But this is not true. The farmers who are quali-
tatively more efficient find greater opportunity for
the employment of their superior skill and knowl-
edge upon the more productive, than upon the
less productive land. The farmers who possess
a relatively high degree of qualitative efficiency
can win a larger return from land of any grade
than can their less efficient competitors, but this
extra product due to superior ability is greater
on the more productive than on the less productive
land and for this reason the more efficient farm-
ers compete only for the more productive land,
and are willing to pay more for it than the less
efficient farmers can afford to pay. The qualita-
tively less efficient farmers go on competing for
the less productive land until marginal farmers are
shifted to marginal land. Hence, the difference
between the rent of marginal land and that of the
more productive land cannot be measured in terms
of dififerences in the amount of the surplus which
would exist if land were the only factor which
varies in productivity.
This can be illustrated by means of a diagram.
