OATS IN THE GREAT PLAINS AREA. 3 
different methods of cultivation in systems of continuous cropping. 
In do case have rotations of over 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 INVESTIGATIONS. 
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 parts of North Dakota, South Dakota, Nebraska, Kansas, 
Oklahoma, and Texas, and the eastern portions of Montana, Wyo- 
ming, Colorado, and New Mexico. The fact that the determining 
factor in crop production is the limited rainfall is responsible for a 
general uniformity in conditions throughout the area. There is, 
however, a wide range of soil, climatic conditions, and altitude. The 
lowest station is Edgeley, N. Dak., with an altitude of 1,468 feet and 
the highest is Archer, Wyo., with an altitude of 6,012 feet. The 
length of the growing season for oats is naturally much the same 
throughout the area, but there is a variation of approximately a 
month to six weeks in the respective dates of seeding and harvesting 
oats, the southern section using the earlier dates. 
CLIMATIC CONDITIONS. 
The area is characterized by a varying amount of annual and 
seasonal precipitation, with very uncertain distribution. Years of 
relatively high precipitation with favorable distribution may be 
followed by years of relatively low precipitation with very unfavor- 
able distribution. It may be said that the uncertainty of the dis- 
tribution rather than the total amount of rainfall received is the factor 
that makes crop production hazardous. In connection with this 
work, complete climatic data have been obtained. It is not practi- 
cable, however, to give them in this publication. Table I shows the 
minimum, maximum, and average annual and seasonal rainfall and 
the seasonal evaporation at each station for the years for which the 
yields are here reported. By seasonal is meant the precipitation or 
evaporation for the period between the average time of seeding and 
the average time of harvesting. No attempt is made here to show any 
of the other climatic factors or the amount of water already in the 
soil at seeding time, any one of which may have an important influence 
on yields. The annual precipitation as here given is not the annual as 
determined from the complete record, but is the average annual 
precipitation of the years whose results are under study. 
