What does a tractor do in FarmVille?

A tractor is one of the tools you can purchase that will ease the help of your farming. A tractor specifically does plowing. When you us the plow tool, you can only plow one square at a time. However, when you have a tractor, you have the ability to plow up to four squares at one time. This saves you time, and the amount of clicks! The catch is though, it requires fuel to run.
When you purchase one of the pieces of farm equipment (Tractor, Harvester or Seeder) you automatically get one free bar full of gas. This bar is a meter showing you how much gas you have to run your vehicles. When it gets empty, you can purchase more to continue plowing or you can wait for it to refill if you rather save money.