We should all remember to take things with a grain of salt. This includes words from excellent classical sources. Even the Cambridge Ancient History.
In a meandering thread originally on academic Prose Style, from the Classics-L, that twisted once to challenge Augustine’s position on the rarity of silent reading, and turned again in a tangential direction, David Schaps brought up the proverbial sowing the fields of Carthage with salt to signify the permanent destruction of Rome’s old enemy.
He cited an article from 1986:
“To be Taken with a Pinch of Salt: The Destruction of Carthage,” by R. T. Ridley; Classical Philology, Vol. 81, No. 2 (Apr., 1986), pp. 140-146
that debunks the myth of the sowing of salt in Carthaginian furrows.
First Ridley looks through the ancient sources whose accounts of what happened to the conquered land at the end of the Third Punic War vary. Was it plundered, as with Appian? Destroyed utterly, as with Strabo [See Greek and Roman Historians] ? Cursed, as with Dio (from Zonaras’ epitome)? Consecrated, as with Cicero? Ploughed over, as with Niebuhr? Salted…?
He concludes that the story of salting the earth was based on Biblical and Near Eastern stories and first included in our stories of Republican Roman history, in the relevant 1930 Cambridge Ancient History entry by B. Hallward, who wrote:
Buildings and walls were razed to the ground; the plough passed over the site, and salt was sown in the furrows made.
Scullard, Picard, and other historians followed in his wake.
As Ridley alludes to, arguments from silence aren’t conclusive: there may be an ancient source who mentioned it, but his search was thorough and he couldn’t find it.