I don't like the sand either. I think that there is far too much of it. I think that it would be just as effective it it were implied here and there instead of making the shirt look like a two-tone el camino. No offense meant, as I like el caminos, but that was my first thought.
Sand is not working, it looks like he is sitting on someones unshaven face, but you already knew that. It's a good concept. As I said before use the halftones sparingly as sand around the blanket. Move the placement in the center of the shirt placing the sun right above the potato so you have a nice compact composition.
comments that have been said already:
needs tanning oil bottle
too much ink for sand effect
good halftones on potato