Desert Diorama?

Use sand. I use fine playground/sandbox sand for desert dios. Simply spread some white glue (Elmer's School Glue) on your wooden base. Next, sprinkle the sand over top. Next add larger rocks and any vegitation you want. That is it. Not too difficult making a simple desert dio base.

You can use sandblasting sand.
Thats what I use I spend about $6.00 for a 50bl bag.
You can also use sand fom the of a river,just dry it.
One more thing crush some racks from your yard, that way you can have it as rough
or fine. And it feels good to SMASH somthing.
ARTE ET MARTE
djw1

That's ok, but wont be too pleasent to the eye, if u want a better strategy use the beach sand, playground sand, whatever, and mix it with white glue (elmers glue) in a bowl with water. After it has thickened spread the sand on the base and it might take a week to dry perfectly, depends on how much you use. Good Luck!
-ERAD

If the sand is too coarse, pour or shake it through a sieve or strainer or colander or even screen, you can get different sizes so you can decide wich one you want.

You could also use either sanded or non-sanded tile grout for a base, basically just add to your base, and a quick spray with some water, then add your whte glue/water mix to harden, and just as it's curing, you can add wheel ruts, foot prints etc...

Whether you use sand, playground sand or whatever, IMHO, you'd be better off applying a layer of Celluclay or plaster to the base before the sand. You could also mix the sand in. Unless you are doing a paved section, nothing in nature (except maybe the Utah Salt Flats) is as flat as a board.
Using this type material will also allow you to create slight depressions for tracks and give you a better way to blend any vegetation into the scene. With Celluclay (available from any decent hobby shop) you can mix in acrylic paint and sand to get the color and texture you want before you lay it down. Adding white glue (like Elmer's) will give you better adhession to the base.

Just to add to AJ's comments, by just putting down the sand/grout/whatever, you can still shape and mould your scenery as it's curing..ie wheelruts, etc.
I stopped using plaster as a base, as it got too heavy, now all of my non city dios are just striaight tile grout, and I mix in different sizes of rail ballast for rocks, then I will paint the surcace, add a wash, then finalize by drybrushing.
Of course, what you do in the end is entirely up to you!

My diorama is for a 1/72 stuka, will sand still be able to be used or will it be out of scale?

It will probably be a little too big and out of scale. You could try it on a small scrap piece of wood or whatever you want and see how it looks. Best bet is to find the finest sand you can and see how it looks.

Good luck.

Thanks for all the help guys!