HORTICULTURE 



117 



water companies of Riverside County, California. Here more or 

 less irrigation water is used every month of the year. In the fol- 

 lowing table is given the average duty of water per month in acre- 

 feet per acre under the same system from December 1, 1901, to 

 November 30, 1908, a period of seven years. The table also includes 

 the average monthly rainfall at Riverside, Cal., for the same period, 

 and adding the quantity of water applied in irrigation in any one 

 month to the rainfall of that month gives the total moisture received 

 by the soil. 



Water Used Under Riverside Water Company's System 

 (1901-1908). 



Evaporation Losses from Orchard Soils. A light shower fol- 

 lowed by warm sunshine may refresh the foliage of fruit trees, but 

 its effect on the soil is more likely to be injurious than otherwise. 

 A brief, pelting rain followed by sunshine forms a crust on the sur- 

 face 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. 



The results of experiments have shown that when the 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 irriga- 

 tions this loss in forty-eight hours after the water is put on may 

 amount to from 10 to 20 per cent of the volume applied. In order 

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

 practice of running small streams of water in deep furrows has be- 

 come quite common. In applying water in this way the top soil re- 

 mains 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. 



Soil Mulches in Checking Evaporation. The surface earth- 

 mulch (which can be secured only by cultivation) con- 

 serves the moisture stored in soil by checking capillary 

 action, and by preventing evaporation from all the soil except the 

 mulch itself; and it also permits air to enter the sub-soil freely. 

 Western orchardists can prevent the greater part of the evaporation 



