1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 443 



served to contain much less copper than other grain roots grown 

 in similar soils, a fact to be attributed to the coarse character 

 of field samples of corn roots. 



USE OF COPPER SULPHATE TO KILL MOSS IN 

 IRRIGATING DITCHES 



Clear irrigating water supplies, such as are derived from 

 seepage and from wells, quickly become choked with mosses and 

 algae in warm weather, entailing loss of water and expensive 

 ditch cleaning. In order to test the application of copper to 

 a running stream for the purpose of killing the growth of 

 aquatic plants, an experiment was conducted, in October, 1906, 

 upon the Flowing Wells ditch near Tucson, which at the time 

 contained abundant aquatic growth. 



A barrel of copper sulphate solution was prepared and placed 

 at the head of the ditch. By means of a small outlet controlled 

 by a stopcock, fifteen pounds per hour of CUSO4.5H0O were 

 added to the ditch flow, this amount being in the proportion of 

 1 part of copper to 100,000 of water. Most of the copper was 

 immediately precipitated by the bicarbonate of lime present in 

 the water ; still more probably combined in insoluble form with 

 the soil along the ditch; while the remainder acted with toxic 

 effect upon the sensitive algae and the less sensitive mosses 

 (Potomogetons) growing in the water. A short distance below 

 the barrel, where algae and mosses, after twenty-five hours' ex- 

 posure to copper, were brown and dead and breaking away from 

 their points of attachment, .84 parts of copper in 1,000,000 of 

 water remained in solution. Three miles below the barrel, where 

 the mosses and algae were still plainly affected, traces only of 

 dissolved copper were perceptible. A renewal of copper from 

 point to point would therefore have been necessary in treating 

 a long ditch by this method, which, however, proved too costly 

 for adoption in the instance mentioned.'^ 



It is of interest in this connection to note that in the early 

 days of irrigation on the Gila River, mosses grew in such abund- 

 ance in the clearer waters obtained from the river at that time. 



7 See Bibliography, p. 488, reference 32. 



