52 



THE APPLE 



Evaporation losses. A light shower followed by warm sunshine 

 may refresh the foliage of fruit trees, but its effect on the soil is 

 likely to be injurious. A brief, pelting rain followed by sunshine 

 forms a crust on the surface of most soils, and if this is not soon 

 broken up by cultivation it checks the free circulation of air in the 

 soil and also tends to increase the amount of water evaporated. 

 It has been found that the amount of moisture held by the soil, 

 the temperature of both soil and air, and the rate of wind motion 

 are the chief factors in the evaporation of water from soils. 



Jan. Mar. May July Sept. Nov 

 Feb. Apr. June Aug. Oct. 



1904 1905 



Fig. 72. Temperature and evaporation 



Relation between temperature and evaporation from a water surface at Tulare, California 



The results of experiments have shown that when water is 

 applied to the surface of orchard soils the loss by evaporation is 

 very great so long as the top layer remains moist. Even in light 

 irrigations this loss in forty-eight hours after the water is applied 

 may amount to from 10 to 20 per cent of the total. In order to 

 reduce this loss and to moisten the soil around the roots of trees, 

 the practice of running small streams of water in deep furrows 

 has become quite common. In applying water in this way the 

 topsoil remains at least partially dry, the bulk of the water soon 

 passes beyond the first foot, and the surface can be cultivated 

 soon after the water is turned off. 



