26 BULLETIN 1458, U. S. DEPARTMENT OF AGRICULTURE 
methods and commercial fertilizers, a considerable increase in pro- 
duction has been realized as a result of the rising acre-yields. West 
of the Mississippi, Lowa stands out as an example where an increas- 
ing use of improved practices has brought increasing yields per acre. 
In both the spring-wheat and the winter-wheat regions of the West, 
owing to the fact that extensive production methods still continue to 
be most profitable from an economic viewpoint and as a result of 
the expansion of the crop area onto drier lands, crop yields have 
remained either stationary or have declined to a lower level. 
As far as indicated by the history of crop yields, both in various 
European countries and now in the United States, there has been a 
well marked trend away from extensive agricultural methods and 
toward the use of scientific methods of increasing soil productivity. 
Forecasting the future may indeed be hazardous, but it appears 
safe to predict that developments in the forthcoming decades, just 
as in the past, will depend to a great extent on the prices of agri- 
cultural products. Rising prices of food products normally would 
result in increasing intensification and a higher level of soil pro- 
ductivity through the wider use of better cultivation methods, de- 
velopment of suitable rotations, including the growth of legumes, 
more efficient use of crop residues and animal manures, greater use 
of commercial fertilizers, and the more common use of selected seed. 
A period of falling prices of agricultural products may temporarily 
arrest the advance toward higher standards of production, but the 
increasing demand of our steadily growing population for food 
must ultimately result in a, level of prices that will economically 
justify the wider use of improved methods of production. It appears 
probable, therefore, that the general trend of acre-yields of the crops 
will continue upward for a considerable period. 
