BOONE COUNTY, Iowa -- Adding diversity to corn-soybean rotations can provide higher yields and reduce the need for fertilizer, herbicide and fossil fuel inputs, according to a long-running research project supported by the Leopold Center for Sustainable Agriculture.
The project, begun in 2002 on Iowa State University’s Marsden Farm in Boone County, compares the conventional corn-soybean system with two alternatives, a three-year rotation that adds small grains with a red clover cover crop, and a four-year rotation that adds small grains and alfalfa hay. Matt Liebman, Iowa State University agronomy professor, leads the project.
Researchers found that “low-input, high-diversity” rotations outperform the conventional system in yields and produce similar profits. On average, corn yields in the diverse rotations were four percent greater and soybean yields nine percent greater. These results were achieved by replacing purchased inputs with combinations of ecological processes, human knowledge, production management skills and labor.
Liebman emphasized that yields remained high even during the transition years, an important consideration for farmers who want to diversify their cropland. The experiment showed that farmers can choose either genetically engineered or non-GE seeds and still receive superior yields compared to the conventional system.
Diverse rotations are less vulnerable to rising input costs, particularly fossil fuels. They consume approximately half the energy required annually by a conventional corn-soybean system. They also provide multiple environmental benefits, including:
- Synthetic nitrogen use reduced by 80-86 percent
- Effective weed control with 88 percent less herbicide
- Herbicide-related freshwater toxicity 200 times lower after nine years
The diverse rotations also likely reduce soil and nutrient loss, and potentially decrease the risk of creating herbicide-resistant weeds. “All these characteristics are aspects of increased system resilience,” Liebman said.
SOURCE: Leopold Center for Sustainable Agriculture