I know, this is counterintuitive, but it actually works.
I came up with the design while writing Waffen, but it was one of the scenes I ended up cutting. Still, it was a good idea, so why not put it out free on the Internet (where all good ideas go to die in obscurity :)
First, the two biggest problems with growing anything in the desert is A. Water, and B. The dang heat! Using a greenhouse to solve both seems irrational on the face of it, but, believe it or not, it works. And it's unbelievable cheap too!
Materials list. A few hundred feet of plastic tubing or pipe (preferably the stuff used for radiant-heat floors), some sticks, a shovel, and two rolls of plastic sheeting, one clear (10'x200') and the other white (25'x200').
Yeah, that's more or less it! Told you it was cheap!
Start by digging a trench at least five feet down, three feet wide, and 200' East to West. Digging down allows geothermal to keep the plants cooler than they would be on the surface. Now grade it so that it will drain, preferably to one end, then line it with the white plastic. Dig two "pits" or holding tanks where the water will drain and line them with plastic.
Add topsoil back into the trench.
But wait, you say, you're in the middle of the desert! This might keep the water needed to grow plants from evaporating, but you still need an awful lot to begin with and you're still in the middle of a desert!
Ye of little faith : ) Let me continue.
Basically, the trench stays cool because it isn't all that wide and it's five feet or more below the surface. Five feet is kinda that magic zone where those geothermal air conditioners work.
All that dirt that was taken out of the trench is not going to go to waste. Run a pipe from the drain tank, slightly up grade, about five feet behind the trench along its full length.
This is the air intake. As hot air escapes the greenhouse, this will pull in fresh air. That hot air will be the long trip through the cooler dirt and the moisture will condense and be captured by the tank.
On the other side of the trench, another vent pipe travels the other way, through the same mound of dirt, and emerges at the surface. This is the exhaust vent. It too goes through the cool dirt and condenses the moisture that would otherwise have escaped the greenhouse. But unlike the intake, it's attached to a vertical piece of black pipe. The black pipe heats, the air rises, and it draws the air for you.
Eventually, even without bringing any water of your own, it'll pull enough moisture from the air to fill the tanks. But, of course, bringing your own would be faster.
Watering can be done manually at night, or first thing in the morning when the loss of moisture would be minimal for opening the greenhouse 'roof', but an automatic system isn't that difficult to rig.
A black bucket or length of pipe and some one-way valves can be used as the pump. The sun makes the air expand during the day, and the cool night makes it draw a vacuum during the night. The vacuum can be used to draw the water up into a gravity-fed soaker hose or sprinkler system.
A hand pump would also work just as well and would remove the need to open the roof and let the moisture out.
The 'greenhouse' can be shaded to regulate its temperature, if needed.
It can also be used to recapture the moisture out of the stalks and leaves as they dry and decompose inside it.
Yes, I know this design has downsides.
First, the rows have to be very narrow or else it loses its geothermal cooling. And the rows have to be spaced much further apart than conventional farming practices.
But irrigation this way is ultimately cheaper, and it would allow crops to grow in places that would be impossible otherwise.
Food for thought.
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