A barrel of oil: a ton of maize

According to FAO, 6,000 MJ of fossil energy (corresponding to a barrel of oil) is used to product one ton of maize in industrial farming, while for the production of maize with traditional methods in Mexico only 180 MJ (corresponding to 4.8 liter oil) is used. This calculation claims to include energy for synthetic fertilizers, irrigation and machinery, but not shadow energy, i.e. energy used for making machinery, transporting products to and fro the farm, and for construction of farm buildings (FAO 2000). The energy ratio is negative (below 1) for modern rice farming and just above one for modern maize farming, while traditional production of rice and maize give a return of 60 to 70 times on energy used . FAO has also compiled average data for energy yields for developed and developing countries respectively (see table). It shows that developed countries use more than double the amount of energy to produce a ton of grain, and three times as much per hectare (the reason for it being more per hectare is that yields are a bit higher in developed countries). FAO notes that “productivity is higher” when more energy is used, and with that they mean in particular productivity per labor unit. One could of course put it the other way round and say that the productivity measured on used energy is very low. When we discuss bio-energy this discussion is suddenly very relevant.

Different kinds of agriculture production and different food also have different energy ratios. The energy ratio is very low for deep sea fishing; for meat production from feed lots and from vegetables in heated green houses . A big share (often above 50%) of the energy use in farming is for the production of synthetic fertilizers, in particular nitrogen fertilizers, and pesticides. This also means that the contentious debate about organic vs conventional (non-organic) farming has a strong element of energy dependency debate. If improved energy ratio is a primary goal for farming, skipping, or at least dramatically reducing, nitrogen fertilizers is one of the best ways to get there.