trade-off between carbon benefits, yields

A study led by researchers at the Center for Agroecosystem Sustainability (ASC) at the University of Illinois Urbana-Champaign quantified the soil organic carbon (SOC) benefits of cover crops in a corn-soybean rotation in a Midwestern US agroecosystem.

Studies published in Global Change Biologyused ecosys, an advanced process-based ecosystem model, to assess the impact of winter cover plantings on SOC accumulation under different environmental and management conditions. By understanding how SOC benefits can be achieved and optimized, farmers and policy makers will be able to put in place management practices that support arable land that also absorbs atmospheric carbon dioxide (CO2).₂) into the ground.

Cover crops have been shown to be effective in increasing soil organic carbon by sequestering atmospheric CO2₂ into the soil, and thus has great potential to mitigate climate change. An accessible method for measuring the benefits of SOC will help growers, government agencies and industry adopt climate-smart cover cropping practices. However, accurate and cost-effective methods for measuring SOC benefits are still largely unavailable.

To help address this need, ASC researchers are using 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 increased through increased covering plant biomass. That ecosys models not only help quantify SOC benefits from cover crops, but also enhance scientific understanding of the environmental factors that control SOC benefits, including soil conditions, weather, and cover crop species.

Linking to the team’s previous work, the researchers also found that there is a trade-off between the SOC benefits of cover crops and cash crop yields. In particular, if cover crops have a larger growth window, they grow a greater biomass and thus have higher SOC benefits. However, in these circumstances, there is an increased risk that cash crop yields are reduced due to competition with cover crops for resources and nutrients including water, nitrogen and oxygen in the soil; work has been confirmed by recent empirical studies involving ASC members. The different lines of work collectively stress the need for careful management of cover crops to avoid potential risks.

Comprehensive mechanistic modeling can help resolve this trade-off problem by simulating cover crop growth under different conditions. In US Midwestern fields, management practices such as selecting specific cover crop types and managing their growth window are major controlling factors for their SOC benefits. Through simulation, a modeling approach can help select optimal management practices that maximize SOC benefits without sacrificing crop yields.

“Our study shows that ecosys models, with rigorous validation using field trial data, can be effective tools to guide adaptive management of cover crops and quantify the SOC benefits of cover crops,” said Ziqi Qin, lead author of the publication and graduate student in the U of I Department of Natural Resources and Science. Environment (NRES). “It provides practical tools and insights for practitioners to better manage cover crops and for policy makers to better design agricultural policies.”

In addition to the benefits of SOC, the researchers also found that cover crops could benefit the soil environment in other ways. That ecosys Simulations show that the amount of carbon stored in microbes in the soil increases when there are cover crops. This finding is consistent with previous empirical studies that found improvements in soil fertility when using cover crops.

“Optimal practices for managing cover crops vary for each field,” said ASC Founding Director Kaiyu Guan, NRES Associate Professor and project leader on the newly published study. “Our work identified trade-offs between cover crops and cash crops, further demonstrating the need to develop management guidelines and technical assistance to smallholders to better utilize cover crops while maintaining cash crop yields.”

The study’s co-authors 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 of the DOE Lawrence Berkeley National Laboratory; Zhenong Jin of the University of Minnesota; Robert Grant of the University of Alberta; and Mishra Umakant of the DOE Sandia National Lab.

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