Cover crop management: trade-off between carbon benefits, crop yield

A study led by researchers at the Agroecosystem Sustainability Center (ASC) at the University of Illinois Urbana-Champaign quantifies the soil organic carbon (SOC) benefits from cover crops in maize-soybean rotations in Midwestern U.S. agroecosystems.

The study, published in Global Change Biology, used ecosys, an advanced process-based ecosystem model, to assess the impacts of winter cover cropping on SOC accumulation under different environmental and management conditions. By understanding how SOC benefits can be achieved and optimized, farmers and policymakers will be able to enact management practices that support fertile fields that also sequester atmospheric carbon dioxide (CO₂) into the soil.

Cover crops have been found to be effective in increasing soil organic carbon by sequestering atmospheric CO₂ into the soil, and thus have large potential to mitigate climate change. An accessible method of measuring SOC benefits would help farmers, government agencies, and industries implement climate-smart cover cropping practices. However, an accurate and cost-efficient method of quantifying SOC benefits is still largely unavailable.

To help address this need, ASC researchers are taking an ecosystem modeling approach. Their study revealed that growing cover crops can increase SOC by an average of 0.33 megagrams of carbon per hectare per year (which is equivalent to 0.54 tons of atmospheric carbon dioxide per acre per year) in Illinois, and that SOC benefits can be improved through increasing cover crop biomass. The ecosys model not only helps quantify SOC benefits from cover crops, but also improves the scientific understanding of environmental factors that control on SOC benefits, including soil conditions, weather, and cover crop species.

Connecting with the team’s previous work, the researchers also found that there is a trade-off between SOC benefits from cover crops and cash crop yield. Specifically, if cover crops have larger growth windows, they grow larger biomass and thus have higher SOC benefits. However, under these circumstances, there is increased risk that the yield of cash crops is reduced due to the competition with cover crops for resources and nutrients including water, nitrogen, and oxygen in the soil; the work has been confirmed by a recent empirical study involving ASC members. Different lines of work collectively stress the need for careful cover crop management to avoid potential risks.

Comprehensive mechanistic modeling could help resolve this trade-off issue by simulating cover crop growth under different conditions. In U.S. Midwestern fields, management practices such as selecting specific cover crop types and regulating their growth window are major controlling factors of their SOC benefits. Through simulation, the modeling approach could help choose optimal management practices that maximize SOC benefits without compromising crop yield.

“Our study demonstrated that the ecosys model, with rigorous validation using field experiment data, can be an effective tool to guide the adaptive management of cover crops and quantify SOC benefits from cover crops,” said Ziqi Qin, lead author on the publication and graduate student in the U of I’s Department of Natural Resources and Environmental Sciences (NRES). “This provides practical tools and insights for practitioners to better manage cover crop and for policymakers to better design agricultural policies.”

In addition to SOC benefits, the researchers also found that cover crops could benefit the soil environment in other ways. The ecosys simulations indicated that the amount of carbon stored in microbes in the soil increased when cover crops were present. This finding is consistent with previous empirical studies that have found increased soil fertility when using cover crops.

“The optimal practices to manage cover crops vary for each field,” said ASC Founding Director Kaiyu Guan, NRES Associate Professor and also the project lead on the newly published study. “Our work identified the trade-off between cover crops and cash crops, which further proves the necessity to develop management guidance and technical assistance to farmers to better take advantage of cover crops while also maintaining cash crop yield.”

Co-authors on this study include U of I researchers Wang Zhou, Bin Peng, Tongxi Hu, María B. Villamil, Evan DeLucia, Andrew J. Margenot, Zhangliang Chen, and Jonathan Coppess; Jinyun Tang from DOE Lawrence Berkeley National Lab; Zhenong Jin from the University of Minnesota; Robert Grant from the University of Alberta; and Mishra Umakant from DOE Sandia National Lab.

This research was funded by the Illinois Nutrient Research & Education Council, NSF CAREER Award, USDA NIFA Program, and Foundation for Food and Agriculture Research.