Commentaire sur Le Lévitique 25:16

תרבה מקנתו THOU SHALT INCREASE THE PRICE THEREOF — i. e. you may sell it at a high price

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.

כי מספר תבואות until the Jubilee year is what he is selling you, as opposed to the actual soil.