The London Telegraph dutifully reported the results of a study by the Manchester Business School, comparing energy use in organic and conventional farming systems. In a life cycle assessment - farm to fork - it found that many organic crops use more energy.
The energy needed to grow organic tomatoes is 1.9 times that of conventional methods, the study found. Organic milk requires 80 per cent more land to produce than conventional milk and creates 20 per cent more carbon dioxide, it says.
One note of caution: this was a government commissioned study, not one published in a peer reviewed journal. One of the longest-running studies comparing conventional and organic ag methods was published in Science in 2002. This Swiss study compared organic and conventional farming systems over 22 years and it found that organic farming used dramatically less energy. Why? Because one-third of the energy in agriculture goes into the production of pesticides and fertilzers.
The Research Institute for Organic Agriculture (FiBL) found that while organic systems tend to use slightly more energy in tractors and fuel, they use dramatically less energy overall.
Since crop yields were considerably higher in the conventional systems, the difference in energy needed to produce a crop unit was only 19 percent lower in the organic systems. Per area unit this difference accounted for 30–50 percent. Most of the difference was due to external production factors.
Organic farming needs only slightly more energy for infrastructure and machinery as well as for fuel, whilst markedly lower energy input for the production of fertilizers and pesticides.
Here's a graph of energy use, with K2 referring to conventional systems and O2 to organic.
<img src="http://www.fibl.org/english/research/soil-sciences/dok/img/direct-indirect_energy.jpg" width="315" height="287"
That said, once shipping and distance is taken into account, the picture gets muddy quickly. Do heated hothouses and local transport use more energy than unheated greenhouses in the south where the food is shipped longer distances? There's no easy answer to these questions.
What the Manchester study appears to do is to look at the entire lifecyle, but even the executive summary is filled with qualifiers about the actual lack of studies on life cycle assessment. Secondly, it admits that the analysis does not take into account benefits of organic farming such as biodiversity.
The full study is here: