140 THE MONTHLY BULLETIN. 



THE APPLICATION OF WATER TO CITRUS ORCHARDS 



AND THE MAINTENANCE OF THE PROPER 



MOISTURE CONTENT OF THE SOIL. 



By V/. M. Mertz, Superintendent of Cultivations, Citrus Experiment Station, 



Riverside, California. 



Irrigation is absolutely necessary to successful citrus culture in Cali- 

 fornia. Without the supplementing of our scant winter rainfall with 

 applications of stored water during the dry summer months such a 

 thing as a citrus orchard would be unknown in the southwest. 



The annual rainfall for most of our citrus districts rarely exceeds 

 15 inches; practically all of this falls during the winter months. Thus 

 it is obvious that some water must be artificially applied to the soil 

 during dry, hot summer months. 



Various' methods of application have been used by citrus growers 

 since the industry began. One of the first methods was the basin 

 system which applied the water in ponds about the trees. These basins 

 vvere connected and thus several rows of such basins could be kept 

 filled at one time. This scheme, however, was largely abandoned as 

 the orchards grew older and various troubles arose, which were traced 

 to the standing water about the trunks of the trees. 



With the discovery of the ill effects following the repeated soaking 

 of the soil about the base of the trees this system was modified to over- 

 come these troubles. Ridges similar to those used in the former system 

 were made, but the basins in this case occupied the areas between the 

 trees instead of the land al)Out the tree itself. Thus the soil shaded 

 by the tree was not flooded and the troubles resulting from the earlier 

 method were largely corrected. However, it was found that except on 

 very sandy soil deep penetration of the water was almost impossible 

 with this system. The covering of the entire surface of the soil with 

 a blanket of water prevented the free outflow of the air occupying the 

 spaces between the particles of soil and after the surface soil was 

 thoroughly wet the water entered the lower stratas very slowly. This 

 fact gradually became known and during this time the plantings of 

 citrus had gradually crept up the sides of the foothills where such 

 flooding methods were impracticable. 



These two facts led to the general adoption of the furrow system 

 of irrigation, which is now almost universally used in the citrus 

 orchards. 



In discussing the application of water to our citrus orchards I shall 

 deal only with this furrow method. 



There are several variations to this practice. For instance, some 

 growers run the furrows very close together; others five or six feet 

 apart. Some make deep furrows, while others make them shallow. 

 Some zigzag the furrows in and about the trees. Others check the 

 furrow, as it is called, when water is run back and forth between two 

 furrows, thus checking the flow of the water when the grade is heavy. 

 Again, some irrigate with furrows 800 to 1,000 feet long, while their 

 neighbors may use furrows only 200 or 300 feet in length. 



Taking up first the question as to the proper spacing of the furrows, 

 no set rule can possibly be given, as the distance should vary with 



