Page 26 



BETTER FRUIT 



April 



ninety-five per cent of the total falls 

 between November and J\Iay, inclusive. 



The most reliable, and in many ways 

 the most valuable, records pertaining to 

 duty of water on orchards have been 

 obtained by the water companies of 

 Riverside County, California. Here more 

 or less irrigation water is used every 

 month of the year. Figure 25 is a 

 graphic representation of the average 

 amount of water used per month in a 

 period of seven years by the Riverside 

 Water Company in irrigating about 

 9,000 acres, of which nearly 6,000 acres 

 are planted to oranges and the balance 

 to alfalfa. The figures given in the dia- 

 gram represent depth in feet over the 

 surface watered. In the following 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 aver- 

 age monthly rainfall at Riverside, Cali- 

 fornia, for the same period, and adding 

 the quantity of water applied in irriga- 

 tion in any one month to the rainfall of 

 that month gives the total moisture 

 received by the soil: 





Average 





Total 





depth 



Average 



water 





per acre 



rainfall 



applied 



Month 



Feet 



Feet 



Feet 



Deceml^er 



0.159 



0.109 



0.268 



January 



12.3 



.170 



.293 



Fel^ruary 



046 



.190 



.236 



March 



078 



.316 



.394 



April 



177 



.068 



.245 



May 



291 



.023 



.314 



Tune 



274 



.003 



.277 



July 



272 



.002 



.274 



August 



269 



.000 



.269 



September 



243 



.015 



.258 



October 



189 



.043 



.232 



November 



169 



.073 



!242 



Totals 



2.29 



1.01 



3.30 



A light shower followed by warm sun- 

 shine 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 surface of most 

 soils, and if this is not soon broken up 



by cultivation it checks the free circula- 

 tion 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 tempera- 

 ture of both soil and air, and the rate of 

 wind motion are the chief factors in the 

 evaporation of water from soils. The 

 influence of moisture is shown in the 

 following figures, obtained from tank 

 experiments made at Tulare, California, 

 covering the period from June 1.5 to Sep- 

 tember 15, 1904: 







Atnoiint of 











water applied 



Loss by evaporation 







Inches 



Inches 



Per cent 



Tanks 



1 and 2 . . 



0.0 



0.45 





Tanks 



3 and 4 . . 



3.3 



3.5 



106.0 



Tanks 



5 and 6 . . 



4.9 



4.6 



94.0 



Tanks 



7 and 8 



6.6 



5.5 



83.6 



Tanks 



9 and 10 



8.3 



6.6 



80.0 



Tanks 



11 and 12 



9.8 



7.9 



79.5 



The results of other 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 

 irrigations this loss in forty-eight hours 

 after the water is put on may amount to 

 from ten to twenty per cent of the vol- 

 ume 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 become quite common. In applying 

 water in this way the top soil remains at 

 l,east 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. 



The well known effect of temperature 

 on evaporation is shown in Figure 26. 

 The dotted line shows the mean monthly 

 temperatures at Tulare, California, from 

 January 1, 1904. to December 31. 1905, 

 and the solid line the monthly evap- 

 oration from a water surface for the 

 same time. 



The effect on evaporation of a layer 

 of dry granular soil when placed above 

 moist soil has been shown by a series of 

 experiments conducted in tanks by irri- 

 gation investigations of this office. These 

 tanks are water-jacketed and placed in 

 the open under normal conditions as 

 regards sunshine, wind and temperature. 

 Each tank holds about three-fourths of 

 a ton of soil, and is weighed at stated 

 intervals in a manner shown in Fi.gure 

 27. The results of experiments made at 

 Davis, California, in 1908 were as follows: 



Tanks 1 and 2, no mulch — Average weight of 

 tanks September 1, 1,104.7 pounds; total loss for 

 32 days, September 1 to October 3, 33.25 and 35.93 

 per cent. 



Tanks 3 and 4, 3-inch mulch — Average weight of 

 tanks September 1, 1,090 pounds; total loss for 32 

 days, September 1 to October 3, 14.25 and 15.17 

 per cent. 



Tanks 5 and 6, 6-inch mulch — Average weight of 

 tanks .September 1, 1,082 pounds; total loss for 32 

 days, September 1 to October 3, 5.75 and 6.12 

 per cent. 



Tanks 7 and 8, 9-inch mulch — Average weight of 

 tanks September 1, 1.085.2 pounds; total loss for 

 32 days, September 1 to October 3, 0.75 and 0.80 

 per cent. 



l-iGUHi- IS— .\i.\KI.\C, I'L'KROWS IN ORCHARD 



