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. Theworkbegun at 
that time has been constantly added to until 24 stations were in opera- 
tion in 1916. Data from only 13 of these stations are here presented; 
those that have been operated less than four years are not included. 
The method of work 
|“ //// adopted was that of 
oe raising the different 
, 5 | j crops both in different 
, combinations or 
Z eee | 7 systems of rotation 
SLM, ae Z 2 y and under different 
777 Y Baa pees ns alge se Y methods of cultivation 
// YY yp BAK. Yj in systems of contin- 
Yyy Yl Yj uous cropping. Inno 
Yyy case have rotations of 
Y more than six years 
Y, in length been used. 
4 Those of even this 
Vp length have been tried 
only with sod crops. 
More of the work has 
been done with 3-year 
and 4-year rotations. 
7 soy Zi} AREA INCLUDED IN 
OK 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 
thewestern portions of 
North Dakota, South 
Dakota, Nebraska, 
Kansas, Oklahoma, 
and Texas, and the 
ten States and consists of about 400,000 square miles of territory. 
Its western boundary is indicated by the 5,000-foot contour. The 
location of each field station within the area isshown by a dot with- eastern portions of 
in a circle (©). 
Montana, Wyoming, 
Colorado, and New Mexico. 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- 
