ON DRY-FARMING INVESTIGATIONS IN THE UNITED STATES. 269 
also increases in a corresponding manner, so that the ratio of the 
water-requirement to the daily evaporation is approximately constant. 
Montgomery and Kiesselbach* have shown that maize grown in a 
dry house and in a humid house varied in its water-requirement 
exactly in proportion to the relative evaporation-rates in the two 
houses. 
The water-requirement is not, however, always proportional to the 
evaporation. Other factors such as temperature may have a profound 
influence in determining the development of the plant. This may be 
illustrated by comparing the water-requirement of wheat and sorghum 
in Colorado and in Northern Texas (Table II.).?_ When the difference 
in evaporation is considered, sorghum is seen to have made a more 
efficient use of its water-supply in Texas than in Colorado, while the 
reverse is true in the case of wheat. 
TasLE II.—Comparison of the Relative Evaporation and of the Relative 
Water-requirement in the Great Plains in 1910 and 1911. 
| E ti | Water-re- 
| vaporarion quirement 
Station Year Crop Growing period re = | 
ela- | ela- 
Actual tive (Actual] tive 
Akron, Colo. .' 1910 | wheat | April 18-Aug. 2 | 27:7 | 100 664 | 100 
Amarillo, Tex. April 5—July 19 | 34:0 | 122 | 853 128 
Akron, Colo. .' 1910 sorghum | May 25-Sept. 28] 33:0 | 100 356 | 100 
Amarillo, Tex. May 10-Aug. 28 | 37:7 | 114 | 359 | 101) 
Akron, Colo. .| 1911 | wheat | May 13-Aug. 2] 248 100 | 468 | 100 
Dalhart, Tex. . April 25—-July 18 | 28-5 | 115 | 673 | 148 
Akron, Colo. .}| 1911 |sorghum | May 12-Sept. 4] 35:0 | 100 | 298 | 100 
Dalhart, Tex. . May 14-Sept. 12] 41:9 | 120 | 313 | 105 
Influence of the Distribution of Rainfall on Farm Practice. 
The different distribution of the rainfall in the Intermountain district 
and the Great Plains has led to interesting differences in the farm 
practice of these regions. 
Spring wheat is not a successful crop in the Intermountain district 
for two reasons: (1) The land cannot be fitted for sowing until late in 
the season, owing to the spring rains; and (2) the driest part of the 
season occurs when the spring wheat crop is maturing. A large acreage 
of winter wheat is, however, grown. In fact, the dry-farming activities 
of this section are devoted almost wholly to the growing of winter wheat. 
The stubble is. not usually ploughed until spring, the land being very 
dry and hard in the fall. The stubble also keeps the winter snows from 
drifting and thus holds the precipitation on the land. As soon as the 
8 Studies in the Water-requirement of Corn, Nebraska Agricultural Experiment 
Station, Bulletin 128, 1912. 
7 Briggs, L. J., and Shantz, H. L., Water-requirement of Plants, I., U.S. Depart- 
ment of Agriculture, Bureau of Plant Industry, Bulletin 284. p. 45 
