The farmville tractor allows you to plow 2x2 plots with one click. This saves you clicking. You can purchase the farmville tractor from the market once you have reached level 12. The farmville tractor will cost you 30,000 coins.
When you purchase the tractor from the farmville market, it will have a full fuel tank. The fuel that comes with the farmville tractor will plow 150 plots. After that, you will either have to purchase more fuel or wait 6 hours for your tan to refill. If you planted a crop that takes 6 or more hours to be ready to harvest you will not need to buy fuel.
To plow with your tractor, click the tractor and click Plow in the tools menu