THE FUNCTION OF WATER IN AGRICULTURE 245 



incapable of producing a crop, may be restored over 

 wide areas to a condition of great fertility. In other 

 words, it may be made to feed the growing plant. Thus 

 while artificial climate, irrespective of water supply, 

 must of necessity be confined to the narrowest areas, 

 a soil may be practically reconstructed over large areas 

 and economically utilized for the growing of crops. 



In all places where irrigation is possible such soils 

 may be made independent altogether of natural precipi- 

 tation. The quantity of water required for a growing 

 crop is enormous. We are familiar with the rapidity 

 with which the hot sun can dry a field, but the quantity 

 of water which the sun may take from the soil is by no 

 means so great as that which is exuded from the foliage 

 of the plant at the period of its most rapid growth. 

 Computations of the quantities of water which are thus 

 evaporated into the air from the leaves of plants are 

 necessarily largely estimations. Enough is known, 

 however, to make it certain that a rapidly growing crop 

 at the period of its greatest exuberance is a much more 

 potent factor in drying the soil than the sun's rays. 



PLANT FOOD IN SOLUTION". 



The plant food exists in a soil of ordinary content 

 of moisture in a state of solution in the soil moisture. 

 The particles of moisture are extremely small, but that 

 doesn't prevent them from becoming saturated with the 

 soluble materials of the soil if there are enough of them 

 in the soil to produce this saturation. The droplet thus 

 saturated is beyond the ken of the eye, but possibly 

 might be seen with a powerful microscope. As the 

 quantity of water in the soil diminishes, the quantity 

 of plant food in solution is decreased. In other words, 

 by evaporation of the particles of water the contents 



