DRY-FARMING 



ers of water pouring over the land, and a 

 few hours later to walk over perfectly 

 dry ground is a phenomenon familiar to 

 every farmer in the semi-dry zone. This 

 appalling waste is mainly due to hard 

 impenetrable soil in a word to surface 

 run-off ; and, secondly, to the sucking 

 power of a summer sun. 



Evaporation therefore is a factor 

 which should not be ignored in passing 

 judgment on the agricultural produc- 

 tiveness of any region. By the term 

 evaporation is meant the number of 

 inches of water which vaporizes or evapo- 

 rates from a clean water surface in a 

 freely exposed open tank during a given 

 period. Thus the annual evaporation is 

 the total number of inches of water which 

 evaporates during the year, just as the 

 precipitation is measured by the total 

 number of inches of water falling into the 

 tank, as rain or snow, during the year. 

 98 



