. Summary of potential benefits and costs of enhanced weathering in tropical agriculture.

Expected Outcomes

Potential outcomes and impact are:
1. A new source of income for sugarcane growers from carbon credits for CO2 removal via enhanced weathering. The knowledge gained will enable optimised deployment and guidance for monitoring, reporting and verification.
2. Reduced greenhouse gas emissions from sugarcane cultivation. This will be achieved by a) substituting basalt for lime to ameliorate soil acidity in appropriate situations, thus avoiding the CO2 emission from lime application, and b) reduced N2O emission from the raised soil pH.
2. Long-term cost-effective maintenance of soil health and crop productivity, through slow and sustained provision of nutrients from weathering basalt (P, Si, Ca, Mg, K), liming effect and formation of clays.

SRA PROJECT CONTACT: Cathy Mylrea

RESEARCH AGENCY: James Cook University

CHIEF INVESTIGATOR: Fredrick Holden

PROJECT NUMBER: 2024/102

END DATE: 9/4/2028