Winter Irrigation of Deciduous Orchards. 231 



loss of water was comparatively — at first thought surprisingly — 

 small. The total loss from the 25 feet was but a little over a 

 fifth of what it was during the previous two and one-fifth months, 

 or an equivalent of only about three inches in depth. The irri- 

 gating water applied June 24 did not affect the above results, as 

 only three-fifths of the orchard was irrigated at that date, and the 

 samples were taken from the unirrigated portion. Neither could 

 the 4.76 inches of rain that fell in the interval affect the moisture 

 content below the upper six inches, as it fell in twelve different 

 showers, less than an inch falling during any one da}'. The 

 only effect of these summer showers upon the soil, in the vicinity 

 of Phoenix, is to wet a few inches of the surface that dries out 

 within a few hours or days. There is thus formed a crust that 

 not only promotes capillary action and the consequent loss of wa- 

 ter that was already present, but excludes air from the subsoil. 

 Even the part of the orchard irrigated received little benefit from 

 the water applied, as the soil was wet to a depth of only about 15 

 to 18 inches, and was as dry as before irrigation within three 

 weeks thereafter. 



When Trees Use the Most Water. 



The great comparative loss of water during the months of 

 spring and early summer indicate that this is the period when 

 orchard trees naturally use, and consequently need, the major 

 part of their water supply. During this period of rapid growth, 

 therefore, water should be available in abundance. But by ref- 

 erence to the data given in the introduction, it will be seen that 

 during this period the supply of irrigating water is usually low. 

 The above facts, disclosed by the moisture determinations, em- 

 phasize very strongly the importance of filling the subsoil with 

 water during the winter, when the supply is comparatively 

 abundant. 



Losses of Water During Entire Season. 



From September 30 to December 10 there was little change 

 in the moisture content, the total loss from the 25-foot column of 

 soil being but about five pounds. As the trees remained in ex- 

 cellent condition until they shed their leaves in November, all the 



