Just as U.S. farmers are starting to roll to their fields to harvest crops, our South American counterparts are rolling to the field too, only to plant crops — with winter wheat being the exception in both cases.

Interestingly, the economics of the two key countries, Brazil and Argentina, are quite different. Much of that has to do with the different paths of the respective currencies. Brazil’s real has risen 20 to 25 percent since the end of 2016. Meanwhile, the Argentine peso has drifted sideways to lower after it was...