USE OF WATER BY SPRIXG WHEAT OX GREAT PLAINS. 
25 
rear showed that the plat having the greater moisture content about 
ilav 1 gave the highest yield in 73 out of 93 cases. Very little 
correlation existed between the c^uantity of moisture stored and the 
yield in different years of the same plat. In other words, it was 
not possible to prove that 6 inches of stored water in the soil of a 
plat in one year was any more effectual in producing a good yield 
than 4 inches of water might be in another year. The precipitation 
was the deciding factor. However, when two plats were compared 
for the same year the plat having the greater quantity of stored water 
present was fairly certain to produce the higher yield. A plat with 6 
inches of stored water available was almost certain to produce a 
higher yield of grain than one having 4 inches of water. TTliile the 
J200 
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Fig. 8. — Diagram showing the total yield and ratio of pounds of water used to pounds of 
yield of wheat. The small circles are from data in Table 3. The crosses within circles 
show the averages by 1,000-pound yield groups, as given in Table 4. 
precipitation for the growing season is the deciding factor in wheat 
production, the quantity of stored water supplementing the rainfall 
has a decided bearing upon the yield of the crop. 
To facilitate comparison of these results with those obtained in 
controlled studies of water requirement, the ratio of the total water 
use to the total weight of crop harvested has been calculated and is 
given in the last column of Table 3. The correlation of the yield 
with these ratios is shown by dots in Figure 8. The yields of grain 
and straw in pounds per acre are charted as abscissa and the pounds 
of water per pound of crop as ordinates. The dots tend to arrange 
themselves in a curve showing increasing efficiency in the use of water 
with increasing yield. A reason for this is brought out under the 
succeeding heading, where it is shown that the consumption of a 
certain quantity of water is necessary before any yield is produced 
