Sowed it with salt - Expressing by this action his hatred, and his wish, that when utterly destroyed as a city, it might not even be a fruitful field. Salt is the emblem of barrenness (see the marginal references).
Related Commentaries of Judges 9:45
Judges 9:45
45 And Abimelech fought against the city all that day; and he took the city, and slew the people that was therein, and beat down the city, and sowed it with salt.