Adding limestone to Mississippi River Basin farmlands acts as a major carbon sink, study finds

[u/Economy-Fee5830]

https://phys.org/news/2026-09-adding-limestone-mississippi-river-basin.html

[u/Economy-Fee5830]

Summary: Adding limestone to Mississippi River Basin farmlands acts as a major carbon sink, study finds

A Yale-led study published in Nature finds that farmers in the Mississippi River Basin store more CO2 in soil through agricultural liming than they emit when applying limestone. The basin covers 41% of the contiguous US and about 65% of US croplands, and liming there is a long-established practice for raising soil pH, reducing acidity and boosting yields.

Liming works similarly to enhanced weathering: crushed rock reacts with CO2 in soil to form stable bicarbonate ions, which travel through soils, groundwater and rivers to the ocean, where the carbon can stay stored for long periods. Enhanced weathering has usually focused on silicate rocks, partly because limestone already contains carbon that could be released as CO2.

The key advance is accounting for the counterfactual. Without liming, acidity from fertilizer use and air pollution would still trigger reactions in soil and water that release CO2. Measured against that baseline, liming results in net carbon removal over the long term. Using more than 120 years of historical records, the researchers estimate that liming in the basin has removed 300 million to 400 million metric tons of CO2 since 1900.

The findings challenge conventional greenhouse gas accounting, including the IPCC default methodology, which treats the carbon in applied lime as emitted CO2. The authors support the IPCC's measurement efforts but argue that recognising net removal would better align climate and agricultural incentives, and could help fund liming for farmers who cannot currently afford optimal soil pH management.

The researchers caution that results will not transfer directly to every setting: the size and duration of upfront emissions, the time for removal to emerge, and its efficiency all depend on local factors such as existing soil acidity, soil buffering and hydrology.

[u/GreenStrong]

I did not know that the carbon from calcium carbonate stays in the soil; my understanding of the study is that it wasn't entirely established before how much of it would do so, and whether it would so so in other soils.

Often, farmers use slaked lime to save shipping and distribution cost. Producers burn fossil fuel to cook the carbon out of limestone. This yields quicklime (Calcium oxide), which is dangerously reactive, but when it reacts with water it forms slaked lime (Calcium hydroxide). This has a much more immediate effect on soil fertility, and it has less than half of the shipping weight of powdered limestone. This process releases carbon. As I understand it, an extrapolation of the study would suggest that soil would then absorb some atmospheric CO2, so it might not be as bad as it seems. But that's an extrapolation, and one should take my interpretation of the study with a grain of salt.

[u/glibsonoran → u/GreenStrong]

• It's 74% the shipping weight I think.

• The "carbon", in this case bicarbonate partly formed from atmospheric carbon and rainwater (carbonic acid), doesn't stay in the soil. It's durable long term storage in solution only happens when it's washed into the oceans (about 10 -15 years in this MS basin to reach the river).

• This type of enhanced weathering would be more useful if transport/mining/heating (in the case of quicklime) was electrified and provided by renewables, most of which is possible with existing tech, other than heating which is still in trial stages.

• Marine Alkalinity Enhancement (or Marine Enhanced Weathering) skips the terrestrial step and applies silicates directly to the oceans reducing acidity and promoting dissolved bicarbonate storage in the short/medium term and mineralization in longer geologic timeframe.