plants. In Germany, sugar beet, wheat and rye are mainly used for this purpose. By adding biofuels to their blend, oil companies are complying with their ... cell tractors would be lighter and almost as fast to refuel as a diesel engine. However, both the technology and the fuel are currently still expensive ... problems in different kinds of tractor, as can vegetable oil fuel, once the engine has been modified. But these have thus far failed to make significant inroads