The bright-green hulk of our John Deere combine harvester crept across the field of soybeans. It was late in the day, early October, the sun low. A cloud of hulls and chaff spewed from the back of the combine, then swirled up around us and blazed in the glow. Sealed in the dustless quiet of the cab, Rick Hammond steadied the wheel with one hand and punched coordinates into a touchscreen computer with the other. The reel of the harvester head spun steadily below us like the paddle wheel of a river steamer, standing up stalks so that the…