Rye as an energy cover crop: Management, forage quality, and revenue opportunities for feed and bioenergy

Authors: HERBSTRITT, STEPH - Pennsylvania State University; RICHARD, TOM - Pennsylvania State University; LENCE, SERGIO - Iowa State University; WU, HUAIQING - Iowa State University; O'Brien, Peter; Emmett, Bryan; KASPAR, THOMAS - Retired ARS Employee; KARLEN, DOUG - Retired ARS Employee; KOHLER, KEITH - Retired ARS Employee; Malone, Robert - Rob

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2022
Publication Date: 10/14/2022
Citation: Herbstritt, S., Richard, T.L., Lence, S.H., Wu, H., O'Brien, P.L., Emmett, B.D., Kaspar, T.C., Karlen, D.L., Kohler, K., Malone, R.W. 2022. Rye as an energy cover crop: Management, forage quality, and revenue opportunities for feed and bioenergy. Agriculture. 12(10). Article 12101691. https://doi.org/10.3390/agriculture12101691.
DOI: https://doi.org/10.3390/agriculture12101691

Interpretive Summary: Harvesting biomass from a winter rye cover crop could help meet growing demand for food and energy, while also improving environmental quality and farmer income. Winter rye can be used for animal feed, or it can be digested in a bioenergy system to produce renewable natural gas, which also creates residue that can be fed to animals as a protein concentrate. Using winter rye samples from Ames, Iowa, we studied 1) quality of animal feed, 2) income for farmers, and 3) greenhouse gas mitigation benefits of the fertilized rye used for animal feed or bioenergy production. For freshly harvested rye samples, feed value improved with fertilization. Digesting the winter rye improved forage quality compared to fresh rye. The income potential was highest with the digested double-cropped winter rye bioenergy system, which considered current prices for renewable natural gas, the high protein feed concentrate from the remaining residue, and greenhouse gas mitigation benefits. We found that the bioenergy system could more than capture and store the extra greenhouse gas emissions from fertilizing the winter rye, which suggests a positive environmental impact. This research will be of interest to producers and policy makers as a practice that can increase both farmer income and food and energy production on current cropland.

Technical Abstract: Harvesting biomass from a cover crop like winter rye (Secale cereale L.) could help sustain growing food and energy demand, provide new revenue streams and enhance ecosystem services without inducing land-use change. A two-year field experiment with three planting methods and three N fertilization rates that produced >5.0 Mg ha-1 yr-1 of biomass was evaluated for: 1) fresh and anaerobically digested rye forage quality; 2) revenue potential from freshly harvested rye and renewable bioenergy, carbon markets, and digestate feed protein; and 3) potential greenhouse gas (GHG) offsets. We showed that rye can be harvested as forage for animals or anaerobically digested to produce renewable natural gas (RNG), with the residue after digestion (digestate) still available as a feed protein concentrate. Livestock feed and soil carbon benefits of double cropping averaged $245 Mg-1 dry matter at current market prices. Compared to fresh rye, anaerobically digesting rye improved forage quality indicators. Digestion significantly decreased acid- and neutral-detergent fiber (ADF and NDF) by 5.2% and 17.8%, respectively, while significantly increasing CP (33.6%), total digestible nutrients (TDN) (2.0%), relative feed value (RFV) (23.6%), net energy for lactation (8.3%), maintenance (7.5%), and gain (20.0%). Using current market prices for RNG, high protein feed, and GHG mitigation, potential on-farm revenue averaged $546 Mg-1. Evaluation as an integrated system showed GHG emissions associated with rye fertilization and the overall carbon footprint of crop production were reduced, thus confirming the potential opportunity to sustainably intensify land use in the Midwestern United States.