Instructions
Go to the Facebook website, and log in to your account. Click on the "Farm Town" application on the left side of the homepage to load the game.
Open two new web browser windows. Repeat the process of opening "Farm Town" in both windows, so that the game is open in three windows total.
Select the first window. Click on the connection button in the top-right corner of the game window. Click on the green tick to turn the farm offline. Repeat this process in the other two browser windows.
Select the first browser window again. Click on the plow button in the bottom-right corner of the screen. Plow an area of the field where you would like to have the stacked field.
Repeat this process by plowing the same area in the other two browser windows.
Go back to the first browser window. Click on the "Save Pending Changes" button in the top-right corner of the screen, and then close the window. Repeat this in the second browser window so that you now have only the third browser window open.
Click on the "Save Pending Changes" in the third browser window, and then click the "Play" button on the navigation bar at the top of the window. This will refresh the game. Once the game has refreshed, your farm will have an area with three stacked fields.