Cover crop for xeriscaped backyard

Hi, I'm pretty new to permaculture, I've read a lot but just bought a house and am getting to put it into practice for the first time. My backyard is completely xeriscaped and  I'm looking for advice on a cover crop mix for pretty much slightly soily sand.  
There is also a tree back there that gives the area some summer shade.
I've been looking at mustard and comfrey because of their huge root systems and mineral mining, but what does well in sand for nitrogen fixation? Succession-cover cropping would be fine, I don't plan on turning the area into my perennial bed until planting time 2018.
Can anyone give me some advice on techniques and plants that would help me?  Thanks

Are you looking for something that will grow rapidly during the wet season and then leave roots in the sand when it bakes in the dry season?
Vetch can produce a fine green biomass that can easily be cut off at the soil level and used for the green/nitrogen part of your compost. If it has enough time to go to seed it can reseed In my field some comes back from the roots and a lot come back from seed.  We of course have a much longer wet season but from the 4 of July until the middle of september we get very little rain.  I cut some before it seeds and use it green and where the soil is poor I let it goes to seed and after the pods twist and scatter the seed I cut it dry for mulch.

Comfrey is good drought tolerance once it gets it gets a tap root deep enough.  It has to be planed for a permanent location because you will never be able to get the deep roots out and it will come again covering a larger area each time.

Can you harvest rocks? Acover crop of rocks on top of a hugle bed might work for a xeriscaped backyard.

We don't necessarily have much of a"wet" season here.  We have a less dry season. I'm looking for something I can plant and just let it have the area until next March/April.

If I need a succession of cover crops that would be fine. My plan is to chop and drop and let the roots add biomass.

I'm just not sure what cover crops do well in light shade and sand.  

You could try something that doesn't need nitrogen fixation, something that is well adapted to the soil and climate of Albuquerque, like Indian ricegrass.  It is possible to buy the seed in New Mexico, so you wouldn't have to go collect it.  With a little help (plant it, help it germinate with a little water, give it a little compost at crucial stages), you could raise a good stand of it as the first crop in your succession.  Or, since it is a perennial, use it as a backdrop to your whole permaculture.

There aren't a whole lot of possibilities given your climate.  Rather than try a cover crop mix adapted to wetter climates, go with what is adapted locally.

John,
So you're saying use Indian rice grass to build up the soil? At least until it has enough organic matter to grow other things?

Jerry Walton wrote:John,
So you're saying use Indian rice grass to build up the soil? At least until it has enough organic matter to grow other things?

Yes.  If you have wandered out on the west mesa near the petroglyphs, you may encounter stands of it in the wild.  Usually it doesn't build much soil and you just see scattered clumps.  That's because (1) lots of critters like the seeds, so it has a hard time reproducing, and (2) each clump that does get established has to endure the weather unaided.  If you have a block wall around it, that takes care of a lot of #1, and if you give it a modest amount of help, you can help it through a lot of #2.  With that help, it might turn out to be a good soil builder.

The common desert groundcover in the SoCal desert is a fine-leaf sheep fescue (which is a nutrient fixer) mixed with pineapple weed. The soil there is extemely alkali and entirely devoid of nitrogen, and rainfall can be as little as 1-2 inches per year.

https://en.wikipedia.org/wiki/Festuca_ovina
https://en.wikipedia.org/wiki/Matricaria_discoidea

This mix looks great and while it likes being grazed, it doesn't require mowing. Sheep fescue only gets a few inches tall. Pineapple weed can get big with lots of water, but under dry conditions stays around 4 inches.

Have you tried High Country Gardens? They specialize in drought tolerant and plants suitable for xeriscaping. Their plants are high priced, but the quality is good. Go to the sale pages first. I get their newsletter so I know when things go on sale. They'll ship when it's optimum time for planting.
They have several clovers, but they also have decorative grouncovers that bloom. Worth a look.

Hey Jerry,  I live in Tucson and found some good resources for dryland cover crops while researching for a design I was doing for a friend. Some came from the University of Arizona extension program, so you may want to check with your local college Ag extension too for locally adapted plants. But here's some of what I found:  

http://articles.extension.org/pages/31141/cover-crops-for-arid-areas   Cover Crops


https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1519.pdf    Cover Crops for use in desert veg growing systems.


http://cropsfordrylands.com/wp-content/uploads/Unconventional-Legumes-for-Sustainable-Farming-Systems.pdf    Unconventional  Legumes


http://cropsfordrylands.com/free-pdfs/          Alternative crops for drylands  


http://www.americanmeadows.com/wildflower-seeds/southwest#ideal_region=southwest&life_span_indi=perennials&mix_species=mixtures&sun_shade=full-sun&zones=9&gan_data=true  Wildflower mixes for the Southwest


http://www.desertseedstore.com/category/Native-Grasses-68   Desert Seed Store - Grasses


http://wc.pima.edu/~bfiero/tucsonecology/plants/trees.htm   Desert trees, mostly legumes. Good for shade, N2 fixing, wind breaks, and to act as nuclei for "fertility islands" and nurse trees for smaller plants under their canopies.


http://www.aridzonetrees.com/varieties.html    Arid zone trees, mostly landscape trees, but plenty of nitrogen fixers.


I hope this helps, I spent a lot of time researching these sources and have more if you want, just let me know.

Cheers, Joe

One thing to be aware of is that subterranean clover, which is a popular suggestion for dryland nitrogen fixing, has seeds that are dangerous to quail and other native birds. It has enough phyto-hormones that it prevents reproduction. I would suggest native clovers and grasses instead, or cowpeas, which are heat-adapted and attract lots of pollinators in a addition to fixing nitrogen.

Thanks everybody for the suggestions.