A certain amount of energy (power) is required to produce a rice crop. Humans, animals, or machines that burn fossil fuels can supply that energy. Most farming systems use a combination of power sources.
Human
Animal
Machine
When tractors are used, less than 50 percent of the power produced by the engine is being used to do useful work. This inefficiency is due to mechanical and heat losses in the tractor engine and transmission, and traction losses between the tractor tire and the soil.