Joel,

Maybe my memory is wrong, but I was thinking that idea of alternating strips of crops was being kicked around 20 - maybe even 30 - years. 

suggestion:  maybe someone can help you identify exactly which model of JD tractor that is, and which model of cultivator that is.  IF you can identify which models they are, I would make a presumption they should be "fairly new", and use that to identify about which time frame that picture was taken.

Maybe a post in MachineryTalk could get you more help with identifying tractor and cultivator models. (Maybe you have already posted in MachineryTalk - I didn't look.)

P.S.  I would guess that is a "40-series" JD tractor - i.e. a 4640 or a 4440; however, it might be a 30-series also - 4630 or 4430.