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A comprehensive nine-year investigation has revealed that a more diversified three-year crop rotation that includes corn, cereal rye, soybean, and winter wheat can significantly decrease nitrogen runoff from agricultural fields without sacrificing crop yields. This study contrasts with the traditional two-year rotation of corn and soybean.
The findings have been published in the journal Frontiers in Environmental Science.
According to the researchers, drainage systems utilizing pipes known as tiles carry nitrogen, primarily in the form of nitrate, from agricultural fields to water bodies, leading to environmental degradation. This nitrate contamination poses a threat to streams and lakes that serve as drinking water sources for many communities. Additionally, it contributes to the expansive hypoxic area, or “dead zone,” in the Gulf of Mexico, exacerbated by nutrient runoff from major rivers like the Mississippi.
Lowell Gentry, a researcher in natural resources and environmental sciences at the University of Illinois Urbana-Champaign, explained the necessity of artificial drainage systems in Illinois for optimal crop production. However, he noted that these systems can lead to nitrogen loss through tile water. Thus, the objective of the research was to determine whether a more diverse crop rotation could mitigate nitrate loss from tiles while remaining competitive against the conventional corn-soybean rotation.
Over the course of the study from 2015 to 2023, the research team assessed crop yields and monitored nitrate levels from tile-drained fields on an operational farm. The control setup involved two fields adhering to a conventional rotation of corn and soybean, while an adjacent field followed the three-year system, alternating between corn, full-season soybeans, and winter wheat, followed by a double-crop of soybeans. To preserve soil integrity, a cover crop of cereal rye was cultivated between the corn and soybean phases, being terminated with herbicide before the soybean planting, allowing it to decompose and enrich the soil.
A notable divergence between the two methodologies was their approach to tillage. The control fields underwent full tillage during both the fall and spring, whereas the researchers applied strip-tillage to just a narrow strip of the cornfield in the three-year rotation, reducing overall tillage to one-third of the field every third year. “This method allows for a gradual tillage process over nine years,” Gentry explained, enhancing soil consistency and health.
Planting crops such as cereal rye and winter wheat in the fall post-harvest of corn and soybeans plays a crucial role in preserving soil structure, significantly reducing erosion and nitrate runoff. Gentry emphasized that tilling soil and leaving it uncovered during fall and winter periods fosters erosion and promotes the growth of beneficial microbes that consume organic matter, resulting in increased nitrate levels.
For years, agricultural stakeholders, including growers, policymakers, and researchers, have sought innovative methods to curb nitrate loss from farmlands. While some strategies involve woodchip bioreactors or artificial wetlands to capture runoff, these solutions often result in the loss of valuable nutrients.
“Producing fertilizer is costly; hence, it’s more strategic to conserve nitrogen and prevent it from leaving the fields,” remarked Gentry. “Cereal rye and winter wheat effectively absorb enough nitrogen during the colder months to lower the soil nitrate concentration, thereby reducing tile nitrate levels.”
The study observed a significant 50% decrease in tile nitrate losses with the three-year rotation in comparison to the traditional model, demonstrating that environmental benefits can be achieved without compromising agricultural productivity.
Continued funding from the Illinois Nutrient Research and Education Council supported this long-term project, allowing researchers to draw valuable conclusions. One year of unusual wet weather hindered the timely termination of the cereal rye cover crop, resulting in substantial biomass that lowered nitrate runoff by 90%. However, this oversaturation of rye led to a 10% decrease in soybean yield for that year. In another incident, an early freeze in the double-crop soybeans resulted in diminished yields and enhanced nitrate loss the following spring.
Gentry noted that conventional fields sometimes retained water after heavy rainfall, unlike the experimental fields, which lacked such standing water. “This is likely due to the reduced tillage in the experimental fields and the increased population of earthworms in the diverse rotation,” he stated. It’s noteworthy that both rotations employed the same conventional herbicide approach, indicating that tillage, rather than herbicide application, affects earthworm populations.
Preliminary assessments suggest that the economic viability of both cropping systems is comparable. Gentry concluded, “This research serves as a proof-of-concept, demonstrating that a more diverse rotation can sustainably enhance productivity while minimizing nitrate losses and improving soil quality, which could counteract the long-standing decline in organic matter across agricultural lands.”
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