CAMPBELL'S SOIL CULTURE MANUAL 125 



This illustrates exactly what is done on the soils o. 

 the semi-arid region to check evaporation. 



NOT LACK OF RAINFALL. 



The real difficulty in the semi-arid belt is not a lack 

 of rainfall, but the loss of too much by evaporation, and 

 this can be largely controlled by proper cultivation, at 

 least sufficiently to secure a good growth of crops every 

 year. It has been demonstrated by careful laboratory ) / 

 and field work by Professors King, Whitney, Hilgard, and H 

 others, that seven inches of rainfall is ample to grow a 

 good crop of any kind, providing the water is all utilized. 

 Measurements and records by the government weather 

 bureau have shown that in the more westerly portions 

 of the semi-arid belt the average rainfall is more than 

 twice as much as is needed, while a little further east it 

 is three and four times the necessary amount. 



The usual difficulty, if such we may call it, is the fact that 

 this rain does not always come just at the time the plants 

 most need it. This is the reason crops have failed and 

 the average investigator or observer of the existing con- 

 ditions in this great belt has drawn the conclusion that 

 there is not rain enough. We have lived in this belt of 

 country twenty-eight years, and have experienced all the 

 pros and cons, the ups and downs that the country is heir 

 to. Sixteen years of this time has been spent entirely 

 in the study of the soil, the movement of the moisture in 

 the soil, and that all-important question of storing the 

 rain waters. Our experience in these sixteen years has 

 been quite varied, but each and every year some new and 

 important fact has been brought out, all leading to the one 

 conclusion, that the rainfall can be stored in the ground, 



