This page provides supporting information (SI) prepared for the manuscript "Winter rye biomass can be an abundant and affordable US energy resource." It summarizes research developed through collaboration between USDA and Penn State winter rye subject matter experts and economists from ORNL's Bioresource Science and Engineering Group.
We obtained 14-year average winter rye yield simulations from the RyeGro soil-plant-atmosphere model previously developed for 30 US locations and six planting and harvesting date scenarios (Feyereisen et al. 2013). We used county-level regression model yields for the scenarios where cereal rye is planted 2 days after the prior corn grain or soybean harvest, and the subsequent corn or soybean crop is planted 7 days after the rye harvest on land in continuous corn and corn/soy rotation. These county-scale winter rye yields were inputs (SI.1) for the POLYSYS economic model (Ugarte and Ray 2000) used to estimate future agricultural biomass supplies for the DOE 2023 Billion-Ton Report (DOE 2024). Regional agronomic budget inputs (e.g., fertilizer and seeding rates, labor and machinery costs) were developed based on Malone et al. (2023) and the assumption that rye would be harvested and hauled wet in a wagon to an on-farm pit or silage bunker rather than being baled (SI.2).
Modeled fertilizer applications were 45 kg/ha of N, 15 kg/ha of P, and 56 kg/ha of K (41 lbs/acre of N, 13 lbs of P and 50 lbs/ac of K). The N fertilizer application rate was based on results from several studies across 6 states in the midwestern and southeastern US where responses to N fertilization rates from 0 to 120 kg/ha were mixed (Malone et al. 2022; Malone et al. 2023, Crespo et al. 2025; Balkcom et al. 2018). In a 13-year randomized plot trial, Crespo et al. (2024) observed that winter rye shoot biomass responded to both warmth (growing degree days) and precipitation. In a two-year trial with adequate rainfall both years, Crespo et al. (2025) observed that rye responded more to warmer spring temperatures than to N fertilizers. In a cool spring with yields < 3 Mg/ha supplemental N fertilization did not improve yields compared with natural N mineralization from soil organic matter (0 fertilizer N), but in a warmer spring when there were sufficient growing degree days, supplemental N fertilizer at 30 and 60 kg N/ha resulted in higher yields. While we used the midpoint of 30 and 60 kg/ha (45 kg N/ha) for this study’s national projections, location-specific fertilizer recommendations should be based on local climate and soil conditions.
Western US counties where evaporation exceeds precipitation were excluded from consideration since our budgets do not account for irrigation; unirrigated rye in these areas would consume soil water needed for corn and soybeans. In the eastern US with ample spring soil water, we assumed rainfed winter rye even if the summer crop is irrigated; so winter rye was allowed in these counties if profitable given county yields and costs.
We started POLYSYS with the 2023 USDA agricultural baseline and ran the model out to 2041 with annual timesteps and price intervals to simulate a mature market demand for biomass. Winter rye production was limited to locations where the net returns of corn/rye/soy rotations were greater than the net returns from corn/soy rotations. County-level biomass estimates (SI.3) and production areas (SI.4) are summarized here for three biomass farmgate rice offerings in dollars per dry US short ton: $30/dt, $70/dt, and $150/dt. At a price offering of $150/dt ($165/Mg), we found a potential winter rye biomass supply of 214 M dry short tons (194 million Mg) produced across 80.7 million acres (32.7 million ha).
We modeled winter rye production relative to a “pessimistic case” of 10% lower rye yields and 10% higher production costs relative to an “optimistic case” of 10% rye yield improvements and 10% lower production costs (SI.5). With improvements in crop yield and harvesting efficiency, winter rye biomass production could increase to 230 million Mg yr-1. We then compared the economic returns and acreages of winter rye to other bioenergy crops and residues recently modeled for DOE's national biomass resource assessment. We found that winter rye is competitive with other cellulosic feedstocks across a range of prices and can produce more biomass at a lower cost than perennial grasses (switchgrass and miscanthus), crop residues (corn stover and wheat straw), and woody biomass (poplar and willow) (SI.5).
Because this crop is grown on land that would otherwise be fallow, we found that high price offerings and large volumes of winter rye would have little or no impact on national 20-year average equilibrium food crop prices (SI.6). Winter rye is easier to establish and remove than perennial crops like miscanthus or willow, meaning that it has lower risk and is more likely to expand across acres than other dedicated energy crops (SI.7).
We calculated energy and fertilizer yields from the potential 194 million Mg annual biomass supply at a price offering of $165/Mg by assuming the rye was anaerobically digested to produce renewable natural gas (RNG). We used previously published biogas production rates (Herbstritt et al. 2022) and calculated net energy based on both agronomic and digester operations as well as an average round trip transportation distance of 129 km to a centralized digester (SI.2). For this biomass production quantity, annual bioenergy yields would be 1.59 EJ per year (SI.8). If all of this winter rye were converted to natural gas through anaerobic digestion, we estimate that there would be enough nitrogen in the digestate to recover 1.3 million Mg of N fertilizer (SI.8).
The 8 referenced file attachments of supporting information (SI) are provided below the Citations. Additional POLYSYS outputs for the Winter Rye scenarios exceed the 8 MB file size limit for this site but are available upon request. Please contact biokdfadmin@ornl.gov for access.
Citations:
Balkcom, K.S., Duzy, L.M., Arriaga, F.J., Delaney, D.P. and Watts, D.B. (2018), Fertilizer Management for a Rye Cover Crop to Enhance Biomass Production. Agronomy Journal, 110: 1233-1242. https://doi.org/10.2134/agronj2017.08.0505.
Crespo, C., Malone, R. W., Radke, A., Kovar, J. L., Emmett, B. D., Feyereisen, G. W., Thorp, K. R., Richard, T., & O'Brien, P. L. (2025). Rye performance in central Iowa under different seeding and nitrogen fertilizer rates. Agronomy Journal, 117, e70112. https://doi.org/10.1002/agj2.70112.
Crespo, C., O’Brien, P. L., Ruis, S.J., Kovar, J.L., Kaspar, T.C. (2024). Thermal time and precipitation dictate cereal rye shoot biomass production, Field Crops Research 315, https://doi.org/10.1016/j.fcr.2024.109473.
Feyereisen, G. W., G.T.T. Camargo, R.E. Baxter, J.M. Baker, and T.L. Richard (2013). Cellulosic biofuel potential of a winter rye double crop across the US corn-soybean belt. Agronomy Journal 105(3):631-642.
Herbstritt S., T. L. Richard, S. H. Lence, H. Wu, P. L. O’Brien, B. D. Emmett, T. C. Kaspar, D. L. Karlen, K. Kohler, and R. W. Malone (2022). Rye as an energy cover crop: management, forage quality, and revenue opportunities for feed and bioenergy. Agriculture 12:1691.
Malone, R.W., O’Brien, P.L., Herbstritt, S., Emmett, B.D., Karlen, D.L., Kaspar, T.C., Kohler, K., Radke, A., Lence, S.H., Wu, H., and Richard, T.L. (2022). Rye soybean double-crop: planting method and N fertilization effects in the North Central US. Renewable Agriculture and Food Systems 1–12. https://doi.org/10.1017/S1742170522000096
Malone R.W., A. Radke, S. Herbstritt, H. Wu, Z. Qi, B. D. Emmett, M. J. Helmers, L. A. Schulte, G. W. Feyereisen, P. L. O’Brien, J. L. Kovar, N. Rogovska, E. J. Kladivko, K. R. Thorp, T. C. Kaspar, D. B. Jaynes, D. L. Karlen, and T. L. Richard (2023). Harvested winter rye energy cover crop: Multiple benefits for North Central US. Environmental Research Letters 18:(7), 074009.
Ugarte D.G. and D. E. Ray (2000). Biomass and bioenergy applications of the POLYSYS modeling framework. Biomass and Bioenergy 18(4), 291-308.
US Department of Agriculture (USDA). Agricultural Projections to 2034. Office of the Chief Economist, World Agricultural Outlook Board, US Department of Agriculture. Prepared by the Interagency Agricultural Projections Committee. Long-Term Projections Report OCE-2025-1, 114 pp. (2025).
US Department of Energy (DOE). 2023 Billion‐Ton Report: An Assessment of US Renewable Carbon Resources. M. H. Langholtz (Lead). Oak Ridge, TN: Oak Ridge National Laboratory. ORNL/SPR-2024/3103 (2024). https://www.energy.gov/eere/bioenergy/2023-billion-ton-report-assessmen…
US Department of Agriculture (USDA). Agricultural Projections to 2034. Office of the Chief Economist, World Agricultural Outlook Board, US Department of Agriculture. Prepared by the Interagency Agricultural Projections Committee. Long-Term Projections Report OCE-2025-1, 114 pp. (2025).