לְפִ֣י ׀ רֹ֣ב הַשָּׁנִ֗ים תַּרְבֶּה֙ מִקְנָת֔וֹ וּלְפִי֙ מְעֹ֣ט הַשָּׁנִ֔ים תַּמְעִ֖יט מִקְנָת֑וֹ כִּ֚י מִסְפַּ֣ר תְּבוּאֹ֔ת ה֥וּא מֹכֵ֖ר לָֽךְ׃
Quanto mais forem os anos, tanto mais aumentarás o preço, e quanto menos forem os anos, tanto mais abaixarás o preço; porque é o número das colheitas que ele te vende.
Rashi on Leviticus
תרבה מקנתו THOU SHALT INCREASE THE PRICE THEREOF — i. e. you may sell it at a high price
Sforno on Leviticus
תרבה מקנתו, you will buy it at a higher price than would have been the case if you had only rented it. The reason why the seller is entitled to a proportionately better price is that over a period of years any investment the owner makes in building on such property will be worth his while, and will be amortized over many years, whereas a rental agreement does not permit the renter to make such changes.
Rashbam on Leviticus
כי מספר תבואות until the Jubilee year is what he is selling you, as opposed to the actual soil.