Ibn Ezra on Numbers 18:19

ברית מלח. ברית כרותה מגזירת ארץ פרי למלחה ומקום המלח כמו נכרת שלא יעלה בו צמח כלל וכן גפרית ומלח: COVENANT OF SALT. A “cut covenant.”⁴²The Biblical term for making a covenant is, to cut a covenant. Hence I.E.’s note that a salt covenant is a variant of a cut covenant. The word melach (salt) is related to the word melechah (salt)⁴³In that both words have the meaning of cut. in A fruitful land turned into salt (Ps. 107:34). A salted place is said to be cut off, for nothing grows there. Compare, brimstone, and salt⁴⁴The verse reads: brimstone, and salt, and a burning, that it is not sown, nor beareth, nor any grass groweth. (Deut. 29:22).