Capital, Volume Three: The Process of Capitalist Production as a Whole by Karl Marx

Thus far we have considered differential rent only as the result of varying productivity of equal amounts of capital invested in equal areas of land of different fertility, so that differential rent was determined by the difference between the yield from the capital invested in the worst, rentless soil and that from the capital invested in superior soil. We had side by side capitals invested in different plots of land, so that every new investment of capital signified a more extensive cultivation of the soil, an expansion of cultivated area. In the last analysis, however, differential rent was by its nature merely the result of the different productivity of equal capitals invested in land. But can it make any difference if capitals of different productivity are invested successively in the same plot of land or side by side in different plots of land, provided the results are the same?

To begin with, there is no denying that, in so far as the formation of surplus-profit is concerned, it is immaterial whether £3 in production price per acre of A yield 1 qr, so that £3 is the price of production and the regulating market-price of 1 qr, while £3 in production price per acre of B yield 2 qrs, and thereby £3 of surplus-profit, similarly, £3 in production price per acre of C yield 3 qrs and £6 of surplus-profit, and, finally, £3 in production price per acre of D yield 4 qrs and £9 of surplus-profit; or whether the same result is achieved by applying these £12 in production price, or £10 of capital, with the same success in the same sequence upon one and the same acre. It is in both cases a capital of £10, whose value portions of £2 1/2 each are successively invested – whether in four acres of varying fertility side by side, or successively in one and the same acre of land – and because of their varying outputs, one portion yields no surplus-profit, whereas the other portions yield surplus-profit proportionate to their difference in yield with respect to rentless investment.