soon
restore such soil to high fertility. In these conditions of exhaustion
the loss to fertility by soil leaching is small, because of the
non-soluble character of the earth particles. Thus experiments at
Cornell have shown that in the average foot of top soil from rather
unproductive farms in a low state of production, there was plant food
sufficient for 6,000 crops of corn. We have all seen a single thunder
shower remove from a hillside corn field the fertility adequate for the
making of a hundred crops of corn.

American agriculture is peculiarly soil destructive. Three of our
greatest money crops--corn, cotton and tobacco--require that the earth
shall, throughout the summer, be loose and even furrowed with the
cultivator, which prepares the ground for washing away, and by its
furrow starts the gully. The second factor in this peculiarly
destructive agriculture is the fact of our emphasis of rainfall in
summer. Third in the list of factors of destruction is the rainfall
unit, the thunder shower, which dumps water, hundreds of tons per hour
on every hillside acre. A little examination of the facts and careful
inclusion of the time element will show that the old-world saying,
"After man the desert" is quite as true in the United States as in
Europe and Asia, where it has been so fearfully proven in the seats of
ancient empire.

This soil resource destruction from erosion leads to the destruction of
other valuable resources. We appear to be upon the eve of an epoch of
waterway construction and experiment. The greatest injury to waterways
is channel filling by down-washed mud. Pittsburgh has been praised
highly for the energetic action of her Chamber of Commerce and citizens
in appropriating money for the careful survey of drainage basins above
the river, with the idea of obtaining knowledge preparatory to the
building of reservoirs to check floods. They have forty-three reservoir
sites, and the early construction of nineteen of these reservoirs is
recommended.

A part of the reservoir plan, however, is that the land above it shall
not be cultivated; otherwise the erosion from the tilled fields will
promptly fill up the reservoirs, as the present condition of many
eastern mill dams so emphatically attests. The carrying out, therefore,
of the Pittsburgh reservoir plan necessitates the exodus of hundreds of
thousands of farmers and the restriction of many farming communities to
forest or a new type of agriculture.