What is the more symbolic meaning of sowing 'with salt', please?
The symbolic meaning of "sowing a city with salt", is that the city's destruction is final and the city would now be barren and would not be rebuilt. They don't actually throw tons of salt down on a city so that life will literally not grow.
We see this brought home in Deut 29:23 and Jer 17:6.
Jer 17:5 Thus saith the LORD; Cursed be the man that trusteth in man, and maketh flesh his arm, and whose heart departeth from the LORD.
Jer 17:6 For he shall be like the heath in the desert, and shall not see when good cometh; but shall inhabit the parched places in the wilderness, in a salt land and not inhabited.
Deu 29:23 And that the whole land thereof is brimstone, and salt, and burning, that it is not sown, nor beareth, nor any grass groweth therein, like the overthrow of Sodom, and Gomorrah, Admah, and Zeboim, which the LORD overthrew in his anger, and in his wrath:
In Jeremiah 17:6, we see several words that are very descriptive of what the Holy Spirit is trying to convey and these words are quite complimentary to the use of salt, here.
We have the following word associations from the Lord to emphasize what He is trying to tell us.
Heath - Same Hebrew word in Psalms 102:17, Isaiah 32:11, Habakkuk 3:9, the Hebrew is translated, "bare," "naked," "destitute"; but as the parallel in Jeremiah 17:8 is "tree," some plant must be meant of which this is the characteristic epithet (Jeremiah 48:6, Margin), "a naked tree."A blasted or withered tree. The "heath" was one of the plants, according to PLINY (13.21; 16.26), excluded from religious uses, because it has neither fruit nor seed, and is neither sown nor planted. On page 216 of the Ancient Hebrew Lexicon, Heath Tree a tree that is destitute, naked.
http://www.searchgodsword.org/com/jfb/view.cgi?book=jer&chapter=017
Salt - (Deuteronomy 29:23), barren ground.
Following words are pretty much self-explanatory, but coupled with salt in this context, reveal salt as not being something that is savoring but rather, where no life can and will grow.
Uninhabited -
Desert -
Parched -
Wilderness -
AtG, I found Mark 9:49 very interesting and also found this which you may find helpful. I did.
http://ntresources.com/blog/?p=53
777