Eco-energetics analysis of an agricultural system: The French case in 1970

Abstract Eco-energetics analysis is used to describe structure and functioning of the French agricultural system. Data are for 1970. For the energy inputs, the most costly items are these related to motor driven equipment and chemical fertilizers. For motor driven equipment 153.7 MGJ (megagigajoule = 10 15 joules) are due to the use of carburants (energy directly used) and 53.8 MGJ to indirect energy. For fertilizers, 149.7 MGJ are used, principally for the production of nitrogenous fertilizers. These two items, motor driven equipment and fertilizers, represent a combined value of more than 60% of the total energy inputs: one is likely to find similar values for the agricultural system in most industrialised countries. Other items, such as construction, buildings and electricity are not negligible, 41.2 MGJ and 15.1 MGJ respectively. Concerning the outputs of plant products, the major part is for animal feed; this represents 1,441.2 MGJ to which is added 15 MGJ of imported plant products. For half of this animal consumption (720 MGJ), the source is crops with very high energy input, such as artificial grassland, fodder crops and cereals; the consumption of grain cereals (217.7 MGJ) represents half of the total production of these items. Furthermore, the cereals represent the only important export from the system at a value of 142.3 MGJ. For human consumption crop products supply a gain of 177.2 MGJ to which is added 43.7 MGJ of meat, 37 MGJ of milk and 2.5 MGJ of eggs. In the sub-system “husbandry”, energy consumption for rearing activities (70.7 MGJ) must be added to energy used for the production of animal consumed crop products (378.2 MGJ) and for animal feed processing (47.2 MGJ). Energy devoted to human food production is 180 MGJ. The total energy input is 596.5 MGJ, of which only 4.2 MGJ is man power and 8.4 MGJ animal power. For the products of human food, the French agricultural system needs 1.45 units of energy to produce one unit: it is a better value than for other modern agricultural systems. Efficiency of human work equals 94: this figure is logically part of all agricultural systems in industrialised countries. Sixty-eight per cent of the energy used comes from imports. Economies of energy must be realized and positive action could be done by different ways: avoid overequipping and quick obsolescence of materials; foster adoption of a more systematic use of rotations; use fertilizing possibilities from plants with nitrogen-fixating symbionts, from manure and other organic wastes; study carefully advantages of close rearing-crops relationships.