I have made a 1x3x4 sugarcane farm. I don't know if its the smallest, or even the first time someone made this, but I made this myself.

Materials to build:
Water Bucket x 1
Sand x 1
Piston x 1
Observer x 1
Rail x 1
Sugarcane x 1
Block of Choice

Any YouTuber is allowed to make a video of this, as long as you link this post to it and link the video in the comments of this.

When Building: Make sure the powered rail is facing Forward/Backward