According to the notes for the 1.8 update, farmer villagers will harvest ready crops and replant them. The farmer will hold the produce (wheat, carrots or potatoes) they harvest for up to 6 stacks then it will fall on the ground. Using this information I setup a farm with a hopper minecart running underneath the crops to pick up the items they drop.
I'm having trouble making them harvest crops, even after giving them 6 stacks of each type of crop they can harvest. Am I doing something wrong? Can I make this more efficient?
More info: I made a 4 9x9 field of crops with 2 farmer villagers in it and fenced off.