This works well in HO or N scale ...
Start with a piece of scrap corduroy fabric, cut to the desired size of your field. It should be an earth color, tan or brown (or else gold or green). Study a photo of the type of field you're trying to recreate; often the fabric will look right as is ... otherwise:
Paint some glue into the "crevices" of the corduroy and sprinkle on some dirt or earth ground cover; let dry and shake off the excess.
Paint glue on the remaining "tall" parts, and sprinkle on green or yellow fine ground foam. Let dry and shake off the excess. Glue the piece down and that's it!