The energy inputs required to produce the crops included nitrogen fertiliser, herbicides, diesel and seed production.

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Water was also plentiful it takes 1, 000 tonnes of water to produce a tonne of grain and an ingenious process known as Haber-Bosch makes synthetic nitrogen fertiliser easily available to grain farmers.

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Haber nitrogen was not used as fertiliser in large quantities until the middle of the 20th century, and for a good reason.

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Imagine if GM could be used to create crops that produced higher yields, or were resistant to drought or could even fix their own nitrogen and produce their own fertiliser.

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This nitrogen also bears the isotopic fingerprint of nitrogen derived through the inorganic processes of fertiliser manufacture and fossil fuel burning, and not of the way microbes do it.

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Fossil fuel burning and fertiliser manufacture now take more nitrogen from the atmosphere than all of the planet's nitrogen-fixing microbes - and there are a lot of those bugs out there.

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All organic crop rotations contain three to four years of no ploughing because grass leys use the sun's energy to fix nitrogen for subsequent crops in place of oil-based artificial fertiliser.

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