The Plow tool is used for plowing land. It can be used to make ready plots that have just had a crop harvested, so that new crop can be planted. It can also be used to create new crop plots for farming on. The plow tool will plow one plot at a time and take a few seconds per plot to plow if the farmer is not trapped.
From time to time, a farmer will find a coin worth 100 coins springing up from the field while plowing. Instead of 100 coins, only 25 coins will be added to the account immediately. It looks like this feature has been disabled as of July 3, 2010.
There is also a chance that while plowing the farmer may "strike oil - black gold!", and be given a chance to share some extra fuel with neighbors.