Dog Eat Mud - dirty dirt eater

So I have discovered that in addition to having a sweet tooth for my electronics, my dog also loves to eat mud. Why do dogs eat dirt? There are plenty of articles on the web with explanations of why dogs eat grass, but why do dogs eat dirt?

The ground is starting to thaw and today on our morning walk, our little shichon started chowing on some mud. Yes, our dog was eating mud. Not just sniffing, not tasting, full out eating mud.

I quickly realized that we had this problem before. I dont really have a problem with it, except that they get very dirty. They burrow their snouts into the ground and their faces get extremely muddy.

A quick check around the internet confirms that once again I am not the first one having this problem. Here is a response to a question of "Why does my dog eat dirt" on Healthy Pet:

Most cases of dogs eating dirt or grass are behavioral problems. It is usually nothing to be worried about

Since the zuchons come from seemingly "clean" breeds I didn't think we'd have this problem. Also, its not clear whether we should stop his dirt eating or just let it continue.

It looks like there are forums of folks chatting about this problem. Interestingly, looks like eating dirt is not the dirties of habits... there are a lot of dog poop eaters - YUCK. At least he is not eating his own poop.