[quote=@Onarax]
Did you read the part in the link where it said it exorcises evil spirits? Pretty sure that's as explicit as it gets. 

Also yes sowing the fields was used, but based upon the original texts and the bible being full of double meanings it was also meant to be a full blown curse. 
[/quote]

You linked me to an entire novel for which I have no cultural context. "Evil Spirits" could mean any number of things. Ancient Christianity believed fevers were sent from the devil. It could easily be that salt has some sort of medicinal use in Korean culture but as I have no cultural context I couldn't say for sure. Evil spirits could also refer to things such as bad luck, or witch curses for which salt as a purifying agent would likely have been used. It was never used as a weapon against demonic forces or prevented them crossing the threshold of a house. That was a liberty taken on the part of Supernatural. Salt I will admit played a role in several ancient mythologies similar to how incense does in Christianity today. However it never had any offensive implications towards the demonic element.

And I still don't know anything about Spiderwick so using it as an example doesn't do me much good unless you want to explain exactly how it applied to the discussion.

You can't cite hypothetical double meanings which are completely up to interpretation as a source. You could argue the true meaning of the bible till doomsday and you still wouldn't have any proof of what you think it says.