Great work! I've been building armor in 1/35th to the max and HO railroad layouts right in the same room. I have 1/48th scale WW 2 Aircraft hanging from the ceiling as well, and in many ways the 3 all work into the same application of painting (all acrylic paints) and weathering.
I posted many threads on these forums as well as Model Railroader and included many tips on each "side" of the hobby, one thing I have learned over the many years is ground texturing is the same for all dioramas. I use the blocks of soft green florist foam, the kind that looks like bricks, there are many possibiltiies in the use of this product to complete dioramas the size of yours and up to RR diorama sections.
After cutting the blocks down to the right thickness in varying layers I glue it to the scenery base board with Elmers white glue. After the glue dries I start to coat the foam with acrylic base coats of earth tone paints, then while the paint is drying I use the tracks, wheels or other means to make the impressions in the mud or dirt wtih the same tracks or wheels on the vehicles that will be in the diorama. Much in the same way you show in your fine work. I have been doing this with the foam bricks now for about 20 years and the cost of the foam is much less than any other medium I have found. The main advantage of the foam bricks is the cost, only a few $$$ for three in a pack. Many people overlook the art/craft section of the local hobby store and miss out on the fantastic amounts of diorama material in bulk. All of this mixes with HO rr scenery and large scale military, it's all the same technique and crossing from one to the other ahs taught me a great deal.
Experimentation is the key. Try making streams with "Minwax" Glossy Polycrylic wood sealant. Mix thouroughly following the directions as if you were coating a piece of woodwork. Pour into a trough (stream bed) and let the sealant flow, you will have to dam one end of the trough until the fluid sets up. Keep adding layers about 1/4 inch at a time and you should start seeing the effects of the water -look. Once again it is all about experimenting with any non-hobby product. Home improvement and craft products are out there and one starts to see the benefits of using the bulk items. One quart can of Polycrylic would last the average modeler a lifetime for intermidiate water scenery jobs.
One day I will borrow my mother-in-law's digital camera as I am still a film photographer and post photos of some of the ideas I have mentioned on this and the Model RR forums. But as with all of us in these hobbies I like to be 100% with the scenes I would be refering to, so please be patient. I have had a strong influence in the arts from a father who made huge contributions to the photography world through his work at Eastman Kodak and my mother who used watercolors to create all sorts of scenery paintings. So I have ahead start in the arts and my canvas is in the form of military dioramas and trains.
I hope I have shed a little light on this subject and the fact that the diorama in this post is somewhat in the shade does in fact add to the realism. Keep up the great work.
johncpo