USE OF SOIL MOISTURE BY PLANTS 121 



concentrated. Thorough and careful plowing results in a 

 diminished rate of loss of water from cropped soils. 



86. Cultivation. The frequent cultivation of the soil, 

 as discussed in Chapter III, has for its purpose the reduc- 

 tion of the direct evaporation of water from the soil. 

 It has, however, a number of other beneficial effects of 

 high importance to the irrigation farmer. For example, 

 cultivation diminishes the rate at which plants take water 

 from the soil, and further, as will be shown later, it even 

 diminishes the quantity of water required to produce a 

 given quantity of dry matter. Cultivation is essential 

 in irrigation agriculture because it diminishes the direct 

 evaporation from the soil and because it reduces the 

 quantity of water transpired by plants. It is a practice 

 that should be observed faithfully by the farmer through- 

 out the season. After every rainfall and after every irri- 

 gation, just as far as possible from spring until fall, the 

 soil should be carefully stirred by the farmer. The cost 

 of such treatment will be more than paid for in the greater 

 yields of crops, and hi the greater producing power of 

 water. 



87. Manuring. It is quite evident, from what has 

 been said already, that manuring, or the adding to the 

 soil of plant-foods, under a given rate of growth will tend 

 to reduce evaporation. This is another argument in behalf 

 of manuring a practice which, unfortunately, has not 

 been carefully observed by the irrigation farmers of 

 America. As time goes on and water becomes more 

 precious, and the population of the arid region increases, 

 the art of manuring, whether with natural or artificial 

 fertilizers, will acquire a greater and greater importance. 



88. Vigor of plant. The rate of loss of soil moisture 

 due to plants depends very largely upon the vigor of the 



