The Farmland Bubble

Yes, 4 percent appreciation a month equates to "bubble".

From Farm Policy:

Meanwhile, Elizabeth Williams and Marcia Zarley Taylor reported on Friday at DTN (link requires subscription) that, “Midwest farmland is appreciating so fast that even professional appraisers are humbled by the pace. A good-quality parcel of farmland sold for $11,500 per acre around Bloomington, Ill., earlier this month. That’s up $3,000 to $3,500 from a year earlier, said Charles Knudson, an appraiser with 1st Farm Credit Services.
“In September, Knudson appraised a central-Illinois property at $8,100 per acre for an interested buyer, but it sold at auction in February for $10,150 per acre. He’s now appraising farmland at 4-percent-per-month gains, a rate that landowners once savored on an annual basis.”

 And see Robert Shiller's discussion at Slate.