CHAPTER II 



THE THEORETICAL BASIS OF DRY-FARMING 



The confidence with which scientific investigators, 

 famihar with the arid regions, have attacked the 

 problems of dry-farming rests largely on the known 

 relationship of the water requirements of plants to 

 the natural precipitation of rain and snow. It is 

 a most elementary fact of plant physiology that no 

 plant can live and grow unless it has at its disposal 

 a sufficient amount of water. 



The water used by plants is almost entirely taken 

 from the soil by the minute root-hairs radiating 

 from the roots. The water thus taken into the 

 plants is passed upwai'd through the stem to the 

 leaves, where it is finally eva]Jorated. There is, 

 therefore, a more or less constant stream of water 

 passing through the plant from the roots to the 

 leaves. 



By various methods it is possible to measure the 

 water thus taken from the soil. While this process 

 of taking water from the soil is going on within the 

 plant, a certain amount of soil-moisture is also lost 

 by direct evaporation from the soil surface. In 



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