IRRIGATION SUGGESTIONS 189 



Weir Measurement. The term "weir" is not always understood 

 by those who use it. The term can properly be used only for struc- 

 tures designed to allow the water to flow over the crest with a con- 

 siderable fall on the down-stream side. There are a large number of 

 forms of weirs, taking their names from the shape of the weir notch, 

 or the form of crest. The triangular weir has a V-shaped notch. 

 The rectangular weir has a horizontal crest with vertical sides. Both 

 of these forms of weir are good, when used by the expert irrigator 

 or engineer who understands the principles and factors which enter 

 into their calculations. Water measurement as practiced by irriga- 

 tion companies is, however, rather more a question of engineering 

 than of fruit growing and cannot be pursued in this connection. 

 Several publications on the subject are readily available.* 



DANGER OF ALKALI IN IRRIGATION WATER 



Every since Prof. Hilgard's original observations on alkali were 

 published, Californians have been aware of the danger of using 

 waters containing alkali for irrigation purposes, but they have not 

 realized, until recently, of how much significance this is. Investiga- 

 tions and observations made by the California Agricultural Experi- 

 ment Station show that many of the well waters used for irrigation 

 purposes in orchards contain so much alkali, usually including 

 common salt, that though beginning with a soil free from alkali, one 

 can readily impregnate it with salts enough in a few years to ruin 

 an orchard. The investigations emphasize further some general 

 alkali problems in orchards, even where fairly good waters have 

 been used, and render the alkali question one of the most important 

 in soil management problems in arid parts of California. The fruit 

 planter should never plan to use water from any source for irriga- 

 tion without having proper samples analyzed and the analysis inter- 

 preted.f River and stream waters are usually found to be purer 

 and better than well waters in the citrus districts, in which the 

 investigations cited were carried out. Nevertheless, recourse to 

 analysis is always a safe guide. 



RANDOM SUGGESTIONS 



Without attempting an impossible thing, to-wit, to furnish ex- 

 plicit directions for the practice of irrigation, for much of it every 

 man must learn for himself by experience, a few suggestions may 

 be noted. 



Usually water should be prevented from actual contact with the 

 trunk of the tree. Citrus trees are especially sensitive to such con- 

 tact, and resent it by "gum disease," which was formerly far more 



'Bulletin 247 of the California Experiment Station on "Some Measuring Devices Used 

 in the Delivery of Irrigation Water" (Jan., 1915): "Farmers' " Bulletin 813. U. S Dent 

 Agr., on "Construction and Use of Farm Weirs" (June, 1917): Circular 36. Utah Experi- 

 ment Station, Logan, Utah, on "Practical Information on the Measurement of Irrigation 

 Water" (January, 1919). 



fThe ill effects of irrigating with alkaline water are strikingly set forth by W. P. Kelly 

 and E, E. Thomas ki Bulletin 318 and Circular 219 of the University of California, Berkeley 



