For the base level soil I used Citadel technical paints. Citadel overcharges for everything, but I have to say that for their technical paints (this one was Stirland Battlemire, I think) the convenience was totally worth it and the applicator tool is indispensable. If I wasn't applying so much grass I would have drybrushed the finished product with a lighter brown or a grey.
I used Army Painter tufts which are super convenient and easy to apply. The grass is also Army Painter, though I didn't have a grass applicator. I just waited until everything was completely dry then spread PVA glue and turned the models upside down, tapping away the excess which also had the benefit of making the grass stand up. With a pair of small tweezers, I made sure to pick away all the excess grass then let it dry.