VERTICAL FARMING 



PART V 



The Movement of Moisture and the 

 Feeding Zone of Roots 



The movement of moisture in the soil is of the utmost impor- 

 tance to plants. It is first necessary that the water received 

 from rain or irrigation should move downward through the 

 soil, leaving behind only such as is held by capillary attraction. 

 The excess should move out of the soil and into the drainage. 

 This movement of moisture is entirely one of gravity. Water 

 moving in this way is called " free water." 



Movement of Water by Gravity. In order to get the water 

 down into the subsoil and prevent its running away as surface 

 drainage, or standing on the surface and stopping all possi- 

 bilities of air circulation through the soil pores, it is essential 

 that it move downward very soon after it is deposited on the 

 surface. This movement depends on the openness of the soil. 

 Sometimes in a sandy soil the water soaks into the soil too 

 rapidly and too much drains away, but such is not the case with 

 clay and other dense soils. In such soils the pores are naturally 

 small and the water is held back. The movement can be 

 hastened by tilling or stirring the soil to the depth to which it 

 is desirable to carry the water. The deeper this can be made 

 effective the better, and so it is very apparent that soils where 

 the water is likely to stand on the surface are in need of the 

 deepest practical tillage. As the free water clogs the pores and 

 stops many of the soil processes, the plants do not draw their 

 moisture from it, but get it instead from the smaller capillary 

 supply left behind. 



