they can not be refuted.

They claim that the danger of an over-population in a not-distant future
lies in the law of a "decreasing yield of the soil." Our fields become
"tired of cultivation;" increasing crops are no longer to be looked for;
seeing that fields, fit for cultivation, become daily rarer, the danger
of a scarcity of food is imminent, if the population continue to
increase. We believe to have proved beyond doubt, in the passages on the
agricultural utilization of the soil, what enormous progress mankind can
make with respect to the acquisition of new masses of nutriment. But we
shall give further illustrations. A very able landlord of wide acres and
economist of acknowledged worth, a man, accordingly who excelled Malthus
in both respects, said as early as 1850--a time when chemical
agriculture was still in its swaddling clothes--on the subject of
agricultural production: "The productivity of raw products, especially
foodstuffs, will in future no longer lag behind the productivity of the
factory and of transportation.... Chemical agriculture has only started
in our days to open to agriculture prospects that will no doubt lead to
many false roads, but that in the end will place the production of
foodstuffs as fully in the power of society, as it lies now in its power
to furnish yards of cloth, if but the requisite supply of wool is at
hand."[233]

Justus v. Liebig, the founder of chemical agriculture, holds that "if
human labor and manure are available in sufficient quantity, the soil is
inexhaustible, and can yield uninterruptedly the richest harvests." The
"law of a decreasing yield of the soil" is a Malthusian notion, that had
its justification at a time when agriculture was in an undeveloped
state; the notion has long since been refuted by science and
experience. The law is rather this: "The yield of a soil stands in
direct ratio to the human labor expended (science and technique being
included), and to the proper fertilizers applied to it." If it was
possible for small-peasant France to more than quadruple the yield of
her soil during the last ninety years, without the population even
doubling, much better results are to be expected from a Socialist
society. Our Malthusians, furthermore, overlook the fact that, under our
existing conditions, not our soil merely is to be taken into account,
but the soil of the whole earth, that is, to a great extent, territories
whose fertility yields twenty, thirty and