Read this guide to find out how to build a semiautomatic farm. It's called semiautomatic because you must replant the seeds after they are harvested. This works for:
- Signs/Fences (multiple)
- Water Bucket (multiple)
- Whichever one of the above crops you wish to grow
Start making a row of tilled dirt. It must be less than 8 blocks long. Put a water trough next to it. Put fences above the water. You'll learn why later. At any rate, plant your crops.
When you're done with planting, put a Dispenser at one end of the farmland row. Put 1 Water Bucket in it and make a means of activation (placing a Redstone Block or a Redstone Torch works, although levers are best) behind it. Now You're ready to make the collection system.
How It Works
When the Dispenser is activated, it washes away the crops, but not the farmland. They will flow into the Hopper and into the chest. You can take the crops out and plant them again, then repeat!