Parashas Behar · Aliyah 2 · Passuk 25:15
Chabad.org — English translation + Rashi
Torah Temimah cites Sifra (Torat Kohanim).
English: “According to the number of years of crops.” And not [years] of blasting; and the minimum of years is two.
Classical derasha (Sifra).
The sale price is calculated by the number of normal crop-years remaining until Yovel, not by years of blight; the minimum period is two years.