Just my observations:
1. The dirt looks like really slick mud to me. Not sure if that's what you're going for, but it looks wet, I think it's a combination of the dark colors and very light highlights with the smooth texture and deep pits in it.
2. I think you should make the transition more... grassy. As in actually shape it to the blades of grass that are at the edge of the transition. As it stands now, it looks to me like the grass just fades into the dirt, or ends in splotches, sort of like the grass is just painted on. You should retain the definition of the grass up to the very edge. Remember, these are actual individual blades, not just a texture.