An Iowa State University study reveals soybeans are responsible for 40% of nitrous oxide emissions in corn-soybean rotations. Researchers propose practical, scalable solutions to cut emissions and boost yields.
In Iowa’s iconic two-year crop rotation of corn and soybeans, soybeans contribute a surprising 40% of nitrous oxide emissions, according to a study by Iowa State University researchers. This potent greenhouse gas, with 300 times the heat-trapping power of carbon dioxide, underscores the need for fresh approaches to sustainable farming.
“We’ve just been assuming that legume crops like soybeans don’t have a big emissions footprint because they don’t usually receive fertilizer,” said Michael Castellano, agronomy professor at Iowa State University, in a recent ISU news release. “But the natural processes in soil that produce nitrous oxide don’t stop just because you don’t apply fertilizer. Nearly half of our emissions in a typical cropping system come from soybeans, and we haven’t even been thinking about how to manage them.”
The Unexpected Culprit: Soybeans
Soybeans are typically considered environmentally friendly since they don’t require nitrogen fertilizers. However, Iowa State’s findings challenge that assumption. When microbes break down organic matter in soil, nitrogen is released, and without plants to use it, the nitrogen becomes nitrous oxide gas.
“It’s coming from biochemical processes we can’t do anything to stop,” said postdoctoral researcher Tomas Della Chiesa.
This process intensifies in spring when bare fields warm up and microbial activity spikes, contributing to substantial nitrous oxide emissions.
A Two-Pronged Solution
Castellano and Della Chiesa’s paper in Nature Sustainability proposes strategies to cut soybean-year emissions by one-third while increasing yields by 16%. The researchers suggest:
- Planting Winter Cover Crops: Oats or rye sown into mature corn fields protect soil during the offseason.
- Earlier Soybean Planting: Using extended-growth soybeans allows earlier planting and longer growing seasons.
“My favorite part of this research is farmers are more likely to implement these solutions right away because they’re practical and scalable,” Castellano said.
A Path Forward
The United Soybean Board has funded a three-year follow-up study testing these solutions in experimental plots across Iowa, Illinois, Minnesota, and Kentucky. Early results show promise in reducing emissions and improving yields.
Additionally, Iowa State researchers are exploring early planting’s emissions impact on corn and genetic improvements to make crops more tolerant to early-season cold.
“Emissions from agriculture as a proportion of global emissions are expected to go up rapidly,” Castellano said. “So we need these reduction strategies.”
