Sorghum should be in the biofuel crop mix, experts say

The scientists from Purdue, the University of Nebraska-Lincoln, University of Illinois and Cornell University believe sorghum, a grain crop similar to corn, could benefit from the rail system, grain elevators and corn ethanol processing facilities already in place. Their perspective article is published early online in the journal Biofuels, Bioproducts & Biorefining.

"The Midwest is uniquely poised to get the biorefining industry going on cellulose," said Nick Carpita, a Purdue professor of botany and plant pathology. "As we move to different fuels beyond ethanol, the ethanol plants of today are equipped to take advantage of new bioenergy crops."

The scientists argue that no single plant is a silver-bullet answer to biofuels, but sorghum should be a larger part of the conversation than it is today. Cliff Weil, a Purdue professor of agronomy, said some types of sorghum would require fewer inputs and could be grown on marginal lands.

"In the near future, we need a feedstock that is not corn," Weil said. "Sweet and biomass sorghum meet all the criteria. They use less nitrogen, grow well and grow where other things don't grow."

The ability to minimize inputs such as nitrogen could be a key to sorghum's benefits as a bioenergy crop. Carpita said corn, which has been bred to produce a maximum amount of seed, requires a lot of nitrogen. But sorghum could be genetically developed in a way that maximizes cellulose, minimizes seeds and, therefore, minimizes inputs.

"If you're just producing biomass and not seed, you don't need as much nitrogen," Carpita said.

Farmers may also be more willing to grow sorghum -- a crop they're familiar with -- because it is an annual, compared with perennials such as switchgrass or Miscanthus, that would take up a field for a decade or longer. Sorghum would fit in a normal crop rotation with food crops rather than tying up valuable cropland.

"If we're talking about planting switchgrass, that's a 15-year commitment," said Nathan Mosier, a Purdue associate professor of agricultural and biological engineering. "You can't switch annually based on the economy or other factors. You are committed to that crop."

Conversion processes for turning biomass into fuel need to be scalable and take advantage of existing infrastructure for grain production, said Maureen McCann, a Purdue professor of biology and director of the Energy Center and the Center for Direct Catalytic Conversion of Biomass to Biofuels. Sorghum could be harvested and transported using existing rail lines to collection points such as grain elevators, where the crop could be processed to a higher-value, more energy-dense product before being transported for further processing in a refinery.

"Biomass has roughly half the energy content of gasoline -- even if it's very compressed and tightly packed. The issue is really how to increase the intrinsic energy density by preprocessing conversion steps that could be done on farm or at the silo so that you're transporting higher-energy products to the refineries," McCann said.

Farzad Taheripour, a Purdue research assistant professor of agricultural economics, said bringing sorghum back as a biofuel crop could have an economic impact on poorer rural areas of the country.

"Given that sorghum can be produced on low-quality, marginal lands in dry areas, producing sorghum for biofuel will significantly improve the economy of rural areas that rely on low-productivity agriculture," Taheripour said. "This could improve welfare in less-developed rural areas and increase job opportunities in these areas."

Purdue Agriculture researchers are continuing to look at how bioenergy crops could be deployed into the agricultural landscape. Work in the Center for Direct Catalytic Conversion of Biomass to Biofuels continues to develop a knowledge base for chemical and thermal conversion technologies that might be able to take advantage of the Midwest's transportation infrastructure.