40d:Irrigation

Irrigation is the process of making rocky ground suitable for farming. This is usually done by flooding it with water. Inside caves, rock cavern floor tiles that are covered with water instantly become muddy tiles, which you can then build farm plots on. There are many possible methods for getting the farm area muddy.

Dryland farming: farming without irrigation

Some locations have layers of soil a few z-levels thick. It is not necessary to irrigate soil in order to grow crops on it; it is possible to build a farm plot directly on any soil tiles, although the dwarven crops such as plump helmets can only be grown in a subterranean plot. In lowland areas, a farm plot built on any tile marked Outside can be used to grow outdoor crops such as prickle berries.

Reservoir irrigation

Dwarf Fortress uses realistic water dynamics, including measures of water depth. A depth of 7 is full, depths of 1 will evaporate, leaving the stone wet and thus suitable for farming. Your goal in irrigation is to get a section of ground to be 1's.

The reservoir method involves building a small reservoir between two floodgates and a farming chamber at least 7 times as large as the reservoir. a reservoir of 10 tiles, for instance, can water a 7x10 chamber effectively. Water is let into the reservoir by lowering, then raising one floodgate. The other floodgate then releases the water into the farming chamber. It spreads around, then evaporates after becoming 1 deep.

Note that you can stack these over Z-levels by instead using hatches, or even bridges -- in their default state, bridges will block water from travelling between levels, and the large surface area you can get this way can make the water spread over your farm area much faster than by using floodgates.

It is also possible to achieve the same result with a natural pond using the same technique. Doing so is easier in the short term but it is not advised if you want to keep replenishing your reservoir for other uses, such as well(s), for natural ponds have a very finite amount of water available. On particular maps, natural ponds can replenish themselves at the beginning of each spring.

Oldschool irrigation

1. Dig from the farm plot to any source of water, but keep a single tile of wall between the newbuilt channel and the water. Also, dig a passage from the plot towards lower ground that'll serve as the water drain.
2. Build a door or floodgate, and three mechanisms.
3. Place the door in the channel. The idea is that it'll block the water from coming through when closed.
4. Build a lever and link it to the door or floodgate.
5. Pull the lever so the door opens. Send a miner to dig that last wall keeping the water from rushing in. Alternatively, have the miner dig a channel on the last wall from the Z-level above. The miner will dig out the wall without actually having to stand in the way of the water.
6. Ideally, here the miner will run like hell. The water is actually fairly slow.
7. Use the lever to close the channel once you feel you've got enough water to spread over the area.
8. Wait for water to drain out to at least 1/7 per tile. You can use channels, grates and hatches to speed up this process - all you actually need is for the water to have passed over the tile.
9. Make farm.
10. Harvest crops and produce food/other materials
11. Cook food if necessary
12. ???
13. Profit!

Pond irrigation

Dig a farm room, and dig a channel one Z-level above it, creating a hole down into the farm room. Create a zone on the hole, and make it a pond. Your dwarves will attempt to fill it with water carried in buckets. As they dump water in, it will muddy the farm room floor. After it has been sufficiently muddied, disable or remove the pond zone until you need to irrigate it again. Dwarves can build farm plots in 1 unit deep water.

NOTE: Even though it works, this is probably the slowest way to irrigate a room since dwarves only carry 1 unit of water per trip. Especially if you don't have a more than one or two idle dwarves and buckets, or if the water source is far away. It also probably wouldn't work very well on larger farm areas.

NOTE: This probably doesn't work if your farm room is directly under the surface, not for plump helmets anyway. It's best to have your farm room and the above pond-room both be dug in a cave.

Wave irrigation

Although seawater is unfit for carrying to your farm in a bucket, areas muddied by seawater seem to be farmable. My favorite method of achieving this is building a farm room under a beach and making a hole in its roof, closable with a hatch, to let waves in.