Rock could aid humanity

Farming crops with crushed rocks could help to improve global food security and reduce the amount of CO₂ entering the atmosphere, a new study has found.

They key is to make sure you’re adding fast-reacting silicate rocks to croplands. These could capture CO₂ and give increased protection from pests and diseases while restoring soil structure and fertility.

Professor David Beerling, lead author of the research, said: “Human societies have long known that volcanic plains are fertile, ideal places for growing crops without adverse human health effects, but until now there has been little consideration for how adding further rocks to soils might capture carbon.

“This study has transformed how we think about managing our croplands for climate, food and soil security. It helps move the debate forward for an under-researched strategy of CO₂ removal from the atmosphere – enhanced rock weathering – and highlights supplementary benefits for food and soils.

“The magnitude of future climate change could be moderated by immediately reducing the amount of CO₂ entering the atmosphere as a result of energy generation. Adopting strategies like this new research that actively remove CO₂ from it can have a massive impact and be adapted very quickly.”

The research, published in Nature Plants, examined the approach which involves amending soils with abundant crushed silicate rocks, like basalt, left over from ancient volcanic eruptions. As these minute rock grains dissolve chemically in soils, they take up carbon dioxide and release plant-essential nutrients.

Critically, enhanced rock weathering works together with existing managed croplands. Unlike other carbon removal strategies being considered, it doesn’t compete for land used to grow food or increase the demand for freshwater. Other benefits include reducing the usage of agricultural fertilizers and pesticides, lowering the cost of food production, increasing the profitability of farms and reducing the barriers to uptake by the agricultural sector.

Crushed silicate rocks could be applied to any soils, but arable land is the most obvious since it is worked and planted annually. It covers some 14 million square kilometres or 10 per cent of the global land area.

Arable farms already apply crushed rock in the form of limestone to reverse acidification of soils caused by farming practices, including the use of fertilizers. Managed crops, therefore, have the logistical infrastructure such as the road networks and machinery needed to undertake this approach at scale. These considerations could make it straight forward to adopt.

Professor Stephen Long at the University of Illinois Champaign-Urbana, and co-author of the study added: “Our proposal is that changing the type of rock, and increasing the application rate, would do the same job as applying crushed limestone but help capture CO₂ from the atmosphere, storing it in soils and eventually the oceans.

“Global warming is a problem that affects everyone on the planet. Scientists generally have done a poor job of getting across the point that the world must reduce emissions of greenhouse gases from fossil fuels and combine this with strategies for extracting carbon dioxide from the atmosphere to avoid a climate catastrophe.”

One of the features of the paper I like is that the authors acknowledge it’s not enough that the idea works. There’s also got to be public trust, and that cannot be taken for granted. Any news that you’re changing what gets added to farmland has got to be a concern for people living downstream of the farms. There’s already enough of a problem with agricultural run-off flowing downstream.

Figure 1 in the paper shows there are advantages to the run-off from the treated fields. Assuming there are no other changes in agricultural practice, there still will be material lost into run-off, the this should have a higher Silicon to Nitrogen ratio. Silicon is simply not as useful a nutrient as Nitrogen, so the effect of Nitrogen, in whatever form it enters the river system, will be diluted. In the seas, the authors believe increased alkalinity could offset some of the acidification of oceans. Given the impacts of dead zones at the mouths of major rivers, that’s a reasonable goal. A healthier ocean should produce more marine snow https://botany.one/2017/02/toxin-tainted-submarine-snow/ which might help lock away more carbon.

It also seems a practical solution to the problem, if suitable sources of rock can be found. Farmers already apply material to their fields, so this doesn’t require radical new processes. It might also complement some other projects. For example, if organogenic dolomite could be created by an industrial process, using microbes to create the rock, then there could be benefits to applying this to soil, building in carbon sequestration into the creation of the minerals, their use and their disposal.

That might be a bit of a leap at the moment. Dolomite synthesis isn’t a commercial tool yet, but there are other projects that could integrate with Beerling et al.’s field treatments. Adding sequestration to reducing emmisions would be a helpful tool tackling the carbon problem, and getting the CO₂ out of the atmosphere is a topic on a lot of minds.

Professor James Hansen from the Earth Institute at Columbia University and co-author of the work, added: “Strategies for taking CO₂ out of the atmosphere are now on the research agenda and we need realistic assessment of these strategies, what they might be able to deliver, and what the challenges are.”