here is how i would do it
I did that quickly just to show what i think would add effect
I didnt add any new color
I would just add some texture of like pile of stonified sand
I also tried 2 small plant on the left but considering the color and my skill at drawing plants
it didn't turn out that great.
also changed the shadow on the cactus i didn't see the meaning of those high brightness dot there
take it as you will... that's just my idea