The purpose of this study was to determine the effects of use of petroleum diesel (D100) and biodiesel (B100) fuel blends compared to pure diesel on the engine performances of a farm tractor with a tillage implement in field. The experiments were conducted on a tractor engine using a blend of biodiesel and petroleum diesel in the ratio of 20, 50, 80 and 100 % of biodiesel in the blends. The tractor performed with each blend doing standard tillage in field spots of 2500 m2 with three repetitions. The specific fuel consumption improved as percentage of biodiesel increased in the blend, obtaining a minimum of 0.0966 (L/kWh) for Biodiesel Alone B (100). While the energy efficiency in the usage of fuel by the tractor decreased as the percentage of biodiesel in the blend was increased, showing a maximum value of 104.9 % for a 20 % of Biodiesel in the blend, with respect to the Diesel fuel (D100), whose efficiency was considered being 100 % as a referential value.