Biomass sorghum could qualify as a cellulosic biofuels feedstock under the Renewable Fuel Standard, according to a preliminary analysis by the U.S. Environmental Protection Agency.
EPA opened a 30-day public comment period on the analysis Dec. 31, available at regulations.gov. The EPA analysis said the greenhouse gas emissions profile of sorghum is virtually the same as switchgrass. According to USDA’s National Agriculture Statistics Service, 7.2 million acres were planted to sorghum in 2014 and 6.2 million acres harvested. The United States produced more sorghum than any country at nearly 10.4 million metric tons in 2014.
Grain sorghum isn’t widely used to produce ethanol in the U.S. There are just 10 plants that list sorghum as at least a partial feedstock, according to the Renewable Fuels Association. However, the emergence of sweet sorghum and other potential varieties could provide a significant market for U.S. farmers in an emerging cellulosic biofuels industry and the proposed pathway is thought to be part of the key to provide that spark.
EPA approved pathways for grain sorghum as an advanced biofuel feedstock in the RFS in December 2012. In the latest analysis, EPA looks at sweet sorghum, forage sorghum, and at efforts to breed new sorghum for increased biomass content.
“Our preliminary assessment indicates that on a per-dry-ton of feedstock basis (for biomass sorghum) indirect land use emissions would be lower, direct emissions associated with use of farm machinery, fertilizers and pesticides would be lower, and that emissions associated with feedstock transport would be the same as for switchgrass,” EPA said in the analysis.
The wide array of sorghum varieties available, EPA said, makes it difficult to create a cellulosic biofuels pathway.
“Differentiating the types of sorghum for purposes of the lifecycle analysis required under the RFS program is challenging because varieties bred for different purposes all belong to the same species and are often defined based on end-use, rather than based on specific physical characteristics,” the agency said. “For purposes of this notice, EPA considers biomass sorghum to be sorghum bicolor that has been selected or bred to maximize cellulosic content rather than sugar or grain content, and which therefore has at least 75% cellulosic content.”
EPA said it also considers hybrids that are crosses of sorghum bicolor and Sudangrass to be biomass sorghum if they have 75% cellulosic content, “but EPA does not consider hybrids that are crosses of sorghum bicolor and Johnsongrass (sorghum halepense) to be biomass sorghum, even if such hybrids have 75% or higher cellulosic content. This approach is consistent with the NSP petition, which explicitly excluded Johnsongrass due to concerns regarding its potential to behave as an invasive species.”
In analyzing the GHG emissions from biomass sorghum production, EPA examined crop yields and production inputs compared to switchgrass. The agency said sorghum can provide much higher weight per acre.
“For the switchgrass lifecycle analysis, EPA assumed national average yields of approximately 4.5 to 5 dry tons per acre,” EPA said. “Based on field trials in nine states under a range of growing conditions, the 2012 average yield of sorghum grown for biomass content is approximately 11 dry tons per acre, suggesting that biomass sorghum will have significantly higher yields than switchgrass.”
In addition, the agency said it built in expected improved yields in the analysis. “EPA anticipates similar yield improvements for biomass sorghum as for switchgrass since both feedstocks are energy crops in the early stages of development, and improvements in farming practices or new hybrids could increase the yield over time,” EPA said. “Given the potential for yield improvements, our analysis assumed an average biomass sorghum yield of 13 dry tons per acre in the southern United States by 2022, which was calculated using a 2% annual increase in yield.”
Because of its higher yield, biomass sorghum grown in areas with suitable growing conditions would require about 50% less land area compared to switchgrass to produce the same amount of biomass, the agency said.
“Biomass sorghum is not currently grown at commercial scale in the United States for the purpose of biofuel production, although approximately 1.4 million acres of forage sorghum were planted in 2012,” EPA said. “Biomass sorghum is currently grown in test plots as part of research to develop it as an energy crop, and currently has no other uses. Biomass sorghum can be planted as early as April and can continue growing until the fall.”
The agency said biomass sorghum production is expected to be concentrated in Texas, Oklahoma and Kansas, as well as in Missouri and Arkansas. EPA said it believes there is land area adequate enough to grow biomass sorghum for biofuels.
EPA said it believes indirect land use change GHG emissions associated with biomass sorghum would “likely be smaller than such emissions for switchgrass. Thus, we believe that our proposal to assume in our lifecycle GHG emissions assessments that indirect land use change GHG emissions from biomass sorghum would be similar to switchgrass represents a conservative approach.”
For biomass sorghum biofuels to qualify as cellulosic biofuel in the RFS program, the fuel must achieve a 60% lifecycle GHG reduction as compared to the 2005 baseline fuels. In addition, the biofuels must also be derived from cellulose, hemicellulose and lignin.