General Discussion 221 



addition of copper to new ground that may occur through irri- 

 gating waters, it is not impossible that in favorable situations an 

 actual increase in vegetable growth in the field due to copper 

 may take place ; but it is not possible in the field to prove this 

 supposition because of many other factors, the effects of which 

 prevent trustworthy observation. 



Field Observations 



In view of the many factors influencing results in the field, 

 some leading towards toxic copper effects, some opposing toxic 

 effects, and still others pointing to the possibility of stimulated 

 growth, it is of interest, finally, to refer to field conditions as 

 they have existed in irrigated lands under the Clifton-Morenci 

 mines for the twelve years during which the district has been 

 under observation. At the beginning of this period, in 1904, 

 considerable accumulations of copper-bearing tailings were evi- 

 dent, more particularly at the heads of alfalfa fields, where they 

 sometimes attained a thickness of as much as ten inches or more. 

 These blankets usually thinned out and disappeared between 100 

 and 200 feet from the head ditches, leaving crops in lower por- 

 tions unaffected. Deposits of river sediments were observed in 

 other irrigated districts not affected by mining detritus. The 

 growth of alfalfa was more depreciated by the denser and thicker 

 tailings blankets ; and yellow foliage of young grain and young 

 corn was considerably in evidence in tailings, but not as an effect 

 of ordinary sediments. In 1908, the tailings were impounded, 

 and some of the best farmers began the practice of cultivating 

 alfalfa to break up the old accumulations, incorporate them with 

 the soil, and secure better penetration of water and air to the 

 roots of the crop. Following this procedure the stunted growth 

 at the heads of alfalfa lands has considerably but not yet en- 

 tirely recovered. Patches of yellow young barley, wheat, and 

 oats are still to be observed on old tailings deposits ; but as the 

 plants become older they become normal in appearance, and 

 yield apparently normal crops. These observations, which may 

 be repeated many times in the course of a day's reconnaissance 

 in the district, from May to September for alfalfa, and February 



