Energy demand and greenhouse gases emissions in the life cycle of tractors

Energy supply and global warming are two of the main challenges of 21st century. To produce food to satisfy the increasing world population requires using more assets, more energy and emitting more greenhouse gases. Studies approaching embodied energy into and greenhouse gas emissions from agricultural machinery are rare. This study determined the energy demand and greenhouse gas emissions in the life cycle of tractors. Four tractors with distinct power levels were evaluated: 55 kW (T1); 90 kW (T2); 172 kW (T3) and 246 kW (T4). Life cycles considered were obtained from three different sources. Consumption of the direct inputs used in the assembly phase and of the input used in the maintenance phase were accounted. The results presented higher embodied energy and emissions in life cycle than are found in the literature. The following indicators were determined: T1, 122.7 MJ kg−1 and 5.7 kg [CO2eq.] kg−1; T2, 91.2 MJ kg−1 and 4.2 kg [CO2eq.] kg−1; T3, 85.2 MJ kg−1 and 3.8 kg [CO2eq.] kg−1; and T4, 71.9 MJ kg−1 and 3.3 kg [CO2eq.] kg−1. The hypothesis that more powerful tractors would require less energy and emit less greenhouse gas per functional unit (mass and power) was proved. Tractor (T4) has 313.2% more mass than (T1), but it required 70.6% less energy and 72.7% less GHG per unit mass, or 84.7% less energy and 87.7% less GHG per unit engine power than T1. For further use in modelling, equations were provided to determine energy demand and emission associated with either engine power or tractor mass.