32 VERTICAL FARMING 



The water required by a field of any of the ordinary field crops, 

 if spread over the surface, would cover it to a depth of several 

 inches, sometimes as much as a foot or more. This is only the 

 water used by the plant itself, and does not include the amount 

 that is lost by being evaporated or that passing too deep into the 

 soil to be drawn back to the roots. In addition, a plant cannot 

 take all of the moisture out of the soil in the range of its roots. 

 In irrigated districts the amount of water applied to and 

 absorbed by the soil" often reaches an amount equal to three 

 feet, and in some localities more. 



This water used by the plant or lost by evaporation from the 

 soil during rainless days must all come from the soil, and shows 

 what care must be exercised in storing and holding all that is 

 possible. 



Water and Soil Temperature. A uniform soil temperature 

 is essential to the best growth of crops, and a soil properly sup- 

 plied with moisture will change its temperature very slowly, 

 while a dry, parched soil will quickly heat up during the day and 

 cool off again as rapidly at night, and the crops will suffer 

 accordingly. Coarse soils retain only a relatively small amount 

 of moisture and are warm and early. Fine soils, like the clays, 

 retain much more water and are cooler and later in the spring. 



Storing Water. Where irrigation is practised, reservoirs 

 are used to store and hold water, but in most of the states this 

 method is inadvisable. The best place to store the water for 

 use in time of drouth is in the soil itself, by converting the sub- 

 soil of every acre into its own reservoir. This large storage 

 may be assisted and encouraged in several ways. The first thing 

 to do is to be sure to get the rain water down into the soil 

 instead of allowing it to be wasted by running off on the sur- 

 face, because it cannot enter a hard or impacted soil readily, if 

 at all. Such soils may be found to be dry even after a heavy 

 rain. In " dry farming," and also in farming where the rainfall 

 is heavier, some practise rough plowing before the seasons of 

 heavy rain to increase the absorption of rain water, and later 

 harrow or drag the surface to form a mulch and prevent loss 



