Overly acidic soils can mean the difference between feeding a region and famine. Each crop needs the right soil pH to thrive, and acidic conditions, produced primarily by industrial emissions and application of fertilizers, can harm growing conditions. It has recently been estimated that sub-Saharan Africa, for example, loses billions of dollars annually in crop yield because of poor agricultural conditions. But there is a possible solution — and it could even help the Earth’s climate. 

For centuries, farmers have neutralized soil acidity with a practice called liming. It involves mixing crushed calcium- or magnesium-rich rocks, known as limestone, into the soil to balance pH. But liming has long been an assumed tradeoff in which removing acid also meant increasing carbon emissions into the atmosphere.

New research from Georgia Tech shows that the opposite may be true. Agricultural liming can actually reduce atmospheric carbon dioxide and improve crop yield. 

“The current thinking about liming is that farmers must choose between doing something that could benefit them economically or reducing their greenhouse gas emissions,” said Chris Reinhard, an associate professor in the School of Earth and Atmospheric Sciences. “But this is often a false choice. They can do both.”

The researchers published a new framework for the potential role of liming in food security and greenhouse gas mitigation in August in the paper, “Using Carbonates for Carbon Removal,” in Nature Water. 

Collecting Carbon Data

The framework is based in part on ongoing work Reinhard and his collaborators are pursuing on the impacts of agricultural liming in the Upper Midwest’s Corn Belt for a Department of Energy study. With funding from the Grantham Foundation, they’re now turning their attention to local farms in southern Georgia and North Carolina. 

For each farm, the researchers measure data that most farmers would collect already, like soil pH and nutrients. But the team also tracks more specialized measurements, including trace elements and greenhouse gas fluxes in the soil. All this data is matched to a high-resolution, machine learning grid of the farm’s geography to determine exactly which crops might benefit. 

The researchers are using the data to build a computer model that predicts how carbon dioxide and other greenhouse gases will move through any particular soil system. Liming won’t universally absorb carbon dioxide — or if it does, there may be an occasional time delay between carbon emissions and absorption — which is why the researchers factor soil, crop rotation, climate, and other management practices into their calculations.

“Our goal is to develop a way that farmers can monitor and plan cheaply, and largely through techniques they are already using, so we don't have to send out a whole team to gather data,” Reinhard said. “We are trying to develop a predictive model architecture for planning agricultural practice across scales, but it’s important that the techniques required on the field are actually feasible for farmers.”

This data could be pivotal for farmers, and it could also help policymakers as they address farming subsidies and foreign aid funding. Globally, food-insecure regions like sub-Saharan Africa could become more self-sufficient with more liming. Farmers in parts of the U.S. could also improve their yields and, in effect, their profits, if they limed more fields. 

The added benefit of lowering carbon could get even more farmers on board, and there is extensive exploration and implementation of agricultural practices already on voluntary and governmental carbon markets. Carbon dioxide is only one greenhouse gas that liming can lower; researchers are also exploring how liming can reduce methane and nitrous oxide — the latter of which is a key climate impact of human agriculture and is often considered a “hard-to-abate” emission. 

Liming may be a centuries-old practice, but its applications are potentially much wider than initially believed. In the future, farming may be part of the answer to reducing carbon emissions, instead of part of the problem.