Agriculture and energies

Agriculture and energy: certainly a consumer, but also producer of unsuspected energy resources.

Biofuels, anaerobic digestion, wind electricity: agriculture is thinking about it every day a little more, as the price of a barrel increases. This is because some farming practices are particularly related to the oil economy. His resources would allow him to partially free himself.

5% of the energy consumed in France is by agriculture and 10% by the food industry. More than half of the fossil energy (oil, gas) used for agriculture, 53% very precisely, is used for fertilizer synthesis. The synthesis of a unit of nitrogen requires approximately one kilogram of oil equivalent. And the share of the cost of energy in the final price of fertilizer is 17%, it is less than 2% for a phytosanitary product. The average expenditure for sowing plowed land is 100 at 150 liters of fuel per hectare for corn and more than 100 for wheat. The drying of cereals is another big energy user: corn at 35% moisture demand 25 at 30 kg of propane per ton. Regarding the irrigation of corn, 0,15 l of fuel per m3 of water in winder system and corn 1 500 m3 / ha is 220 liters of fuel / ha and 0,08 l of fuel / m3 for a system of integral irrigation ...
Finally, the fuel bill for a corn monoculture plowed, fertilized with 220 nitrogen units, irrigated at 1500 m3 and harvested at 35% moisture blithely exceeds the 500 l of fuel / ha / year.. The current average yield of a hectare of maize is 80 quintals or 8 tons of biomass. These figures show how much the increase in the price of a barrel could jeopardize the agricultural economy.


Oil consumption by agriculture and productivity growth in percentage for the year 1990 taken as a reference to 100, according to Jean Laherrère, former head of geological and mining research at Total. Click on the image to enlarge.

The risks of an agricultural economy subservient to that of oil

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These figures would not matter as much if oil were an inexhaustible resource. The downside is that it will get expensive. Because demand will become greater than supply with emerging powers like China or India and because the costs of extraction and refining will increase by having to fetch oil from - 6000 m under the oceans or by having to refine the tar sands.
According to very serious specialists in the oil economy, like Jean Laherrère, we have reached the limits of capacity to increase oil production, even as demand is expected to increase. We would have reached what petroleum economists call Hubbert Peak.


Click on the image to enlarge

Yet agriculture has the means to anticipate the crisis and respond to soaring oil prices. Firstly, it produces a lot of unsuspected energy resources, which are not valued: slurry methane, biofuels, combustible straws.

Straws, an interesting resource.

Let's see in "oil equivalent" and equivalent energy efficiency, the energy value of some agricultural products. Knowing that one tonne oil equivalent (Tep) produces 41,86 GJ (Gigajoule), energy released when the fuel is burned. A Tep corresponds to 25,8 quintals of corn at 15% moisture. Wheat is a little less energetic, since it takes 27,2 quintals to match a TEP.
Corn straw is another unsuspected source of energy, as one tonne of straw produces 15,2 GJ, the equivalent of 360 kg oil equivalent. Technological thinking about the energy recovery of this corn straw is well advanced in the Canadian corn plains. Wheat straw could also be valued. The United Kingdom did not wait. At Ely, not far from Cambridge, a power station operates from 1999 with 200 000 tons of straw / year for a power of 271 GW / h, equivalent to the needs of 80 000 inhabitants. The autonomy of the factory is 76 hours with 2100 tons of storage capacity. www.eprl.co.uk). Just like corn straw, 3 tons of wheat straw equals a TEP. This raises the question of the organic matter of the land, pillar of their fertility, and straw is an important source. This could be offset by the use of intercultures, or stolen crops.

Read also:  The 2005 biofuel plan

Unsuspected agricultural energy resources.

Upgrading into biofuels is another point of interest to agriculture, as long as the biofuel production methods respect the land. However, not all crops capable of producing bioethanol are of the same interest if we consider the ratio (quantity of energy released by 1 liter of biofuel / quantity of energy required for the production of 1 liter of biofuel). Indeed, there is no energy interest in producing 1 liter of biofuel, if it is necessary to consume (in the form of petroleum or fossil resources) the equivalent of more than 1 liter of this fuel. The studies diverge, but we consider wheat bioethanol not interesting, this ratio being 1,1, it is 1.6 for bioethanol made from sugar beet and 1,9 for oilseed esters if the the co-products are used, in oil cake for rapeseed for example, a source of protein that can help replace soy. These calculations being carried out on the basis of a yield of 30 quintals of rapeseed capable of supplying 1 L of esters, one hectare of wheat capable of supplying 400 L of bioethanol and one hectare of beet 2 L giving bioethanol. The use of crude vegetable oil as fuel seems to be the most econological solution!

Cogeneration, methane and French disengagement

Other possible agricultural resources also reside in cogeneration from methanization units operating with slurry and all other plant sources in the fermenter. Studies commissioned by pig farmers in the Meuse region show that at the European electricity tariff paid to the producer at 0,11 € / kWh, a unit of 350 sows and fattening could make its installation profitable. But at the rate of 0,059 € / kW (only half of the European rate), the buy-back price offered by the main French operator, it becomes more difficult to make profitable… France does not respect European commitments, a situation all the more environmentally damaging than methane (CH4) has a 21 times greater impact than CO2 on the greenhouse effect. In other words, upgrading a kilogram of biogas by combustion has a "negative" effect (negative in terms of carbon footprint and therefore positive on
greenhouse effect) even if we produce CO2. For biogas, the installation consists of equipping the slurry pit with a cover to collect the gases, an agitator and a heating system to initiate fermentation and installing a second pit for the digestates. Many farmers are thinking about it.
Agriculture has the technologies to reduce its oil consumption: direct sowing, no tillage, which spends 3 at 4 times less fuel for planting, intermediate crops of nitrogen-producing legumes.

David Lefebvre


Fertilizer consumption and productivity gain in agriculture since 1960. This curve allows us to foresee the consequences induced by the scarcity of oil. Without oil, without fertilizer, agriculture can meet the food needs. It is therefore a question of separating agricultural techniques from petroleum.Click on the image to enlarge

More information :
- Agriculture and Biofuels
- HVB biofuels
- The 2005 biofuel plan
- Live without oil

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