From an energy perspective, agriculture has a double role: it is an energy user and an energy producer. All stages of the food chain require one form of energy or another, and renewable energies such as biomass, solar and wind, could make an important contribution to its sustainability and productivity, through technologies useful in irrigation, mechanization, processing, conservation, transport, etc. These possibilities and reviewed and the potential of agricultural products and residues as renewable bioenergy with social, environmental and economic benefits are stressed.
The world's oil reserves are estimated to be 1 trillion barrels. At the present rate of consumption it is estimated these reserves will be exhausted in 45 years. All recent international efforts assessing the environment, including the 1992 Earth Summit in Rio de Janeiro, the IPPC, the UNFCCC and the various sessions of the Commission for Sustainable Development - CSD, refer to the massive consumption of oil and other fossil fuels as an aggravating global environmental problems, such as acid rain and the 'green house' effect. The Kyoto Protocol recently adopted in the context of the Climate Change Convention calls for a decrease in CO2 emissions only possible if energy efficiency and renewable energy sources are promoted with determination.
The economic use and promotion of renewable energy sources is vital to ensure food security for future generations, as farmers in the future may increasingly be faced with the difficult task of the need to produce higher quantity and quality of food. In industrialized countries there is already a trend to move towards an agriculture with less fossil sources in terms of direct (electricity, fuels) and indirect (fertilizers, pesticides) energy inputs. In developing countries, where agriculture is still largely enrage-starved, the required increase in energy intensity will depend on the availability of energy resources and on the price and other policies related to their utilization. In all countries, renewable energies will undoubtedly play an increasing role in agriculture production. Moreover, agriculture could become a major energy producer. The conversion of large amounts of agricultural residues into energy, taking into account that a minimum quantity must be left on site to recycle nutrients, can contribute considerable to national energy balances. This is the case with sugar bagasse in places such as the islands of Reunion, Mauritius, Hawaii and Cuba and, more recently, Nicaragua. The potential of combined production of sugar and electricity to be fed to the grid is very significant. Purposely grown biomass for energy has also high potential, especially in the context of land set-aside, land rehabilitation, and reforestation programmes, always taking care that this form of energy production does not enter in competition for land for food production, which must take precedence.
Energy for and from agriculture is a topic which requires increasing attention from policy makers and scientists as a key element of national and global responses to the need for fossil fuel substitution, enhancing environmental awareness, achieving emission targets and, more importantly, eliminating poverty and hunger from the rural areas of many developing countries.