302 DRY FARMING 



sumption that there is a continuous upward movement of 

 soil water by capillarity of sufficient magnitude to materi- 

 ally affect crop growth will prove disappointing when 

 put to the test of actual field practice, as has been done 

 in the extensive investigations conducted during the past 

 fourteen years in the Great Plains by the Office of Dry 

 Land Agriculture. 



A careful study of hundreds of thousands of soil mois- 

 ture determinations fails to show any such movement. 

 The soils of the semi-arid regions undoubtedly do lose 

 large quantities of soil water, but this loss is undoubtedly 

 due almost entirely to some one, or to a combination of 

 two or more, of three factors, utilization by the growing 

 crop, transpiration from growing weeds, or loss from 

 internal evaporation and escape from the soil to the at- 

 mosphere in the form of water vapor. Only such methods 

 of moisture conservation as will prevent loss from these 

 sources are worth considering, so far as the water which 

 has actually entered the soil is concerned. Excessive run- 

 off may be retarded and the absorption of water by the 

 surface soil may be facilitated to a limited extent by 

 proper methods of surface tillage. But any method of 

 tillage calculated to prevent capillary rise and surface 

 evaporation of soil water in semi-arid regions will be use- 

 less except in so far as it stimulates the growth of crop 

 plants, destroys weeds or retards their growth, or checks 

 the escape of water vapor from cracks or other openings 

 in the soil. 



248. Farm Organization and Crop Rotations. As for- 

 age crops of some kind can profitably be grown at all 

 stations, they must occupy an important place in any 

 system of farming adapted to the Great Plains. Suf- 

 ficient live stock must be kept to convert these crops into 



