Cropland expansion research

Cropland expansion (other land converted to cropland) and abandonment (cropland converted to non-cropland) in the U.S. Western Corn Belt during (a) 1980-2005 and (b) 2006-16 from trajectory analysis of the cropland data layer (CDL), and Yu and Lu (2018). Purple line shows the boundary of the U.S. Prairie Pothole Region (PPR).

AMES, Iowa — Faster conversion of land into agricultural production in recent years has raised the region’s carbon cost of producing grains, according to recently published research from an Iowa State University scientist.

The study, published in the academic journal Environmental Research Letters, shows that increases in crop production due to expanding acreage devoted to agriculture in five Midwestern states between 2006 and 2016 has reduced the region’s soil carbon content, according to an Iowa State University news release.

The reduced carbon storage capacity means that some carbon that once resided in the soil and plant life is released into the atmosphere instead.

“When people think of land-use changes with environmental and climate consequences, much attention has been paid to tropical deforestation or drained peatlands,” said Chaoqun Lu, an assistant professor of ecology, evolution and organismal biology and lead author of the study. “Intensive and extensive farming in the U.S. Corn Belt can have environmental and climate outcomes that demand our consideration as well.”

Crop production must grow in order to meet rising global demand for food, Lu said. Meeting that demand will require either what the researchers call “intensive” farming practices that will increase yields per acre, or “extensive” farming practices that will expand the available acres for cultivation, or both.

Studies across the world have argued that expanding cropland for additional production may lead to loss of plant and soil carbon and threaten the survival of wildlife. That’s because newly expanded cultivation usually clears land, disturbs the soil and releases carbon stored in the ground, she said.

The researchers used an index of agricultural carbon footprint to measure the carbon cost of per-unit grain production and the reasons responsible for its change in the Western Corn Belt. The study shows those changes factored into the region’s grain production shifting from carbon neutral to carbon loss during the most recent decade, meaning the region emits more carbon when producing per unit of grain than it did in previous decades.

The study found that for every kilogram of additional grain yield added during the 2006-16 period, the region’s soil lost 2.3 kilograms of carbon.

The study analyzed satellite products and reconstructed historical data on land use changes in Iowa, Minnesota, South Dakota, North Dakota and Nebraska over a period of decades. The researchers then used a computer-based ecosystem model to distinguish and quantify how land use, agricultural management practices and natural drivers such as climate change have affected crop production as well as carbon storage.

Lu said the study found the area of natural vegetation converted to agricultural production tripled during the decade between 2006 and 2016 compared to the period between 1980 and 2005. Much of those land use changes occurred in the Dakotas and Minnesota as grasslands and wetlands were converted into farm fields, Lu said.