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: Digging a channel from the surface will mark the tile below Outside. This means that cave plants will not grow there.

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.

Tree Farm Irrigation

To create an underground tree farm, you need:

• A large growing room in which the plants will grow.
  • The large room can be any size. For this example, we will use a 24 by 24 size room.
• An adjacent smaller filling room that will be filled with exactly the right amount of water.
  • To calculate the size of this room, see below.
• A water supply line such as a tube leading to a water source. (Tree-Cap Note: This does not have to be the same water supply you discovered underground, as the little mushrooms will start to grow on any subterranean muddy ground once the spawn enter the air.)
• Lever-controlled doors or floodgates connecting the large room to the smaller one, and the smaller one to the water supply. Doors are preferred as you don't need to link them to levers to open them just so your miner can get out of the water shaft.

There are 576 (24 times 24) floor tiles in the large room. The small room must hold enough water to cover the large room, the small room, and the space occupied by the door in between with 1 unit of water. Each tile of the small room can hold 7 units of water, so:

small = (large + small + 1) / 7

or:

small = (large + 1) / 6

577 divided by 6 is 96 and 1/6; rounding up, this gives 97. This is the number of floor tiles in the smaller room: a 9 by 10 room with 7 extra tiles. Be aware, however, that if you make your "large" room too large, some of the water from the "small" room will evaporate before reaching the other end, and you will not have enough water to coat the floor. This behavior was observed in a room of 42x35 tiles.

Now, get digging. The water supply connects to the smaller filling room by a 1-tile hole where a door or floodgate will go. The filling room connects to the growing room the same way, and the growing room needs a door too. Remember to have the doors in place before breaching the water source and flooding the water supply line!

When you do breach the water source, immediately forbid the first door your miner runs through (see, this is why we use doors), which should be the door closest to the water source. Don't bother forbidding the other two. Link all three doors to three separate levers and test the system. Close the door between the filling chamber and main farm area and open the door that leads to the water source. When the filling chamber is full, close the door to the water source, close the door leading to the farm, and open the door between the farm and filling chamber. The water should spread out and coat the entire farm in a thin layer of water. Then simply wait for the plants to grow, and harvest them when the time comes.

For reference, to the right is a diagram which displays the tree farm described above. Walls are light gray, floors are dark gray, and doors are white.

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