8 AGRICULTURE TN THE SEMIARID GREAT PLAINS. 



with its recurring periods of heat and cohl, is responsi))le for our being 

 the busy, husthng nation that we are."^ 



Settlers in new countries, and especially in the dry regions, have 

 often been misled by giving too little attention to climatic conditions. 

 They have found a fertile, easily tilled soil, and without regard to 

 climate have assumed that good crops must be the reward of 

 cultivation. 



NATURAL FACTORS OF PLANT GROWTH IN THE GREAT PLAINS 



FIXED. 



Of the chmatic factors, rainfall and evaporation are the most impor- 

 tant in the semiarid region, because the most faulty. The saying that 

 ''rainfall fohows the plow" has, in its effect, been one of the worst 

 deceptions ever foisted upon a credulous public. This idea has been 

 the undoing of more plains settlers than has drought itself. If tiie 

 people had realized that the dry country would always be a dry 

 country many who have settled in the semiarid regions would never 

 have gone there, and those who did go, understanding the hard 

 conditions, might have risen to the emergency and long ago have met 

 the necessity, as did the settlers in Utah and Washington, instead of 

 waiting in the vain hope that Nature would take pity on them and 

 reward their puny efforts by an increase in precipitation. Space does 

 not permit a discussion here of the fixedness of climate, but all students 

 of meteorology now agree that the climate is unchangeable, at least 

 within the limits of a single generation.- There are fluctuations from 

 year to year and more or less cyclical changes which give periods of 

 dry years followed by periods of wet years, but the average of a long 

 period of years is practically stable. These fluctuations, although 

 very irregular, lie between fairly well-defined limits as regards total 



variation. 



The mainf actors afl'ecting evaporation from an open water surface are 

 the relative humidity of the atmosphere, or the proportion of moisture 

 in the air compared to what it can hold, the wind velocity, the tem- 

 perature of the air and of the water at the surface, and the air pressure. 

 Evaporation from the soil, however, is affected not only by these 

 factors, but also by the character and condition of the soil and by 

 the ])lant growth thereon. Soil conditions and plant covering are 

 largely under the farmer's control. 



The soil in its native state is, like the climate, unchangeable so far 

 as the ordinary limits of time are concerned, but under cultivation 

 very important temporary changes may be brought about. ^ 



> Ball, Frank Morris, of fhr^ dnpartmont of poclogy. ITnivcrsity of Minnesota, in Monthly Weather 



Review, May, 19(;G. 



2 For a discussion of this subjctl tlic rcu.lor is referred to tlie Veurtjoolv of llie U. S. Dept. of Agriculture 

 for 1008, p. 289; Bulletin D, U. S. Weather Bureau; and Mbnthly Weather Review, May, 1900. 



3 See I$ulletin 55, Bureau of Soils, pp. 61, 71, and 70. 



215 



