WASHINGTON, May 12 (Reuters) - A corn-like plant that can grow as high as an elephant's eye on some of Earth's driest farmland shows promise as a "smart" biofuel that won't cut into world food supplies, an agriculture expert said on Monday.

Sweet sorghum, used in the United States mostly as animal feed, offers a 10-foot (3 metre) stalk that can be turned into ethanol without damaging the food grain that grows at its top, Mark Winslow said in an interview.

Unlike corn-based ethanol, which uses one and a half times as much energy in its production as it offers as an end product, sweet sorghum produces eight units of fuel for every unit of fuel used to make it in developing countries, Winslow said.

Even in the United States, where mechanized production uses more fuel, sweet sorghum ethanol should still have four times the energy yield of corn-based ethanol, said Winslow of the International Crops Research Institute for the Semi-Arid Tropics.

Use of corn-based ethanol also pushes up demand for this crop on international markets, cutting the supply of food grain, and that would not happen with sweet sorghum, he said.

"Sorghum isn't traded internationally, it's grown and consumed locally in dry areas," Winslow said. "Since you're producing the grain on this plant, it's not a trade-off as it is with corn."

The institute is a nonprofit, non-political organization that does agricultural research focusing on "smart crops" and production systems aimed at helping poor dry-land farmers without hurting the environment.

TEAMING WITH TATA

The research institute has teamed up with the Tata conglomerate in India for a distillery that produces more than 10,000 gallons (40 kilolitres) of ethanol daily from locally grown sweet sorghum.

The farmers who grow it can still use the grain to feed themselves, turning it into traditional porridge and flatbread, and their livestock, while selling the fuel-producing sugary liquid contained in the stalks to the distillery.

The crop can survive without irrigation, but also tolerate flooding and even some salinity, Winslow said. Because it grows in arid areas, it does not threaten sensitive rainforest as palm oil biofuel does in Southeast Asia and sugarcane biofuel can in Brazil, Winslow said.

Like other biofuels, ethanol made from sweet sorghum does not produce the emissions of climate-warming carbon dioxide that fossil fuels do.

Because it grows in some of the poorest places on Earth in Asia and Africa, it has the potential to keep limited resources from these parts of the world at home, rather than sending them to oil-producing countries, Winslow said. Sweet sorghum differs from the so-called grain sorghum grown on some 100 million acres (43 million hectares) of agricultural land worldwide, the institute said in a statement. Sweet sorghum could be grown on about half of this land.

The United States, the world's largest sorghum producer, is organizing a conference this year on using sorghum as biofuel. Other countries exploring this possibility include Mexico, Kenya, Nigeria, Mali, Mozambique, Uganda, China, the Philippines, Indonesia and Brazil.