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Mechanization of agriculture drastically increases labour productivity in crop production, playing a major role in industrialization by freeing up workforce for industry and services. These historical processes are well studied, but there is much less knowledge on their environmental implications, particularly the carbon footprint.

In this work, we aimed to reconstruct the complete historical process of mechanization in Spanish agriculture at the national scale, estimating the carbon footprint of traction through a life cycle assessment approach. The assessment includes greenhouse gas emissions from working animals and feed production, and accounts for the historical changes in the energy efficiency of the industrial production of machinery and fuels.

The results reveal an increase in the carbon footprint of traction from 3.1 Pg CO(2)e yr(-1) in 1900 to 11-12 Pg CO(2)e yr(-1) in the 1970s and 1980s, decreasing to 7-8 Pg CO(2)e yr(-1) in 2010-2014. Area-based emissions ranged 185-242 kg CO(2)e ha(-1) yr(-1) in 1900-1933, when the practical totality of traction was animal, and 503-540 kg CO(2)e ha(-1) yr(-1) in the 21st century, when animal traction had almost completely disappeared. Product-based emissions were similar at the beginning and at the end of the study period, as the productivity growth offset the area-based emissions growth. The results show a large peak in emissions during the main decades of the mechanization process. Thus, the large savings observed in the last three decades start from a very high emission level. The carbon footprint of traction could be reduced by mimicking the logic of traditional organic systems but still benefiting from modern technological efficiency, through the self-production of the fuel. Our analysis, however, shows that a simple shift to biofuels may actually increase greenhouse gas emissions and consume a large share of the current agricultural output. Therefore, its combination with significant reductions in fuel and feed demand would be necessary to achieve its mitigation potential. (C) 2019 Elsevier Ltd. All rights reserved.