Cellulosic biofuel potential of a winter rye double crop across the U.S. corn-soybean belt

Interest in renewable energy sources derived from plant biomass is increasing, raising concerns about fuel vs. food competition. One strategy to produce additional cellulosic biomass without reducing food-harvest potential is to grow winter cover crops after harvest of the primary summer crop. This study estimated biomass accumulation of a fall-planted winter rye (Secale cereale L.) double crop across the United States on corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] croplands. We identified corn and soybean areas by county using National Agricultural Statistics Service data, excluding irrigated land and areas already supporting a winter small-grain crop. Within this area, we calculated biomass production after corn harvest and before the subsequent corn or soybean crop for 30 locations using RyeGro, a cover-crop simulation model. Average RyeGro biomass yields for a 14-yr period were used to develop a regression model based on temperature and precipitation, which was used to determine rye biomass potential in each county. The spatial analysis indicated that 7.44 Mha in continuous corn and 31.7 Mha in a corn- soybean rotation are suitable for producing winter rye. The average RyeGro biomass yield for the 30 locations for six planting- harvest date scenarios is 4.2 Mg ha^-1. The regression modeling results projected that 112 to 151 Tg (120-170 million U.S. tons) of rye biomass can be harvested from this land base 14 to 7 d, respectively, before spring crop planting. The study demonstrates the sizable potential for this strategy to produce cellulosic biofuel feedstock without redirecting the primary food crop to fuel.