Enhanced rock weathering progress in North Queensland

What if you could reduce the amount of CO2 entering the atmosphere simply by scattering crusher dust in a crop?

Australian scientists are studying the possibility of mitigating climate change by speeding up the climatic effect of weathering.

It’s a process known as enhanced rock weathering (ERW), and it has been the subject of recent research around the world.

Researchers led by James Cook University’s Associate Professor Paul Nelson have been conducting one of the world’s first field trials in Gordonvale, Far North Queensland, for the past five years as part of the University of Sheffield-based Leverhulme Centre for Climate Change Mitigation.

“This technique needs a few years to study properly,” Nelson says.

“What I am happy to say at this point is that the weathering is measurable, and is proceeding at quite a reasonable rate.”

Cosmos reported 18 months ago progress on British research into this process: ”This process makes soil more alkaline – and thus, more likely to react with carbon dioxide in the air, turning it into carbonates and keeping it out of the atmosphere. The method can also reduce the amount of nitrous oxide (another greenhouse gas), and reverse soil acidification. This has the added advantage of lowering farmers’ reliance on fertilisers.”

Since 2018, the JCU team has been spreading basalt pieces of less than 4mm across sugar cane fields in Gordonvale, using crusher dust because it is affordable and readily available.

Nelson says enhanced weathering is a process that accelerates natural weathering by spreading the fine rock over the surface of the land to speed up the chemical reaction between the rocks, the water and the air.

When the rocks are exposed to water and air, they dissolve to clay and other materials and form carbonic acid. The chemical composition of the minerals is changed and the process removes CO2 from the air.

An American Geophysical Union (AGU) paper published this year found enhanced weathering on croplands was a “promising negative emissions concept”.

“Our study provides strong support for the assertion that ERW represents a resilient carbon capture strategy that is non-competitive for arable land and can foster CO2 removal at the gigaton scale.”

Continued research, Nelson says, is critical given start-up companies are already dealing in carbon credits relating to enhanced weathering before anyone really knows how much carbon dioxide is actually being removed by ERW.

Nelson hopes the Gordonvale field trials will help. The study will also go further to model the effectiveness of using the technique across Australia – another first.

“While this technique is not for everywhere, there are significant areas throughout eastern Australia where there is an adequate supply of basalt,” Nelson says. “Western Australia, for example, doesn’t have as much basalt.”

He says basalt, a volcanic rock that forms the basis of much of the agriculturally productive soils across Australia, is being used for the field trials partly because it does not include potentially harmful minerals.

Lime is also being applied in the sugar cane crops to raise the pH of the soil to accelerate the process.

Studies have also shown enhanced rock weathering can improve the yield of crops, but Nelson says this benefit appears to be limited if the crop is already well managed.

The next four years of the Gordonvale study will continue to look at analysis of leachate for pH, alkalinity, nitrate, ammonium and other ions, and soil and plant tissue after harvest to measure evidence of carbon dioxide removal.

The AGU paper states simulations show that with a fixed rate of 10 tons of basalt dust per hectare on all global croplands, the technique could sequester more than 200 gigatons of carbon dioxide over a 75-year period.