1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 459 



salts were percolated through one to twelve inches of soils, with 

 little or no copper appearing in the filtrates. Under field con- 

 ditions, therefore, this action tends to concentrate dissolved 

 copper in irrigating water in the surface few inches of the soil. 

 A series of samples of Montezvima Canal water taken at 

 Solomonville affords quantitative suggestions in this connection : 



TABLE XXIX 



Copper Content of Gila Eiver Waters 



Amounts of Cu added 



in irrigation, estimated 



in p. p.m. of water 



Description 



Sample No. and 

 date 



3309 May 26, '04 River very low 18.3 

 3486 June 11, '05 Small flood 



In In 



tailings solution Total 



.80 19.1 



9^ 



3622 June 25, '06 

 3737 Feb. 22, '07 

 4011 Jan. 3, '08 



River low 

 Medium flood 



1.6 .11 1.71 



trace 2.88 ±3.0 

 2.1 .08 2.18 



Approx. 



flow of 



Gila 



River 



in sec. 

 ft. 



30 

 170 



600 



Approx. 

 amts. of 



copper 

 carried 



down 

 stream, 



1 dav 

 lb. 



3094 



230 



(Soluble 

 only ) 



9720 



Tailings shut out of river May 1, 1908 



4029 Apr. 12, '09 

 6342 Mar. 4, '16* 



1.4 

 .04 



.08 

 .03 



1.48 

 .07 



* Following four-months shut-down of operations in Clifton-Morenci 

 district. 



These figures, while somewhat meagre, seem to indicate a 

 lessening waste of copper downstream following the restraint of 

 tailings from the water-supply in May, 1908. This is especially 

 true of copper in solution, due probably to the decreased amounts 

 of solid copper compounds in suspension from which copper in 

 solution is derived. 



Assuming at the present time an average of 1 part of copper 

 in 1,000,000 of Gila River water, four acre-feet of such water, 

 required for one year's irrigation, would contain 10.9 pounds 

 of copper, from which should be deducted small losses due to 

 vegetation, drainage waters, and percolation to depths below the 

 surface soil. 



Six tons of alfalfa with a copper content of 5 p.p.m. contain 

 0.06 lb. copper; while one acre-foot of seepage water (about the 

 annual seepage loss) containing 0.25 p.p.m. copper would carry 

 0.68 lb. copper. Estimating the total loss roughly at one pound 



