MODERN agriculture has become wholly unsustainable. That鈥檚 the unsettling conclusion of an exhaustive study of energy use on farms over the past seventy years.
The study found that in 1927, when horses pulled the ploughs, 60 per cent of the energy used in working the fields came from renewable sources. But by 1996, when tractors had long since replaced farm horses, only 9 per cent of the energy input came from renewable sources.
On the face of it, there鈥檚 little to choose between the fuel consumption of horses and tractors. The study, carried out by Torbj枚rn Rydberg and Jan Jans茅n of the Swedish University of Agricultural Sciences at Uppsala, found that a tractor tilling a field burns fuel containing about 67 per cent more energy than the hay a horse would have to eat to do the same job.
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Tractors make up for their higher fuel consumption by being able to work later in the autumn, when the water content of the soil is greater and goes deeper. Partly because of this technological edge, farmers produced 2.4 times more food per hectare in modern times than in the 1920s. But they did so using 13 times as much energy.
The researchers used a novel technique called 鈥渆mergy analysis鈥�, to study the total energy embodied in a particular process. Using a combination of economic statistics and energy flows they calculated the original solar energy embodied in all elements needed to plough the field. As well as the fuel needed by the tractor and the food needed by the horses this includes less obvious inputs such as the energy needed to make tractor spares or the horses鈥� bridles, and the heating needed to warm the driver鈥檚 home.
More conventional analyses often assume that the energy cost of factors such as human labour is zero, Rydberg points out. 鈥淲e are looking at a complex system,鈥� he says. 鈥淲e need this type of analysis if we are to stand on a solid foundation.鈥�
But simply consigning today鈥檚 tractors to the scrapyard and replacing them with horses is no good, says Rydberg in a paper to be published in the journal Ecological Engineering (vol 19, p 13). That will just increase the amount of solar energy that modern farming needs. A large amount of the solar energy farming uses up goes on supporting the lifestyles of today鈥檚 farm workers, and horses need far more attention than tractors.
Ultimately, most of the energy we use comes from the Sun, ryder points out. Plants store solar energy and so does the rest of the food chain. And the planet stores solar energy from plants in the form of fossil fuels.
鈥淗orse traction would require more solar energy if the horse driver were to have the same standard of living as our tractor driver,鈥� says Rydberg. 鈥淭his type of analysis is important for understanding the effects of policies.鈥�
But while fuel sources that get their energy direct from solar energy are renewable, fossils fuels are not. 鈥淭his is a very big issue,鈥� says Rydberg. 鈥淲e desperately need more sustainable agriculture.