To be a viable biofuel crop for Arizona, the plants need to do well in arid environments. That rules out corn, which requires a lot of water, as an option in most parts of the Southwest.

"There are hundreds of plants that you could use as biofuels," said Ray. "Oil seeds where you can use the oil almost directly for diesel, cellulosic plants where you can break down cell walls into ethanol, and plants like sorghum where you use the sugar to make ethanol."

"I'm a plant breeder geneticist, so what I do is improve or change the plants for whatever's needed," said Ray. "I work on three very different crops. One is lesquerella, which is an oil seed. Another is guayule, a rubber-producing plant that also makes these amazing resins, and these resins can be burned directly or used in all sorts of different ways as a fuel source. And then of course there's sweet sorghum."

Called the sugarcane of the desert, sweet sorghum is one of the most promising crops for biofuel.

"Sweet sorghum is a tall grass, and it grows to about 3-4 meters," said Riley. "It can grow in about 110-120 days, and it produces a substantial amount of ethanol. We think we can get 500-600 gallons of ethanol per acre – generally for corn you get about 300 gallons of ethanol per acre."

Sweet sorghum also is easier to process into fuel than corn.

Ethanol is produced from corn and other grain crops in basically two steps: First the starch is broken down into sugars, and then the sugars are fermented into ethanol by yeast, just as beer is fermented.

When juiced, crops such as sugarcane and sweet sorghum yield sugars instead of starch, thus eliminating the first steps of the process for corn-based ethanol.

"Even after you squeeze the stalks and get the juice out, there's a lot of biomass that's still available," said Riley. "That could be used as animal feed as a way to supplement what a grower would be able to get."

Don Slack, a professor in the department of agricultural and biosystems engineering, has studied the irrigation needs of sweet sorghum. "It's known as a drought-tolerant, salt-tolerant, tough crop," said Slack. "Sorghum would be a preferred crop in a hot, arid region."

Sweet sorghum needs little water, and since it's not intended for food it can be irrigated with treated wastewater, which provides many of the nutrients the crop needs.

It also has very low nitrogen requirements, according to a study by Mike Ottman, an agronomist in the plant sciences department.

Said Ottman: "You wouldn't think about it but nitrogen fertilizer is made using fossil fuels. In the case of corn, maybe one-third to half of the energy that goes into growing the crop is the energy required to make the fertilizer."

"Sweet sorghum's not part of the food chain, so if there's more sweet sorghum that's going toward producing biofuels it's not taking away corn that's used to feed animals or people," added Riley.

The researchers are trying to develop a way to plant and harvest effectively two crops in one year.

"You could effectively double the growth, double the amount of ethanol per year, just because our growing seasons are much longer than other parts of the country," said Riley. "It's really taking advantage of our location."