Robert Shiller predicts the next bubble -- farm land
http://www.project-syndicate.org/commentary/shiller76/Englishv
The problems with farm land as an investment are that it doesn't pay high income and you typically can't use as much leverage. However, appreciation can be very good as Shiller is suggesting.
My strategy is to buy agricultural land in the way of growth and development, so that in the future it's highest and best use changes to something more valuable. I can accept low income, as long as it pays for itself as it appreciates. If you can find the right parcels with seller financing, this can be a good way to go. Especially if you are in a growing area and have a long term horizon.