JWR,
Here’s a link to the September 2008 National Geographic cover story about the world’s fragile soils and their diminishing capacity to feed 6.5 billion+ people as well as cautionary examples of places where the soils can no longer support the existing population due to poor stewardship in the past.
Pages 92-93 of the hardcopy edition have a great fold out map showing soil fertility areas around the world — a good retreats and relocation general shopping reference (although certainly not detailed enough for researching specific properties). My Best, – Lee in Hurricane Alley