24 THE BOOK OF FORESTRY 
by means of fertilization and the use of proper rotations, 
to build up the soil which they have long drawn upon, 
the future of this nation will be extremely dark. 
Of the land now idle through lack of rain it is believed 
that fully 400,000,000 acres can be made productive by 
the use of irrigation, or dry farming methods but how 
much more practical it would be to make land now 
owned and tilled yield maximum crops by the appli- 
cation of commonsense principles. That the population 
of this country will double within the next seventy-five 
years seems more than possible and to feed so many 
hungry mouths will require the best use of every acre 
of land suited to tillage. It is only necessary to stop the 
constant drain upon the land and by practicing systems 
of agriculture which will at least maintain the soil 
fertility to keep this country the food warehouse of 
the world. 
Not only is soil fertility lost through shiftless agricul- 
ture but great waste is caused by permitting erosion 
and beating rains to rob the land of its richness. Dr. 
Shaler estimated that no less than two hundred square 
miles of fertile farm land are laid waste each year as 
result of the action of water and when it is realized 
that the Mississippi River carries away 400,000,000 
tons of sediment, representing the most fertile portion 
of the fields, some conception of the total loss may be 
gained. The remedy consists In maintaining a proper 
balance between agricultural and forest land. Land 
which is too steep should not be tilled but should be 
kept under forest cover as the tree roots bind the soil 
together and prevent it from being gullied by the rains 
and melting snows. In some places where bench lands 
are tilled it may be advisable to leave occasional strips 
of forest land between the tilled fields as the trees and 
