USE OF WATER BY SPRING WHEAT ON GREAT PLAINS. 



25 



year showed that the plat having the greater moisture content about 

 May 1 gave the highest yield in 73 out of 93 cases. Very little 

 correlation existed between the quantity 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. While the 



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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 



