(From Big Organic chapter, p. 183)
The food industry burns nearly a fifth of all the petroleum consumed in the United States (about as much as automobiles do). Today it takes between seven and ten calories of fossil fuel energy to deliver one calorie of food energy to an American plate. And while it is true that organic farmers don’t spread fertilizers made from natural gas or spray pesticides made from petroleum, industrial organic farmers often wind up burning more diesel fuel than their conventional counterparts: in trucking bulky loads of compost across the countryside and weeding their fields, a particularly energy-intensive process involving extra irrigation (to germinate the weeds before planting) and extra cultivation. All told, growing food organically uses about a third less fossil fuel than growing it conventionally, according to David Pimentel, though that savings disappears if the compost is not produced on site or nearby.
Moral of the story: eat local foods! Another bonus–food that travels less distance will be fresher and tastier!