Did the soil test reveal a problem or was it just the topic of conversation?  I have learned the hard way that wheat following Indian grass won't survive.  It took three years to get wheat to grow in a field that had been in native pasture for years.  I suspect that wheat won't work on land coming out of CRP until other crops have been established.

The wheat would germinate and establish itself and then just out of the blue when you thought it was doing well it would shut down as if you had burned it down with gramoxone.  I researched it a bit and it appears that this is known problem whether drought or not.

Soybeans take a yield hit after milo.  I have been led to believe that was because the milo did such a good job of mining the nutrients out of the soil.  That could also be enhanced due to drought, I suppose.  The same thing seems to hold true for some crops following sugar beets.  I think Johnson Grass has an alopathic effect on some crops too, soybeans in particular.  I have had trouble getting wheat to grow in fields that had a heavy infestation of JG.