The tipping point of global oil production will be accompanied by a dire energy shock, and we will have to redefine the concept of farming.

On Friday and Saturday last week, a potentially historic meeting took place in the rather unpromising location of the CIA, otherwise known as the Cardiff International Arena. Britain's organic farming community gathered en masse for the annual meeting of the Soil Association, and their theme was peak oil and farming in the post-petroleum era. Organisers and peak-oil whistleblowers alike thought that perhaps this was the first time an organisation in a critically affected sector has held a conference on the theme of peak oil.

If the peak-oil proposition is correct, the tipping point of global oil production will happen - largely unexpectedly - in this decade or early in the next, accompanied by a dire energy shock. The people in the room will be in the front rank of those first affected. They can also be in the vanguard of those who can offer a proactive vision of what a survivable post-shock future could look like.

Discussion ranged across many potential impacts and implications. Let me choose just two: the number of farmers, and where they farm. So oil-dependent is modern industrial agriculture, and so relatively few are the people employed in it, that we will need to redefine the very concept of a farmer after the peak hits us. Today our typical farmer might tend 500 acres with tractors and other expensive bits of oil-addicted kit. But in the post-peak era - with the oil price sky high, and oil supplies fast-shrinking and therefore probably rationed - our farmers will need to be tending an area of maybe one-tenth the size, using more human labour and strategic use of a tractor powered by something other than petroleum, plus good old-fashioned draft animals. Many more people will need to be working the land if we are to feed ourselves. When the collapsing Soviet Union turned the oil taps off on Cuba, 15-25% of the population had to take to the fields in some form or other. (The good news is that they succeeded, to the extent that nobody starved.) Today in the UK, 1% of us farm. In 1900, before mass addiction to oil, fully 40% did.

We will need to be farming in the cities and towns as well as the countryside. The conference heard encouraging stories of urban farming in Cuba, and how surprising amounts of fruit and veg can be grown on astonishingly small areas of land in cities.

Who is planning for this kind of counter-intuitive impact? Not governments, for certain, and very few individuals and organisations. There are oases of foresight. In the US, the City of Oakland has a target of growing 30% of its own food within the city boundaries by 2020. In the British Isles, community-level responses are underway in Kinsale, Totnes and other towns. The list is not long. Most people and institutions are either unaware of the coming tsunami, or in denial.

However, as became clear over the two days of discussion, there is much that organic farmers are doing that moves us away from oil and other fossil fuels. And there are many ideas on offer for what more could be done. As the director of the Soil Association, Patrick Holden, put it: "What I have found is that the prospect of developing a strategic plan to do everything we can to equip ourselves for a post-fossil fuels age is, strangely, an inspirational proposition."

Let us hope it proves so to many people. Different it will surely be.

The Soil Association's website has podcasts of presentations including my own.