Commentary for Leviticus 26:35

כל ימי השמה — The word השמה expresses the idea of something being done (passive infinitive; here Hophal); and the מ has a Dagesh in place of doubling that letter in the root שמם.

כל ימי השמה תשבות, for the 70 years of exile in Babylonia are to compensate for the years the land should have lain fallow during the sh’mittah and Yovel years.

בשבתכם עליה, “when you used to dwell on it.” From the words אז תרצה, “then it will be appeased,” in verse 34, up until the words בשבתכם עליה here, you will find ten references to Shemittah, in one form or another. The message is that the 70 years of exile in Babylon represented ten shemittah cycles. Seeing that the entire Torah is a string of allusions to the past and the future there is nothing surprising in this.