Ricardo’s theory of rent:
States that the rent of a piece of land has been the excess of the yield of that piece of and over that of the worst land in cultivation.
He regarded that land at the margin of cultivation yielded no rent, indeed if rent was charged the land would not be cultivated. Farmers would have to pay more for the use of more fertile land, and the excess yield over that of “no-rent” land would be its rent. Hence the net return to farmers on a unit of land of any given fertility would tend to be the same.
Ricardo regarded the rent of land as a surplus or economic rent.