Question about yard tracks

[foulrift]

Although my track is all ballasted and I am happy with the results,I do have a question. I have seen many pictures of rail yards both prototype and model and have noticed that in some cases the yard tracks are either in good shape or there is a lot of dirt between the rails covering the ties.Is this condition something that is up to the railroad? How many modelers do this with their yard tracks? The reason I am asking is this-my layout is a switching layout and I'm not sure how much of a plus it would be to the overall look.Also if I chose to do this effect to my two yard tracks and industrial spurs,is there something commercially available that I could use or should I use real dirt? Thanks for any help/suggestions.
Bob