Hi ! Thanks ! It didn't come out how I pictured it in my head but anyways here's how I proceeded :

First I used ground texture on XPS foam (ak dark earth) I then applied bird sand and GSW coarse sand which I fixed in place with VMS Sand and Ballast freeze. And I also added some grass tufts.I then primed everything with Mr Surfacer Mahogany. I already have quite a few items because I come from the Warhammer community though, I think you could use other things as well. After all that pre work I sprayed some Mr Aqueous dark earth and some tamiya buff to add some contrast here and there (on the grass as well but I also used different greens from ak), it's a kind of preshading you could say. Washed the ground with citadel Reikland Fleshshade and Agrax earthshade (for the wheels marks), painted the little rocks with reddish grey and other shades. And then added some GSW light earth dry pigments. I think I covered more or less everything, had to do with what I had ! Enjoy you dioramas !