Sweet Sorghum: From Fields to Fuel

Professor Slack uses a refractometer to measure the sugar content of the juice extracted from the sweet sorghum.
November 21, 2011

How will we fuel the future? As a leading public research university, the University of Arizona is working hard to answer this question through pioneering research in alternative fuels. Here in the Sonoran Desert, researchers in the College of Agriculture and Life Sciences are looking into bio-fuel crops that can be grown in arid areas.

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“Sweet Sorghum in some ways is similar to corn,” says Don Slack, Ph.D., professor in the Department of Agricultural and Biosystems Engineering. “But it’s a much more drought tolerant, heat tolerant plant.”

Through the research in Slack’s lab, he and his graduate students are finding better ways to grow the plants and optimize their production of juice, which is then fermented into ethanol.

“This project is a pilot project,” he says, “which means that we move it beyond the laboratory into the field.” They are looking at how their methods scale to the field to see if they represent viable ways of growing bio-fuel and bio-energy crops in the bright, dry environment of Southern Arizona.

The UA has multiple agricultural research facilities; Slack and his team are working on their sweet sorghum project at the Red Rock Agricultural Center, a 320-acre facility 40 miles north of Tucson.

Broad-reaching Research

As a land grant university, the UA has a mission to serve the state, the country and the world.

“The land grant university has three very specific, important missions: education, research and extension. This project integrates all three of those missions,” says Slack.

Considering the energy challenges we face in the United States, the research Slack and his team are doing is of interest to a great many people and organizations, from private industry all the way up to the federal government.

“The Department of Energy is very interested in alternative energy – in particular, biofuels,” says Slack. “Arizona is one of the places where we can grow sweet sorghum very efficiently, so the Department of Energy has funded this research for the past two years.”

Slack is also partnering with Pinal Energy of Maricopa Arizona, a 50-million-gallon-a-year ethanol plant. Pinal Energy currently imports corn from the Midwest, so they are quite interested in the potential for locally produced sweet sorghum.

As a result of the efforts of Congressman Raul Grijalva, the United States Department of Energy is also helping to fund the project.

Crossing Disciplines

The project is a collaboration between the College of Agriculture and Life Sciences and the College of Engineering.

“We need to have plant scientists to understand how the plants grow and mature,” says Slack. “We need to have chemical engineers who understand how the materials can be refined into a product, and we need agricultural engineers who can work with machinery to extract the juices and process the materials.”

Such a combination of talents and areas of expertise is absolutely essential for the success of an effort of this scope and complexity.

Research Arising from Education

Slack has two graduate students working on the project. Tania Martinez-Cruz, a graduate student from Mexico, is looking at different varieties of sweet sorghum and how they grow.

Ilse Rojas, a Ph.D. student from Chile, is doing her dissertation research on how to get more return from the plant. Normally, the fibrous parts of the plant are discarded after juicing. Rojas’s work is focusing on converting that material, called bagasse, into sugars that can then be fermented into ethanol.

“As a scientist, I am focusing on some very important problems to our world like food security, water security and also energy security,” says Martinez. “Sweet sorghum is supposed to be a drought-tolerant crop. We want to know if we can use some lands that are not suitable for food production, using less water, but also guaranteeing some kind of energy for people here.”

It is harnessing that curiosity and passion in his students that Slack sees as the core of his work. In his eyes, offering a great educational experience is what gives rise to excellent research an innovation.

“We’re here to educate students, and the byproduct of our educating students is the research,” he says. “I love working with graduate students. It’s a favorite part of what I do.”