WINTER IRRIGATION OF DECIDUOUS 

 ORCHARDS. 



By A. J. Mc CI ate hie. 



INTRODUCTION. 



During December, 1898, experiments were begun at the Sta- 

 tion farm near Phoenix to test the effects of the irrigation of de- 

 ciduous fruit trees during the winter months. The difference in 

 opinion among orchardists as to the value of winter irrigation 

 suggested the making of carefully conducted experiments along 

 this line. The question as to how best to maintain orchards in a 

 thrifty state under the somewhat trying conditions existing in 

 the valleys of Arizona was one of much importance to the fruit 

 interests of the territory. That those not familiar with the region 

 may understand the bearing that the experiments outlined in this 

 bulletin have upon our problems of orchard culture, some state- 

 ments concerning the climatic conditions and the water supply of 

 southern Arizona follow. 



CLIMATIC CONDITIONS OF SOUTHERN ARIZONA. 



Precipitation. 



In the valleys the rainfall is usually so light that little of it 

 reaches the roots of orchard trees. The soil is seldom wet to a 

 depth of more than eight inches by one storm ; and usually the 

 rains are so infrequent that the soil becomes dried out between 

 storms. Hence, in growing fruits, orchardists rely wholly upon 

 irrigation, the supply for this purpose coming from the higher 

 elevations. 



In the mountains the precipitation is much greater, the fall 

 of rain and snow being sufficient during a part of most years to 

 cause a subsequent heavy flow in the streams that furnish water 

 for irrigation. A large part of the water that falls in the moun- 



