USE OF WATER BY SPRING WHEAT ON GREAT PLAINS. 



17 



Figure 6 shows the water use on plat A at Amarillo, Tex., for the 

 six-year period from 1911 to 1916, inclusive. The curves in this figure 

 show why a high yield of wheat has never been obtained at this 

 station. In three of the six years the wheat crop suffered for water 

 from the time it commenced rapid growth until harvest. These 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 or 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 during 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 most years to keep the crop growing a little longer before 

 drought injury commenced. This resulted nearly every 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°— 23 3 



