An agricultural university organises a training event in which farmers from a particular village are invited to visit a nearby demonstration plot, where a new high-yielding variety of wheat has been grown side by side with the traditional local variety under identical management conditions, so that farmers can directly compare and evaluate the difference in yield, disease resistance and grain quality for themselves. Which extension teaching method, generally conducted over the crop's full growing season on a farmer's own field, is being used in this event?