Your probably correct to look at it from the Wheat Acres planted.. more specifically SRW Wheat. 

W1891 made a pretty good observation above..

http://talk.newagtalk.com/forums/thread-view.asp?tid=450914&mid=3655181#M3655181

I would guess soft red wheat planting ease and acreage plays as big or bigger role in fluctuating double crop acres rather than pure price change. Very poor SRW planting weather in fall 2009 led to low double crop beans acres in 2010. Thousands of failed corn acres in SRW country in fall 2012 went to wheat for harvest in 2013 hence large double crop area.  

Out here price makes a difference.  We geared up specifically to do double crop.. but as prices fall we will quit.


Nice graph. 

Thanks.