What is in this article?:
- Known as the sugarcane of the desert, sweet sorghum could be a sustainable and ecological future biofuel crop for Arizona.
- Sweet sorghum is easier to process into ethanol than corn or other grain crops.
- When it comes to developing a biofuel industry based on sugar-producing crops such as sweet sorghum, Arizona – and much of the desert Southwest – has what it takes.
Why sorghum? "It's a drought-tolerant, salt-tolerant, tough crop," said Slack. "Sorghum would be a preferred crop in a hot, arid region." This autumn, the researchers reaped their most successful harvest to date, gathering 16 plots worth of four different varieties of sorghum.
Said Slack: "This year we're looking at four different varieties: The traditional one, which is the M81E developed at Mississippi State University in 1981. It's very photosensitive, which means that the planting date doesn't make any difference with respect to the harvest date. It matures at about the same time."
"We started working with a company called ADVANTA, which is a seed company that is breeding and selling sorghum, and they're specifically working on energy sorghum, sweet sorghum for biomass and juice. They gave us three different day-neutral varieties, which means the length of the day does not affect the maturation of the crop."
For example, the M81E ripens in November regardless of whether it is planted in May or June. "When the days get short, it flowers and ripens," said Slack. "The day-neutral variety would mature purely according to the temperature."
"We bought a sugarcane harvester to do the harvesting," said Slack. "It's a pretty impressive machine. It cuts the tops off of the sorghum and blows all the leaves away, and cuts it into four – 12-inch billets." Billets are short, rod-like sections of the stalks of the plant being harvested.
"We also leased a small mill from the same sugarcane company in Louisiana," said Slack.
Sweet sorghum is easier to process into ethanol than corn or other grain crops. Ethanol is produced from grain crops in two essential steps: First, starch contained in the plants' stalks must be broken down into sugars. The sugars then are fermented into ethanol by yeast in a similar process to how beer is made. When juiced, sorghum stalks yield sugars instead of starch, thus eliminating the first step of the conversion process for grain crops.
The juice from the sorghum billets is sent to a nearby refinery to be converted into ethanol. "They're very happy with the juice that we send up because it ferments in about a third of the time that it takes to ferment their corn mash," said Slack. "It takes them 60 hours to ferment their corn, and it's taken less than 24 hours for them to ferment our sorghum juice."