VERTICAL FARMING 



51 



much stronger capillary pull, the movement is much slower, 

 but may take place over greater distances against gravity. The 

 amount of moisture moved in this way decreases as the limit 

 of distance is reached. 



In addition to the texture, the structure of a soil has an im- 

 portant part in governing the capillary movement. The better 

 granulated a heavy soil, the greater the pore space and conse- 

 quently the greater the pull. Additions of humus materially 

 increase the capillary pull as well as the reservoir capacity of a 

 soil. In a puddled soil the movement is very slow and the 

 amount of water moved very small. The denser the soil be- 

 comes, the slower the movement. 



Dry layers of soil break off the capillary pull on account of 



the coating of the soil particles being of _^ _ 



such a nature that they resist wetting. It 

 is this fact that makes the effectiveness of a 

 dry dust mulch, in holding the water below 

 the surface and not allowing it to rise to the 

 surface and be lost by evaporation. Capil- 

 lary movement is much faster in wet or 

 moist soils than in dry ones, so it is advis- 

 able at all times to preserve some moisture 

 in the soil if only for its benefits in a rapid THE CAPILLARY 

 equalization of the moisture content when RISE OF MOISTURE 

 water is applied. The ratio of the move- CHECKED BY A 

 ment in wet and dry soils has been shown DUST MULCH 

 to be as high as I to 4. 



This upward movement continues to the surface and when 

 allowed to go unchecked will result in all the movable moisture 

 being pulled up and lost by evaporation. The rate of evapora- 

 tion of moisture from the surface is governed largely by tem- 

 perature and wind velocity. When water is stored at great 

 depths in the soil it is harder for it to be pulled to the surface 

 and lost. This surface less at times approximates an amount 

 equal to a sheet of water 5 inches deep, over the whole surface 

 in a month. A handy example of the upward movement of 

 water and a check to its loss can be observed by turning over an 



