Grist: Some basic economic forces are driving mid-sized farms out of existence. First, food prices keep falling. "Ever since World War II, agricultural commodities have trended steadily down," agricultural economist Otto Doering told me. We are on a technology treadmill: Farmers get a new tech (like hybrid seeds), increase productivity, and make money. But then all the farmers get it, they all produce more, and prices drop, Doering said. Those new technologies cost money, so farm costs go up while food...