Washington Post: My farm is in the foothills of the Appalachian Mountains in southwestern Virginia. Like many others who have recently made the transition from tobacco to organic farming, we sell our produce through local and regional channels, including the farmers market in the nearby town of Abingdon, population 8,000. Of late, a number of commentators have disparaged local food economies, based on two claims: First, that shipping food long distances in fully loaded tractor-trailers is more …