Agricultural liming in the US is a large CO2 sink, say researchers

(Press-News.org) Adding lime to agricultural soils can remove CO2 from the atmosphere, rather than cause CO2 emissions, claims new research.

The findings, based on over 100 years of data from the Mississippi River basin and detailed computer modelling, run counter to international guidelines on reducing agricultural emissions.

The research is presented today [Thursday 10 July] at the Goldschmidt Conference in Prague.

The team, from the Yale Centre for Natural Carbon Capture at Yale University, show that the addition of acidity, in the form of atmospheric pollution and fertilisers, is the main driver for CO2 emissions from soils. By calculating emissions based on acid inputs, they show how emissions may be being underestimated in some cases and the potential for lime to reduce emissions is being overlooked.

Agriculture is one of the largest greenhouse gas emitting sectors with a significant proportion of agricultural emissions linked to soils. The Intergovernmental Panel on Climate Change (IPCC) calculates that all the carbon in lime, when added to agricultural soils to reduce acidity, is emitted as CO2, although some countries use a lower figure.

When lime is added to soil, it reacts with carbonic acid to create bicarbonate, calcium and magnesium. If there are strong acids present in the soil, such as nitric or sulfuric acid, these will react with the bicarbonate to create carbonic acid and release CO2.

Lead author Dr Tim Jesper Suhrhoff, from the Yale Centre for Natural Carbon Capture, said: “It is the reaction of acidity with the carbonate that creates CO2 emissions, not the addition of the lime itself. In the absence of the strong acids, the liming would not lead to any emissions and would actually remove CO2 from the atmosphere through the formation of bicarbonate.

“Current guidelines that penalise liming assume that if we didn’t lime, there would be no emissions, but that’s not the case. If we continue to add acidity to the soil, it will react with remaining natural pools of alkalinity to create emissions. By penalising liming, rather than the addition of acids, we are targeting the wrong driver and potentially losing the other benefits that liming can bring, in terms of increased yields and lower nitrous oxide emissions.”

The researchers use data from the Mississippi River basin, collected since 1900, to calculate the impact of atmospheric pollution, fertiliser use and liming on CO2 emissions. They show that the combination of industrial pollution from fossil fuel burning and increasing use of nitrogen fertilisers since the 1930s has created high levels of acidity in the soil which have not been counterbalanced by liming.

Since the 1930s, when limestone application to croplands substantially increased, both the efficacy and efficiency of carbon dioxide removal has also increased, as indicated by river records and model results. Researchers estimated that today removal is occurring at approximately 75% of the theoretical maximum rate.

The researchers call for a reconsideration of policy on agricultural emissions, with emissions being linked to addition of acid fertilisers rather than lime. However, they highlight this needs to be handled with care.

“We have known for a long time that liming is great for farmers and global food security,” says Dr Suhrhoff. “What we show here is that over longer timescales, it is also an efficient way to remove CO2 from the atmosphere. Adding a large amount of silicate rock to neutralise the acidity, before moving to liming, may be the best strategy to limit emissions and gain the additional benefits that liming can bring.”

The Goldschmidt Conference is the world’s foremost geochemistry conference. It is a joint congress of the European Association of Geochemistry and the Geochemical Society (US), and over 4000 delegates attend. It takes place in Prague, Czech Republic, from 6-11 July 2025.

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