26 



BULLETIN 1004, TJ. S. DEPAETMENT OF AGRICULTURE. 



and that yields increase in proportion to the quantity of water con- 

 sumed above this. For those yields under 2,000 pounds per acre 

 there is a wide variation in the ratio of water used to yield. This 

 is not unexpected, as such yields do not represent normal growth 

 throughout the season or in many cases for any part of the season. 

 A further cause of divergence is the wide range of conditions from 

 the northern to the southern Piains covered by the data. There is a 

 much closer grouping for the yields above 2,000 pounds per acre, as 

 these are more nearly expressive of the requirements of normal 

 growth. 



The yields have been averaged in groups of 1,000 pounds and the 

 corresponding averages of the respective ratios determined. These 

 averages are given in Table 4 and shown in Figure 8 by crosses 

 within circles. No attempt has been made to determine a mathe- 

 matical expression of the relation evidenced in the data comprising 

 Figure 8. 



Table 4. — Ratios and total yields of icheat shown in Taole 3 arranged in yield 

 groups of 1,000 pounds and expressed as averages of such groups. 



Yield group. 



Number 

 in group. 



Yield 

 average. 



Ratio 

 average. 



Yield group. 



Number 

 in group. 



Yield 

 average. 



Ratio 

 average. 



1 to 1,000 pounds 



1,001 to 2,000pounds. 

 2,001 to3,000pounds. 

 3,001 to 4,000 pounds. 

 4,001 to 5,000 pounds. 



15 

 26 

 14 

 18 

 6 



Pounds. 

 793 

 1,413 

 2,444 

 3,492 

 4,323 



2,165 



1,588 

 951 

 814 

 754 



5,001 to 6,000 pounds 

 6,001 to 7,000 pounds 

 7,001 to 8,000 pounds 

 8,001 to 9,000 pounds 



1 

 2 

 

 1 



Pounds. 

 5,200 

 6,225 



686 



615 



8,650 



382 



While the ratios of water to yield obtained in this work range 

 higher than those obtained in controlled water-requirement studies, 

 such as those reported by Briggs and Shantz, 2 there are sufficient 

 reasons why this should be the case. * These field studies include all 

 loss from the soil itself which was excluded in physiological studies. 

 Our yields are relatively lighter, because they do not include an un- 

 determined residue that remains as stubble in the field plats from 

 which the crop is harvested with the self-binder but which was 

 included with the crop by clipping close to the ground in pot cul- 

 tures. This difference, however, is partly offset by the difference 

 between dry and air-dry material. Maximum efficiency was obtained 

 in pot cultures by constantly maintaining an optimum water content, 

 a condition which is the exception rather than the rule in the field. 

 The results all show that the efficiency of water is increased (the 

 water requirement reduced) by the maintenance of conditions that 

 favor maximum production. 



CORRELATION BETWEEN THE USE OF WATER AND THE YIELD 

 AT INDIVIDUAL STATIONS. 



A study was made of the correlation between water use and yield 

 at two stations — Edgeley, N. Dak., and North Platte, Nebr. These 

 stations were not selected because of their location but because re- 

 sults for more years were available at these stations than at any of 



2 Briggs, L. J., and Shantz, H. L. The water- requirement of plants. IT. S. Dept. Agr., 

 Bureau of Plant Industry Bui. 284, 49 pp., 2 fig., 11 pi. 1913. 



