Harvested winter rye energy cover crop: multiple benefits for North Central US

Authors: Malone, Robert - Rob; Radke, Anna; HERBSTRITT, STEPH - Pennsylvania State University; WU, HUAIQING - Iowa State University; QI, ZHIMING - McGill University - Canada; Emmett, Bryan; HELMERS, MATT - Iowa State University; SCHULTE, LISA - Iowa State University; Feyereisen, Gary; O'Brien, Peter; Kovar, John; Rogovska, Natalia; KLADIVKO, EILEEN - Purdue University; Thorp, Kelly; KASPAR, TOM - Retired ARS Employee; JAYNES, DAN - Retired ARS Employee; KARLEN, DOUGLAS - Retired ARS Employee; RICHARD, TOM - Pennsylvania State University

Submitted to: Environmental Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2023
Publication Date: 6/16/2023
Citation: Malone, R.W., Radke, A.G., Herbstritt, S., Wu, H., Qi, Z., Emmett, B.D., Helmers, M., Schulte, L., Feyereisen, G.W., O'Brien, P.L., Kovar, J.L., Rogovska, N.P., Kladivko, E.J., Thorp, K.R., Kaspar, T., Jaynes, D.B., Karlen, D., Richard, T. 2023. Harvested winter rye energy cover crop: multiple benefits for North Central US. Environmental Research Letters. 18(7). https://doi.org/10.1088/1748-9326/acd708.
DOI: https://doi.org/10.1088/1748-9326/acd708

Interpretive Summary: Cover crops can improve the environment by reducing nitrogen (N) loss to shallow groundwater and subsurface drainage. Cover crops also have potential as a valuable energy crop when harvested as a bioenergy feedstock for renewable natural gas production, which can occur without competing with food crops for land use. A regional assessment for the North Central (Upper Midwest) US is needed to quantify the potential benefits of this practice. We studied corn-soybean rotations with and without winter rye energy cover crops across a five-state area (MN, IA, IL, IN, and OH) with counties in the Mississippi River Basin. Harvesting fertilized rye energy cover crops before soybean planting in this area can reduce N loads to the Gulf of Mexico by 216 million kg per year or 27% relative to no cover crops and provide 18 million metric tons per year of biomass. This biomass could produce bioenergy equivalent to four times the 2022 US cellulosic biofuel production, which has multiple benefits compared to corn- and fossil-based energy production. During renewable natural gas production with rye biomass, the carbon dioxide could be inexpensively captured and stored in underground geologic reservoirs, removing 7.5 million metric tons of carbon dioxide per year. These results suggest that large-scale energy cover crop adoption would substantially contribute towards the goals of reducing N loads to the Gulf of Mexico, increasing bioenergy production without reducing food production, and providing carbon benefits such as removing carbon dioxide from the atmosphere. These findings are important to producers, scientists, crop advisers, and policy makers trying to find the best agricultural management practices in the North Central U.S.

Technical Abstract: Cover crops can reduce nitrogen (N) loss to subsurface drainage and be reimagined as bioenergy crops for renewable natural gas production and carbon (C) benefits (fossil fuel and carbon dioxide (CO2) offsets and C storage). Little information is available on the impacts of large-scale adoption of winter rye for these purposes. To investigate the impacts in the North Central US, we used the Root Zone Water Quality Model (RZWQM) to simulate corn-soybean rotations with and without winter rye across 40 sites. The simulations were interpolated across a five-state area (MN, IA, IL, IN, and OH) with counties in the Mississippi River Basin consisting of approximately 8 million ha with potential for rye cover crops on artificially drained corn-soybean fields (more than 63 million ha total). Harvesting fertilized rye cover crops before soybean planting in this area can reduce N loads to the Gulf of Mexico by 27% relative to no cover crops, and provide 18 million Mg/year of biomass–equivalent to 0.21 exajoule/year of biogas energy content or four times the 2022 US cellulosic biofuel production. Capturing the CO2 in biogas from digesting rye in the region and sequestering it in underground geologic reservoirs could mitigate 7.5 million Mg CO2/year. Nine hot spots were identified as an example of implementing rye as an energy cover crop on an industrial scale, consisting of roughly 20% of the region's area while providing ~50% of the benefits. These results suggest that large-scale energy cover crop adoption would substantially contribute towards the goals of reducing N loads to the Gulf of Mexico, increasing bioenergy production, and providing C benefits.