salt a soil sterilant?

[way to grow]

I've been doing a lot of studying lately. When urea is used as a source of nitrogen aren't we just slowly killing the soil? Does the salt kill the bacteria/microbes in the soil? When I'm selling customers on my organic prgram I tell them it does. I use the example of spilling ice melt on your lawn and how it kills it. Is this information correct? Thanks for your input.