104 Irrigation and Drainage 



maturity of such large crops under so clear a sky and in 

 spite of so long and continuous a period of drought, 

 while in western Kansas 25 to 38 per cent more rain- 

 fall, well distributed through the growing season, pro- 

 duces less than one -half the yield per acre. The yield 

 is certainly less than one-half, because the averages 

 used for Kansas are too large for the western section 

 of the state, whose rainfall has been brought into 

 comparison . 



While we are a long way from possessing the need- 

 ful data for the solution of this problem, some of the 

 factors are evident enough, and may be stated here. In 

 the first place, the rains of the sections of California and 

 of Washington under consideration fall in the cooler 

 portion of the year, when the air is more nearly 

 saturated and when the wind velocities are small, 

 while the sun is much of the time obscured by clouds. 

 All these conditions conspire to permit a large per 

 cent of the water which falls upon the ground to 

 enter it deeply, without being lost by evaporation, 

 while a deep, retentive soil serves to prevent loss by 

 drainage. 



In western Kansas, on the other hand, where the 

 rain falls largely in the form of showers in the heated, 

 sunny season of the year, and where the wind veloci- 

 ties are high and the air extremely dry, it is plain that 

 a much larger per cent of water falling as rain must 

 be at once lost by evaporation from the surface of the 

 soil, before it has had an opportunity to enter it deeply 

 enough to be retained by soil mulches. 



In the second place, a frequent surface wetting of 



