Soybeans and corn may become hot new fuel sources if high fuel prices and low crop prices continue. Bio-fuels, such as corn-based ethanol and soybean oil, burn more cleanly than gasoline and could help stabilize the faltering U.S. farm economy. Ethanol has been in production as a fuel additive since the 1970s, but President Bush may give it a boost — he is considering requiring California to use ethanol to help meet clean air goals, instead of the petroleum-based fuel additive MTBE, which has been found to pollute groundwater in the state. Meanwhile, testing of bio-diesel, usually 20 percent soybean oil mixed with 80 percent diesel, suggests it performs as well as diesel fuel and pollutes less. Last November, the U.S. Department of Agriculture began paying producers to increase use of bio-fuels, and at least five states are now considering tax incentives for bio-diesel use.