USE OF WATER BY SPEIXG WHEAT OX GREAT PLAIXS. 
17 
Figure 6 shows the water use on plat A at Amarillo, Tex., for the 
six-year period from 1911 to 1916, inckisive. The curves in this figure 
show why a high yield of wheat has never been obtained at this 
station. In three of the six yeai^ the wheat crop suffered for water 
from the time it commenced rapid growth until harvest. The^e three 
years all show a low rate of water use and a low yield. In the other 
three years there was enough moisture to enable the crop to make 
rapid growth for a time, but in each year the crop was short of water 
long before harvest and the yield was seriously reduced. In the 
history of these experiments there has not been a year at Amarillo 
when severe drought has not injured the crop before harvest, and 
consequently a high yield has never been produced. The reason for 
this lies largely in the high rate of water use from the time the crop 
begins rapid growth. It is evident that for the crop to have used 
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Fig. 6. — Diagram showing the use of water by the wheat crop on plat A at Amarillo. 
Tex., for the years from 1911 to 1916, inclusive. 
water until its harvest date either in 1911 ox in 1915 at the rate indi- 
cated during its early growth a supply of at least 22 inches would have 
been required. The average quantity of available water stored in 
the soil of plat A at the beginning of the crop season is less than 5 
inches. In order for the wheat crop to grow to maturity without 
drought injury, a precipitation of at least 15 or 16 inches cluring its 
growth period would be* necessary. The fact that such a precipita- 
tion is practically unknown gives at least one good reason why spring 
wheat is not adapted to that section of the Great Plains. 
Figure 7 shows the water use on plat C or D for the same years 
shown in Figure 6 for plat A. The water use on the two plats is 
much the same, though enough stored water was present in plat 
C or D in rnost years to keep the crop growing a little longer before 
drought injury comimenced. Tliis resulted nearlv everv year in a 
higher yield for plat C or D. The only exception shown is the year 
1915. In that year plat A used more water and produced a higher 
yield than plat C or D. 
21511"— 2.3 3 
