Climate change on course to hit U.S. Corn Belt especially hard, study finds

"It's important to begin thinking about how to transition out of our current damaging monoculture paradigm toward systems that are environmentally sustainable, economically viable for farmers and climate-smart," says Emily Burchfield, assistant professor in Emory's Department of Environmental Sciences.

By Carol Clark

Climate change will make the U.S. Corn Belt unsuitable for cultivating corn by 2100 without major technological advances in agricultural practices, an Emory University study finds. 

Environmental Research Letters published the research, which adds to the evidence that significant agricultural adaptation will be necessary and inevitable in the Central and Eastern United States. It is critical that this adaptation includes diversification beyond the major commodity crops that now make up the bulk of U.S. agriculture, says Emily Burchfield, author of the study and assistant professor in Emory’s Department of Environmental Sciences. 

“Climate change is happening, and it will continue to shift U.S. cultivation geographies strongly north,” Burchfield says. “It’s not enough to simply depend on technological innovations to save the day. Now is the time to envision big shifts in what and how we grow our food to create more sustainable and resilient forms of agriculture.” 

Burchfield’s research combines spatial-temporal social and environmental data to understand the future of food security in the United States, including the consequences of a changing climate. 

More than two-thirds of the land in the U.S. mainland is currently devoted to growing food, fuel or fiber. And about 80 percent of these agricultural lands are cultivated with just five commodity crops: Corn, soy, wheat, hay and alfalfa. Previous research based on biophysical data has established that climate change will adversely affect the yields of these crops. 

Building predictive models

For the current paper, Burchfield wanted to investigate the potential impacts of climate change on cultivation geographies. She focused on the six major U.S. crops that cover 80 percent of cultivated land in the United States: Alfalfa, corn, cotton, hay, soy and wheat. She drew from historical land-use data classifying where these crops are grown and publicly available data from the U.S. Department of Agriculture, the U.S. Geographical Survey, the WorldClim Project, the Harmonized World Soil Database and other public sources. 

Using these data, she built models to predict where each crop has been grown during the 20 years spanning 2008 to 2019. She first ran models using only climate and soil data. These models accurately predicted — by between 85 and 95 percent — of where these major crops are currently cultivated. 

Burchfield ran a second set of models that incorporated indicators of human interventions — such as input use and crop insurance — that alter biophysical conditions to support cultivation. These models performed even better and highlighted the ways in which agricultural interventions expand and amplify the cultivation geographies supported only by climate and soil. 

Burchfield then used these historical models to project biophysically driven shifts in cultivation to 2100 under low-, moderate- and high-emission scenarios. The results suggest that even under moderate-emission scenarios, the cultivation geographies of corn, soy, alfalfa and wheat will all shift strongly north, with the Corn Belt of the upper Midwest becoming unsuitable to the cultivation of corn by 2100. More severe emissions scenarios exacerbate these changes. 

“These projections may be pessimistic because they don’t account for all of the ways that technology may help farmers adapt and rise to the challenge,” Burchfield concedes. She notes that heavy investment is already going into studying the genetic modification of corn and soy plants to help them adapt to climate change. 

“But relying on technology alone is a really risky way to approach the problem,” Burchfield adds. “If we continue to push against biophysical realities, we will eventually reach ecological collapse.” 

The need for diverse landscapes

She stresses the need for U.S. agricultural systems to diversify beyond the major commodity crops, most of which are processed into animal feed. 

“One of the basic laws of ecology is that more diverse ecosystems are more resilient,” Burchfield says. “A landscape covered with a single plant is a fragile, brittle landscape. And there is also growing evidence that more diverse agricultural landscapes are more productive.” 

U.S. agricultural systems incentivize “monoculture farming” of a handful of commodity crops, largely through crop insurance and government subsidies. These systems take an enormous toll on the environment, Burchfield says, while also supporting a meat-heavy U.S. diet that is not conducive to human health. 

“We need to switch from incentivizing intensive cultivation of five or six crops to supporting farmers’ ability to experiment and adopt the crops that work best in their particular landscape,” she says. “It’s important to begin thinking about how to transition out of our current damaging monoculture paradigm toward systems that are environmentally sustainable, economically viable for farmers and climate-smart.” 

Burchfield plans to expand the modeling in the current paper by integrating interviews with agricultural policy experts, agricultural extension agents and famers. “I’d especially like to better understand what a diverse range of farmers in different parts of the country envision for their operations over the long term, and any obstacles that they feel are preventing them from getting there,” she says. 

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Paint color-matcher quantifies iron levels in soil

Debjani Sihi, right, demonstrates using the Nix Pro to measure iron content in soil with colleagues Gaurav Jha (left) and Biswanath Dari. Iron is a vital micronutrient to grow plants and "a fundamental mineral species that dictates many other soil functions, like carbon storage, greenhouse gas emissions and nitrogen and phosphorous recycling," says Sihi, a biogeochemist in Emory's Department of Environmental Sciences.  (Photo by Aneesh Chandel)
 

By Carol Clark

A handheld color-sensing tool, commonly used to match paint shades, is also effective at quantifying the iron content in soil by analyzing its color, a study finds. Agricultural & Environmental Letters published the research showing that the inexpensive color sensor, known as the Nix Pro, can rapidly and accurately quantify soil iron. 

“We found that the Nix Pro is easy to use in the field on soil samples and can give an accurate estimate for iron content within seconds using a technique that we developed,” says Debjani Sihi, corresponding author of the paper and assistant professor in Emory’s Department of Environmental Sciences. “We think that this device holds the potential to become a really handy, cost-effective tool for farmers.” 

Gaurav Jha, who did the work as a post-doctoral researcher at the University of California, Davis, is first author of the study. 

Iron is a vital micronutrient, explain Sihi, a biogeochemist who studies environmental and sustainability issues at the nexus of soil, climate, health and policy. Just as people need iron to make a protein in red blood cells that carries oxygen through the body, plants need iron to move oxygen through their systems and produce the chlorophyll that makes them a healthy, green color. 

Soil iron levels are also a key factor in climate change. “It’s a fundamental mineral species that dictates many other soil functions, like carbon storage, greenhouse gas emissions and nitrogen and phosphorus cycling,” Sihi says. 

And yet, iron is often deficient in soil, especially in agricultural lands. “If a farmer knows that their soil does not contain the right amount of iron for their crops, they can amend the soil before planting,” she says. 

Problems with testing for soil iron 

The problem farmers face is that determining iron content in soil is expensive and/or time consuming. One method is to gather soil samples from across a landscape. The samples are then sent to a laboratory for analyses via a benchtop atomic-absorption spectrometer or inductively coupled plasma. Laboratory analysis yields a precise percentage of iron content for each sample but it can be costly and often requires weeks to learn a result. 

A thick book of soil color samples, known as the Munsell charts, provides an alternative. Comparing the color of a soil sample with the swatches on the Munsell charts can guide an effort to classify the soil color. The downside to this method is that it requires practice, it is labor-intensive and the data is qualitative and imprecise. 

During a coffee break chat among Sihi, Jha and co-author Biswanath Dari, from North Carolina Agricultural and Technical State University, the idea came up of trying the Nix Pro’s color sensing on soil. 

The Nix Pro is a palm-sized light-emitting spectrometer that measures the reflectance of a surface to quantify its color composition. It’s commonly used by paint stores, printing shops and graphic design firms for color matching. A Nix Pro costs just $349 and is easy to use, with a cell phone app providing a near-instantaneous result for a sample. 

The Nix Pro soil sensor, center, is a handheld device that is more automated and user-friendly for measuring soil iron content than a book of color samples known as the Munsell charts. (Photo by Gaurav Jha)

“The color of soil can tell you a lot of stories about an environment,” Sihi says. 

Dark brown soil contains a lot of organic material while whitish soil indicates that most of the organic material has washed away. Dark red soil, including Georgia’s famous red clay, indicates strong iron-oxide content. 

If researchers want to learn about the water table in red clay soil, they can look at the colors in a cross-section of the ground. Past flooding will turn some of the soil layers from red to a grayish color because the water has washed out much of the iron. Tree roots from the past will appear as orange patches. “The orange color indicates where the tree roots borrowed oxygen from the surrounding air and oxidized the iron,” Sihi says. 

Sihi studies redox reactions involving electron receptors like oxygen and iron, which can reveal such hidden stories in an environment. Ferrous oxide, for instance, is known as iron 2 due to the number of electrons lost in the oxidation process. Ferric oxide, or iron 3, contains iron oxide that lost three electrons. 

Soil oscillating between periods of heavy rain to no rain undergoes fluctuating redux, or shifts in the levels of iron 2 and iron 3 as the water tables go up and down. “Fluctuating redox is a big threat multiplier for greenhouse gas emissions into the atmosphere,” Sihi says. 

‘An extremely strong result’ 

Due to the broad importance of iron, the researchers focused on iron content as the first soil test for the Nix Pro. They first collected data on soil samples from New Mexico using the Nix Pro app for three different color spaces: cyan, magenta, yellow and black; lightness and darkness; and red, green and blue. The Nix Pro app allowed them to export the data into an Excel document. 

Researchers from New Mexico State University helped calibrate and validate the three color models generated by the Nix Pro data by comparing them with results for total iron content generated through analysis in a NMSU laboratory. The results showed that all three of the models were significant in predicting soil iron content, with the cyan, magenta, yellow and black model (CMYB) delivering the strongest result. 

Finally, they further validated the CMYB model by using it to estimate total iron content in soil samples from an adjacent field. The results showed that the Nix Pro CMYB model was 80 percent accurate compared to laboratory results for the same samples. 

“That’s an extremely strong result,” Sihi says. “We’re comparing the power of a small, handheld tool with a really fancy lab instrument and it’s holding up.” 

The team now plans to test the Nix Pro on soils from other regions to determine if the method will work universally as an iron soil predicter. They hope other researchers will also apply their method to speed up the data-gathering process. Sihi and her colleagues plan to further expand their project by experimenting with the Nix Pro’s possible efficacy for other agricultural applications related to soil composition. And this summer, they will conduct a greenhouse gas experiment to evaluate if the Nix Pro color sensor can be used to identify nitrogen deficiency in corn plants through the characteristic symptom of yellowing leaves. 

Additional authors of the current paper include Harpreet Kaur, April Ulery and Kevin Lombard (NMSU); and Mallika Nocco (University of California, Davis). 

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Ancient DNA gives new insights into 'lost' Indigenous people of Uruguay

A sculpture commemorates the Indigenous people of Uruguay in the capital of Montevideo. Archeological evidence for human settlement of the area goes back 10,000 years. (Photo by Maximasu via Wikimedia Commons)

By Carol Clark

The first whole genome sequences of the ancient people of Uruguay provide a genetic snapshot of Indigenous populations of the region before they were decimated by a series of European military campaigns. PNAS Nexus published the research, led by anthropologists at Emory University and the University of the Republic, Montevideo, Uruguay. 

“Our work shows that the Indigenous people of ancient Uruguay exhibit an ancestry that has not been previously detected in South America,” says John Lindo, co-corresponding author and an Emory assistant professor of anthropology specializing in ancient DNA. “This contributes to the idea of South America being a place where multi-regional diversity existed, instead of the monolithic idea of a single Native American race across North and South America.” 

The analyses drew from a DNA sample of a man that dated back 800 years and another from a woman that went back 1,500 years, both well before the 1492 arrival of Christopher Columbus in the Americas. The samples were collected from an archeological site in eastern Uruguay by co-corresponding author Gonzalo Figueiro, a biological anthropologist at the University of the Republic. 

The results of the analyses showed a surprising connection to ancient individuals from Panama — the land bridge that connects North and South America — and to eastern Brazil, but not to modern Amazonians. These findings support the theory proposed by some archeologists of separate migrations into South America, including one that led to the Amazonian populations and another that led to the populations along the East coast. 

“We’ve now provided genetic evidence that this theory may be correct,” Lindo says. “It runs counter to the theory of a single migration that split at the foot of the Andes.” 

Archeological evidence 

The archeological evidence for human settlement of the area now known as Uruguay, located on the Atlantic coast south of Brazil, goes back more than 10,000 years. European colonizers made initial contact with the Indigenous people of the region in the early 1500s. 

During the 1800s, the colonizers launched a series of military campaigns to exterminate the native peoples, culminating in what is known as the massacre at Salsipuedes Creek, in 1831, which targeted an ethnic group called the Charrúa. At that time, the authors write, the term Charrúa was being applied broadly to the remnants of various hunter-gatherer groups in the territory of Uruguay. 

“Through these first whole genome sequences of the Indigenous people of the region before the arrival of Europeans, we were able to reconstruct at least a small part of their genetic prehistory,” Lindo says. 

The work opens the door to modern-day Uruguayans seeking to potentially link themselves genetically to populations that existed in the region before European colonizers arrived. “We would like to gather more DNA samples from ancient archeological sites from all over Uruguay, which would allow people living in the country today to explore a possible genetic connection,” Lindo says. 

Focusing on little-explored human lineages 

The Lindo ancient DNA lab specializes in mapping little-explored human lineages of the Americas. Most ancient DNA labs are located in Europe, where the cooler climate has better preserved specimens. 

Less focus has been put on sequencing ancient DNA from South America. One reason is that warmer, more humid climates throughout much of the continent have made it more challenging to collect usable ancient DNA specimens, although advances in sequencing technology are helping to remove some of these limitations. 

“If you’re of European descent, you can have your DNA sequenced and use that information to pinpoint where your ancestors are from down to specific villages,” Lindo says. “If you are descended from people Indigenous to the Americas you may be able to learn that some chunk of your genome is Native American, but it’s unlikely that you can trace a direct lineage because there are not enough ancient DNA references available.” 

Further complicating the picture, he adds, is the massive disruption caused by the arrival of Europeans given that many civilizations were destroyed and whole populations were killed. 

By collaborating closely with Indigenous communities and local archeologists, Lindo hopes to use advanced DNA sequencing techniques to build a free, online portal with increasing numbers of ancient DNA references from the Americas, to help people better explore and understand their ancestry. 

Co-authors of the current paper include Emory senior Rosseirys De La Rosa, Andrew Luize Campelo dos Santos (the Federal University of Penambuco, Recife, Brazil), Monica Sans (University of the Republic, Montevideo, Uruguay), and Michael De Giorgio (Florida Atlantic University). 

The work was funded by a National Science Foundation CAREER Grant. 

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