Small robots may kill the tractor and make farming efficient
Many crops would not need so many pesticides if they were grown in close proximity to the other plants they naturally occur with... in some cases this is because other plants attract predator insects that keep other insects at bay... humans could never farm this way because harvesters just chop everything down at once...But a robot capable of recognizing all the plants could tell... and could selectively harvest just what is needed.I suspect this is a  very difficult problem however just because of how varied individual plants can be... telling plants apart can be hard even for trained humans.