reflect a property income gained from the ownership of an asset, but are a real element of surplus value and consequently of the value product, insofar as those rents are a flow of earnings which must be paid out of the new value created by the current production of primary products on the land. Such rents are according to Marx, part of the total cost-structure of capitalist production, and a component of the value of agricultural output. Forms of differential ground rent Suppose for example that the ruling world market price for quality wheat is about US$350 per tonne f.o.b. Even if two investors have the exactly same amount of capital to invest in wheat production, the economics of producing wheat at that price are going to be quite different, depending on the actual yields (the productivity) of the land they use. The same amount of money invested in wheat production on area A yields a bigger crop of wheat and more profit than on area B, if A is more productive, fertile, better situated etc. than B. But not only that – given a known yield per hectare and a known price per ton of wheat, it may be either economic or uneconomic to produce wheat on particular soils. There exists a “hierarchy of soil types”, and if market demand and prices rise, more of the less productive (or marginal) land may be cultivated; if demand and prices fall, less of the marginal land may be cultivated. Differential rent I That situation is the basis of what Marx calls "Differential rent I". It means that the investor who places capital to produce wheat on the more productive lands reaps an extra-profit or rent for his capital, on that land. This rent, of course, varies according to the total supply and demand of wheat and the ruling market price for wheat. However, the income from wheat production will also depend not just on soil quality but on the number of hectares of each kind of soil being cultivated. Thus the supply of wheat and the wheat price, and consequently the rents obtained from their fluctuation, will also be influenced by e.g. whether the expansion of wheat production in response to growing demand occurs on better or worse soils. Differential Rent II In addition, the profitability and productivity of wheat production may also be influenced by the ‘’actual amount of capital