In the rich black soil outside Decatur, Illinois, a quiet experiment is unfolding beneath the feet of a former cornfield. After 180 years of growing maize — the crop that feeds cattle, fills gas tanks, and lines supermarket shelves — the earth here has lost roughly half the carbon it once held. Now, scientists are finding, that carbon is creeping back.
A team from the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), a research center focused on turning plants into fuel and useful materials, planted rows of miscanthus and switchgrass — tall perennial grasses that grow back year after year without needing to be replanted — on old corn and soybean fields across Illinois. What they discovered, published in the journal Geoderma, offers a glimmer of hope for soil health across the American Midwest.
The researchers measured carbon stored in the top meter of soil at seven sites, comparing fields where they had recently planted the bioenergy grasses with land still farmed with annual maize and with patches of native tallgrass prairie that had never been plowed. The numbers told a clear story: native prairie held about 146 metric tons of carbon per hectare, while active cornfields held only about 88 metric tons per hectare. But fields growing miscanthus held 107 metric tons per hectare, and switchgrass fields held roughly 98 metric tons per hectare — both pulling closer to prairie levels.
After just five years, carbon levels had already begun climbing at four of the seven bioenergy crop sites. The team used carbon isotope analysis to confirm the new carbon was coming from the grasses themselves, not from elsewhere. This matters because annual crops like corn and soy must be planted, tilled, and harvested every year, a cycle that exposes soil to air and causes stored carbon to escape. Perennial grasses, by contrast, keep their roots in the ground for many seasons, steadily pumping fresh organic matter into the earth.
Lead author Ilsa B. Kantola and her colleagues acknowledged that full restoration to pre-farming prairie levels would likely take decades, even with decades more growth. But the early gains suggest that switching even some corn acreage to perennial bioenergy grasses could chip away at a regional carbon deficit built up over nearly two centuries. For farmers weighing whether to grow crops for fuel instead of food, the added benefit of soil improvement may tip the scales — healthier soil holds more water, grows better crops, and erodes less in heavy rain.
The Midwest holds some of the world's most productive farmland, and also some of its most depleted soils. This research suggests that what was lost to the plow might be slowly, stubbornly regained by the root.