LOL! This will open a can of worms!
Good maintenance practices says that you should lube a chain after a wet ride when you know water spray has gotten onto the chain. Also, I oil my chain when it sounds dry. Riding in some conditions will dry out the lube quicker than others.
I ride a canal path that has crushed binder, or crushed stone as it's base. When I ride there, I clean and lube the chain after these rides. I also have to clean the bike because the dust gets everywhere on the bike.
Another thing to consider is HOW MUCH Lube to put on the chain. For the most part we tell our customers to apply ONE Drop per roller/pin on the entire chain and then a quick wipe of a shop towel. We hold to that for most any chain on any bike.
Of course the next question that will come up is WHAT LUBE? I have my own ideas on that also.