THE MONTHLY BULIiETlN. 



33 



TABLE No. 1. 



Pounds of water evaporated by the growing plants. 



Per pound of dry matter.* 



England, 

 pounds 



Utah 

 pounds 



Wisconsin, 

 pounds 



Beans 



Wheat 



Peas 



Red clover 



Barley 



Corn 



214 

 225 

 235 

 249 

 262 



Sugar beets 



Maize 



Potatoes ... 

 Oats 



272 

 432 

 357 



The average rainfall in Southern California is hetween 15 and 24: 

 inches. ]f all the moisture from a 24-inch season were taken into the 

 soil and none were lost from seepage, evaporation, and surface runoff, 

 it would mean a supply of 5,445,000 pounds per acre. This looks like 

 an ample supply, but extensive experiments by the agricultural experi- 

 ment stations show that not more than 50 peF cent enters the ground as 

 available moisture, and of this supply not more than 50 per cent ever 

 reaches the crop. 



In general, the success of dry land crops is due to their ability to exist 

 on very little water. Consequently, if the transpiration from the leaves 

 is reduced the crop stands a better chance of giving satisfaction. There 

 are two methods of controlling transpiration and these methods relate 

 to the weed problem as well as to the crops individually: (a) Clean 

 cultivation and plenty of room for plants to gather all available mois- 

 ture; and (&) clean cultivation plus reduction of the leaf growth. 

 Many orchards are planted too thickly. Plants can be greatly helped 

 by reducing the amount of growth per unit of soil mass. 



An acre of soil to the depth of one foot w^eighs approximately 1,800 

 tons. If 25 per cent of this is moisture there would be 450 tons of 

 water per acre. A well tilled soil in good physical condition will hold 

 this amount of water in each of the fii-st three feet, and if carefully 

 conserved, will answer all the requirements for the best California 

 growing season without any irrigation at all. Thus we see how impor- 

 tant the moisture supply is, and the necessity of storing up reserve in 

 the soil. Every means should be employed by the live farmer and 

 orchardist to get the maximum growth from his natural water supply, 

 and to prevent the expense of irrigation. 



It has been said that the beginning of wisdom in irrigation is the 

 economic utilization of the natural precipitation. It may also be said 

 that the basis of scientific irrigation is the conservation of useful mois- 

 ture in whatever form it may have been added to the soil. The 

 efficiency of soil water may be measured by the actual useful work 

 performed by anv given quantity. To increase the efficiency and to 

 maintain a favorable supply during the long growing season, requires 



*W. L. Power.s, Irrigation. 



