Winter Irrigation of Deciduous Orchards. 211 



that the growth of weeds during summer was essential to the wel- 

 fare of the trees, since they kept the soil cool and thus sup- 

 posedly checked evaporation. 



PURPOSE AND SCOPE OF THE EXPERIMENTS. 



Previous to beginning the experiments, there existed consid- 

 erable difference of opinion among fruit-growers as to whether, 

 under the trying climatic conditions of southern Arizona, the irri- 

 gation of an orchard during winter, when the trees were dormant, 

 would materially lessen the amount of water that would need to 

 be applied during the succeeding summer. It was thought by the 

 writer that the question might be pretty definitely settled by ex- 

 periments covering two or three years. 



It is believed that sufficient data have been accumulated to 

 warrant publishing the results in bulletin form. Besides keeping 

 notes on the above-ground operations and conditions in the or- 

 chard, investigations have been made underground. The moist- 

 ure content of the soil has been determined from time to time, 

 and the changes caused by the application and by the withhold- 

 ing of water ascertained. Each phase of the subject, the above- 

 ground and the underground, will be taken up chronologically. 



ABOVE-GROUND OPERATIONS AND RESULTS. 



DURING 1898-99. 



The orchards upon the Station farm had been irrigated about 

 once a month through the summer of 1898, water having been 

 last applied about the middle of September. During the follow- 

 ing winter all were irrigated more or less thoroughly, but one 

 isolated orchard of about three-fourths of an acre was chosen for 

 special treatment and observation. The orchard consists of three 

 rows of peach trees and two rows of apricot trees, set 24 feet apart. 

 It had been planted in 1892, and the trees had, therefore, been 

 growing in their present situations seven seasons. The soil is a 

 clayey loam. 



Water was withheld from this small experimental orchard 

 from September until January 9, when the frequent application of 



