16 DRY-FARMING 



results tend to be somewhat higher than those ob- 

 tained in Europe, but the difference is smalL 



It is a settled principle of science, as will be more 

 fully discussed later, that the amount of water 

 evaporated from the soil and transpired by plant 

 leaves increases materially with an increase in the 

 average temperature during the growing season, and 

 is much higher under a clear sky and in districts 

 where the atmosphere is dry. Wlierever dry-farm- 

 ing is likely to be j^racticed, a moderately high tem- 

 perature, a cloudless sky, and a dry atmosphere are 

 the prevailing conditions. It appeared probable, 

 therefore, that in arid countries the amount of water 

 required for the production of one jjound of dry mat- 

 ter would be higher than in the humid regions of 

 Germany and Wisconsin. To secure information 

 on this subject, Widtsoe and Merrill undertook, in 

 1900, a series of experiments in Utah, which were 

 conducted upon the plan of the earlier experimenters. 

 An average statement of the results of six years' 

 experimentation is given in the subjoined table, 

 showing the number of pounds of water required for 

 one pound of dry matter on fertile soils : — 



Wheat 1048 



Com 589 



Peas 1118 



Sugar beets . 630 



These Utah findings support strongly the doctrine 

 that the amount of water required for the produc- 



