THE MOISTURE PROBLEM 79 



of "run off" is largely determined by (1) the topography 

 of the land, and (2) the openness or receptivity of the 

 soil. 



The topography cannot be altered but some loss of 

 water may be prevented by tilling crosswise of the main 

 slopes. The more open the soil is at the time of the 

 heavy rains or when the snow is melting the more 



Fig. 27. — Wheat Under Irrigation near Strathmore, Alberta. 



moisture it will take in and the less "run-off" there will 

 be. 



The storage of moisture in "old" land is accom- 

 plished by : 



1. (a) Fallowing the land once in two, three, four or 



five years, depending upon the average pre- 

 cipitation and evaporation, 

 (b) Plowing or otherwise cultivating the fallow 

 early to lessen the possible "run-off" after 

 heavy rains. 



2. Using such intertilled crops as may not require all 

 the water, thus permitting of the storage of some; 



3. Using crops that may be harvested early, thus per- 



