A forum post on TrossenRobotics.com
shows what's called a
an Autonomous Micro Planter (AMP),
a small, six-legged robot named Prospero, that's
capable of drilling seed holes and depositing seeds in them.
The forum post includes two YouTube videos and several photos.
The author of the post, David Dorhout, describes this
category of machine as the first of four steps, saying
The other three steps involve autonomous robots that tend the crops,
harvest them, and finally one robot that can plant, tend,
and harvest--autonomously transitioning from one phase to another.
Prospero was designed for a contest sponsored by
placed first in the Parallax MCU segment
(there were also TI and MicroChip MCU segments).
The forum post links to
a PDF which explains the project in detail,
including source code.