Hi everyone!
Start from diorama base.
Technique to produce this sand base is quite simple, but need some practice
I must say first, that base which is pictured on photos isn’t real diorama base, but A3 size temporary base for working on scenes composition. Real base is around 0.90 x 0.75 m and will be finished on last stages of work.
Take foam plastic mat (we use 50 mm thick) and make necessary terrain shape using knife. Then apply thin layer of paper on surface of the mat using white glue ( we use copies of receipts from supermarket cash-register, because they have equal size and appropriate thickness).
This procedure reinforces base and help to minimize amount of glue and sand which is needed on later stages. See how base look after this procedure:

Let the’s base dry out at least 24 hours. Then apply next layer of white glue on paper using brush and start applying sand using fine mesh sieve with flat bottom. Thickness of sand layer must be around 3-4 mm. Due to contact with glue sand will change its color to darker one. In approximately 30 munites ( depends on room temperature, glue, etc.) sand will start drying out and changing color to natural.
At this moment top layers of sand is pretty dry, but bottom layers – still wet. It’s time to start applying the tire and tread marks on sand. You have around 30-35 minutes for this process ( again depend from some factors), after which the sand will become hard. We use just appropriate size toy cars to imitate tyre marks.
Let the base get dry another 24 hours, and that’s it. You have a base.
If you need some correction on completed base, you may apply some amount of white glue ( mixed with water) on problem areas by using hand sprayer and adding sand through sieve.
We prefer not to paint sand at all, instead of this - try to find sand of appropriate color to keep good visual imagination from mix colors of sand, vehicles and figures. That’s why, for this diorama we use pure XF-59 color for vehicles, although real formula for Operation Granby vehicles is XF59 x 4 + XF57 x 1 + XF19 х 1
As for desert plants we use corn female flowers aka corn silk:

Thanks,
Nick