Here I've compiled several programs used for farming wheat, carrots, potatoes, or other crops using ComputerCraft turtles!
The original program was the 16x4 farm. I designed this program to be user-friendly. The turtle used in all of these is equipped with a diamond hoe on the left side, and a wireless modem on the right. Simply copy-and-paste the code from the "farm" program into a program with the same title on your turtle, and you're good to go. Optionally, you may wish to include the "startup" file, located in the root directory of the repository.
Another feature of all of these farming programs is that they allow a rednet error screen. If the "refuel()" function is unsuccessful, it will broadcast on a rednet channel titled "fuelturtle," which can be received onto another rednet display, and optionally, projected onto a 2x2 monitor array. I personally carry a pocket computer set to that frequency so I always know when my turtle is hungry. As of now, the fuel is placed in inventory spot #1, and the seeds in inventory spot #3, this may be subject to change down the line.
Speaking of down the line, I designed these programs to be function-heavy, so I highly recommend you read the comments in the code if you would like to tweak it.
Enjoy! -LemonAppleCherry