THEORY OF SOIL FERTILITY 201 



tied countries. If any such transference of 

 mineral material actually takes place to an 

 extent sufficient to maintain or increase the 

 productivity of more densely populated coun- 

 tries, then it is but reasonable to expect that 

 the productivity of the soil of the more re- 

 cently settled and more sparsely settled coun- 

 tries from which foodstuffs are exported would 

 show a falling off in productivity. From this 

 point of view the soils of the United States 

 might be expected to show some material de- 

 cline in productivity as a result of the enor- 

 mous amount of foodstuffs exported, while 

 the soils of Europe, to which these foodstuffs 

 mainly go, should show a corresponding in- 

 crease." 



"The largest average yield of wheat per 

 acre for any one year of the countries above- 

 named for the period reported on by the Bu- 

 reau of Statistics is as follows: 



Largest average yield of wheat in different European countries in any 

 year covered by reliable statistics 



Bushels 



Russia 11 .4 



Spain 14.9 



Italy 15.4 



Servia 19.4 



Austria 20 . 2 



Hungary 21.8 



France 22 . 7 



Roumania. . .22.8 



Bushels 



Switzerland 25.9 



Sweden 28.0 



Germany 30 . 3 



Netherlands 33.7 



Belgium 35.1 



Great Britain 35.8 



Ireland 37.8 



Denmark 44 . 7 



"The largest average yield of wheat for any 

 one year in several groups of States in the 



