I play Minecraft PE on my iPad, and PE doesn't have pistons. So I was wondering if there was any way to create an automatically irrigating farm(using iron doors, maybe?)
In my world I've built two different farms. The square farm and the sloped farm. Both of these are semi-automatic, that is you'll have to plant them manually, but they gather up the produce using water. Both farm types has loads of videos example available, but I've tried to explain them textually here.
The main idea is that one single water block placed in the center can irrigate an entirely 9x9 area. So I fenced in an area of 11x11, left one grass block inside the fence to collect the produce, and replaced the center block with a water block, and a block of your choice on top of it.
Then I hoed the area, planted some seed and waited for it to grow. When it came to harvesting, I sneaked into the center jumped on top of the block and put down a water bucket. This harvest everything getting it ready for the next round.
The sloped farm
The sloped farm is also a common variant of wheat farm, and it uses some of the same principles, but it can be extended to even larger fields (which does take some time to plant).
The idea here is to have long rows of harvest, interleaved with rows of water for irrigation. The same rule as above still applies, that a water block can be used to irrigate rows up until 4 away.
One layout of this in beautiful ascii art:
222222222211111111 ssssssssssssssssss s stonewall sWDfffffffFFFFFFFH W Water sWDfffffffFFFFFFFH D Dirt sWDfffffffFFFFFFFH f Farmland sWDfffffffFFFFFFFH F Farmland sWDhbhbhbhbhbhbhhH h halfslab on water sWDfffffffFFFFFFFH b block on water sWDfffffffFFFFFFFH H Halfblock sWDfffffffFFFFFFFH sWDfffffffFFFFFFFH 2 Level of all blocks in column ssssssssssssssssss 1 Level of all blocks in column
This scheme can be extended both column-wise and row-wise, if you are so inclined. Replace the last row with the last four rows, and/or the last column with the last 8 rows at a lower level.
I tend to use the water row for traversing the field to avoid stamping on the farmland, and for seeding. When the times comes to harvest, I temporarily remove the dirt allowing the water to flow down (i.e. from left to right) collecting all the produce and seeds on the last column of half slabs. Give the water a few seconds before replacing the dirt to stop the water flow.
Automating the water flow
One common variant of the sloped farm is to use pistons to raise/lower the dirt block I've suggested for holding the water. This is as indicated not available in MCPE ver 0.14, but I've been contemplating whether the water/dirt column can be replaced with a column of redstone dispensers (with a water bucket inside) hooked to a lever.
There are two vital notes related to farming, and the first is that you need to be somewhat close to the farm for it to grow. The exact distances I'm not quite sure of, and have heard different numbers. But I once tried growing sugar canes around 40 blocks away from my home (as there was sand and water), and they didn't grow. After moving that field next to my main house, they grow like crazy.
The second note is that if you add sufficient light it will keep on growing through the night (unless you are sleeping). And the lights also has the added benefit of keeping most of the mobs away.
So in my current setup I have made a sloped wheat farm on top of my house which was built in a hill. North of it I've made a moot to keep mobs floating away, and then five rows of sugar canes, and then north of that a square farm for ransom produce. (On the south side I've made a fenced area for cows and one for sheep.)
There is some videos out there on how to make these. For instance the Youtuber NebsGaming created an efficient one. This might just be what you had in mind.
Minecraft Pocket Edition - Automatic Farm!