[yNnOs]

The reasoning is that he's folding lots of hands to this bet, whether its 600 or 1K. Probably any 8, maybe not J9, but thats prob the worst hand he called your raise after limping. If he calls the turn, you still got money in the pot with what may very well be the best hand, and he'll check the river regardless if he has an ace or not; maybe even a T to induce you to bluff. Then you check behind of course.

However, by checking behind on the turn, you open up the possibility that he'll fire at the river with nothing. Better yet, fire big hoping you read it as a bluff. You'll be hard-pressed figuring out if he has a T or an ace and probably fold. By betting the turn, I think you get money in if you're ahead and a free showdown on the river regardless.