9 BULLETIN 595, U. S. DEPARTMENT OF AGRICULTURE, 
States Department of Agriculture began field work in the investigation 
of methods of crop production in this areain 1906. Theworkbegunat 
that time has been constantly added to until 24 stations were in opera- 
tion in 1916. Datafrom only 13 of these stations are here presented; 
those that have been operated less than four years are not included. 
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ten States and consists of about 400,000 square miles of territory. 
Its western boundary is indicated by the5,00U-foot contour. The 
location of each field station within the area is shown by a dot with- 
in a circle (©). 
Colorado, and New Mexico. 
The method of work 
adopted was that of 
raising the different 
crops both in different 
combinations or 
systems of rotation 
and under different 
methods of cultivation 
in systems of contin- 
uous cropping. Inno 
case have rotations of 
more than six years 
in length been used. 
Those of even this 
length have been tried 
only with sod crops. 
More of the work has 
been done with 3-year 
and 4-year rotations. 
AREA INCLUDED IN 
THESE INVESTIGA- 
TIONS. 
The area covered by | 
these investigations is 
shown in figure 1 and 
consists of about 400- 
000 square miles of 
territory. It includes 
the western portions of 
North Dakota, South 
Dakota, Nebraska, 
Kansas, Oklahoma, 
and Texas, and the 
eastern portions of 
Montana, Wyoming, 
As no varieties of winter wheat 
have yet been found which are able to survive the winter in North 
Dakota, this crop is not included in the work at the North Dakota 
stations. 
The fact that limited rainfall is the determining factor in 
crop production is responsible for a general uniformity in condi- 
