Agriculture (2) Authors (2) Escritores (2) Agricultura (2) Agriculture (2) Écrivains (2) Agriculture (2) agriculture (2) Development (1) Construction (1) Employment (1) Costs (1) Methods (1) Tractors (1) Traction-engines (1) Petroleum (1) Oil fields (1) Machinery (1) Informers (1) Force and energy (1) Civilization, Modern (1) Building sites (1) Biomass energy (1) Agricultural machinery (1) Methods (1) Use (1) Usage (1) Procurement (1) Occupations (1) Effectiveness (1)