Arizona Agricultural Experiment Station 689 



THE EFFECT OF TEMPERATURE AND HUMIDITY 



The purpose of this experiment, which is being conducted 

 in the Camel Back district of the Salt River Valley, is to de- 

 termine the effect of temperature and atmospheric humidity on 

 citrus trees, as reflected through intercultural practices. Stand- 

 ard meteorological instruments consisting of air and soil ther- 

 mographs, hydrographs, and atmometers have been placed in 

 two adjoining orchards, one with clean cultivation, and the 

 other with an alfalfa cover crop. Accumulated data at present 

 indicate a difference in both atmospheric and soil tempera- 

 tures of approximately five to six degrees F., the cover-cropped 

 orchard having the lower temperatures. Hydrographic records 

 show the atmospheric humidity to be approximately fifteen 

 percent higher in the orchard containing a cover crop ; whereas 

 the atmometer readings show a correspondingly lower percent- 

 age of evaporation. 



DATE STUDIES 



Progress on this project has been considerably retarded on 

 account of the necessity for "torching" in order to control an 

 outbreak of scale, Parlatoria blanchardi, which has occurred at 

 both the Tempe and Yuma stations during the past year. The 

 general condition of the orchard at Tempe, however, is quite 

 satisfactory, as the palms, since the beginning of warm weather, 

 have recovered very rapidly from the effect of the "torching" or 

 burning. The stronger trees have been allowed to carry from 

 two to three bunches of fruit. It might be noted that the 

 weaker trees failed to set fruit well, even when the flower 

 clusters were pollinated. The orchard at Yuma has not recov- 

 ered so rapidly from the treatment, and in fact several valuable 

 palms died during early spring. This orchard was "torched" 

 later in the summer than the Tempe orchard, giving the palms 

 less time to recuperate before winter, which may account for 

 the weakened condition of many of the palms. 



PROPAGATION OF OFFSHOOTS 



During the month of May eighty offshoots of the Deglet 

 Noor variety were taken from palms at the Yuma Station and 

 set directly in the field on the Yuma Mesa, in an effort to deter- 

 mine the practicability of this method of propagation where 



