This is the VOA Special English Economics Report.

What happens when a food crop becomes a fuel crop? This is a question many people are trying to answer as demand for ethanol increases. The issue is important not just to farmers and the energy industry.

President Bush began a Latin American trip in Brazil Thursday for talks with President Luiz Inacio Lula da Silva on subjects including biofuels. One goal is to increase production of ethanol from sugar cane in Central American and Caribbean nations.

Together, the United States and Brazil produce more than seventy percent of the world's ethanol. In the United States, ethanol is produced mostly from corn, or maize, and is also imported -- with a tariff that critics call protectionist. Brazilian ethanol production is mainly from sugar cane.

In Brazil, about forty percent of all motor fuel is ethanol, also known as ethyl alcohol. Many Brazilians drive flex-fuel vehicles. These can use either gasoline or ethanol. They are so successful, General Motors has stopped making cars for the Brazilian market that only use gasoline.

In the United States, vehicles that run on pure ethanol are rare. But most cars can run on a mixture of gasoline and ten percent ethanol. Some states require an ethanol-gas mixture to cut pollution.

Yet the use of an important food crop for fuel has led to concerns. Ethanol now makes up about twelve percent of all corn use in the United States. At current growth rates, that could nearly double by two thousand fifteen.

The American Midwest is known as the corn belt -- that is where most of the nation's corn is grown.

Some people worry that strong demand may push up food prices and reduce supplies of corn for food aid or farm animals.

Fuel researchers are exploring additional ways to make ethanol. One possibility is to use the remains of corn plants left in the field after harvest. This material is known as stover. But stover protects against soil loss to wind and water.

Researchers are also developing "cellulosic biomass" -- things like grass and tree bark, which are normally considered waste.

The Department of Energy says the United States could produce more than one billion tons of biomass a year. But the technologies to make ethanol from biomass do not exist yet. The government says developing these new technologies could take five to ten years.