8 BULLETIN 1276, U. S. DEPARTMENT OF AGRICULTURE 
and cold winter temperatures, but they differ markedly in the dis- 
tribution of the precipitation. In the Great Plains area most of the 
precipitation falls in the spring and summer months, covering the 
chief growing period, while in the Great Basin area most of the pre- 
cipitation occurs during the winter months, when evaporation is low 
and plant growth is slow, so that more moisture is saved for the use 
of the crop. The average annual precipitation and the length of . 
the record, the altitude, and general soil type are shown in Table 2 
for each of the 15 experiment stations. 
GREAT PLAINS AREA 
The Great Plaims area extends from southern Texas northward 
into Canada and from about the ninety-eighth meridian wéstward 
to the Rocky Mountains. The elevation ranges from 1,500 to more 
than 6,000 feet. 
The climate is semiarid, the average annual precipitation varying 
from 14 inches in the northern and western portions to 25 inches in 
the southern and eastern portions. In general, the evaporation 
varies with the precipitation in this area, being highest in the south 
and lowest in the high elevations of the north and west. Thus the 
higher precipitation in the southern portion is of little advantage. 
Unfavorable climatic conditions, together with some injury from 
bunt (stinking smut), stem and leaf rusts, insects, and rodents, tend 
re keep the yields of winter wheat in the Great Plains area rather 
ow. 
High winds during the fall and winter frequently cause soil drifting 
and consequent injury to or loss of the wheat crop. Hot summer 
winds often cause premature ripening or deadening of the wheat 
pias resulting in shrunken kernels, lowered yields, and lowered 
ushel weight of the grain. Low winter temperatures, especially in 
the more northern States and at the higher altitudes in the western 
pqrion of the Great Plains, frequently cause winterkilling of the 
all-sown wheat. 
The chief limiting factor in wheat production is deficient moisture. 
The yields usually are largely dependent upon seasonal precipitation 
and the supply of soil moisture. Often the soil is so dry and pre- 
cipitation so slight that the wheat emerges very slowly after sowing 
and sometimes does not come up until the following spring. 
GREAT BASIN AREA 
The Great Basin area consists largely of elevated valleys and 
plateaus interspersed with mountain ranges. The average annual 
precipitation is less than in the Great Plains area, but successful 
wheat growing in the Great Basin is possible with less precipitation 
than in other parts of the United States. Here, as in the Great 
Plains, precipitation is the chief limiting factor in wheat production. 
Summer fallowing in preparation for winter wheat is commonly 
practiced, largely to conserve moisture. Winterkilling occurs only 
occasionally. Often the dry soil prevents the wheat from coming 
up until spring. Soil drifting caused by high winds occurs in the 
Great Basin, especially on the lighter types of soil. Rust causes 
ractically no loss to the wheat crop in the Great Basin area, but 
ee (stinking smut) is a very destructive and widespread disease. 
