So here's the thing. Potatoes rock. Far, far better yields for acre than maize, rye, wheat or any other cereal, far less vulnerable to rampaging armies and antsy nomad raiders, and far more nutritious to boot.
And it's not like Ming and Qing China have been coy about adapting the sweet Potato or Maize (widely grown in Manchuria today) from the Spanish and Portugese. And yet, the Potato, ideal for the manchurian climate and heavily grown on the Russian side of the border, has never been widely used in China.
What gives? It would seem to give the enterprising Shandong settler leasing a plot of land from a Manchu/Mongol bannerman, not to mention his relative suffering from famine and warlords a serious leg up compared to his neighbors- and nada. How come the Potato never got established in Northern China?