94 Bulletin No. 34. 



lows of its removal. But the worst effect is its corrosive action 

 directly upon the plant at or near the surface of the ground where, 

 especially in hot, dry weather after an irrigation, the alkali, as an 

 effect of evaporation, collects in the form of a crust. 



In Salt River Valley the average of twenty analyses shows 

 only .044 per cent of black alkali, but at some of the lower levels 

 where the ground is subirrigated by water from the canals, black 

 alkali exists in destructive amounts, having been concentrated 

 through the action of irrigating water. 



The seepage from such localities carries black alkali in solu-, 

 tion, as is the case in Jenkin's seepage ditch near Double Buttes, 

 southwest of Tempe. On the other hand, Salt River has been ob- 

 served to contain lime in the form of gypsum, which is an anti- 

 dote for black alkali. At a time of high water this upper-river 

 water may modify or overcome the alkaline character of seepage 

 water. It is therefore probable that lands lying under seepage 

 canals are at some times benefitted, apart from the addition of silt, 

 by the application of upper-river water. 



The best remedy for alkaline salts of any sort, where drain- 

 age is possible, is to flood the ground for a sufficient time, many 

 days if necessary, to carry the salts down and entirely away into 

 the country drainage. This is practiced in Utah and is stated to 

 have been done near Buckeye. 



In small areas of valuable lands, g}'psum, in a well drained 

 soil, can sometimes be used with economy to overcome black alkali. 

 One ton per acre of gypsum would overcome about .036 per cent 

 of black alkali in the surface foot of soil. Gypsum exists near 

 Vail's station, twenty miles east of Tucson, and the chief cost 

 would be that of transportation. 



Much land is being cleared at this time of year in preparation 

 for planting, the brush often being collected in great piles and 

 burned. Since ashes contain black alkali in considerable amount, 

 the site of an old brush fire may easily be marked by an alkaline 

 spot in years to come. It would be better to drag the brush to 

 the roadside where possible, or burn it in very small piles so as to 

 distribute the alkaline ashes. 



Ashes, also, are sometimes used here as a fertilizer. In Eas- 

 tern states, where the rainfall prevents the accumulation of alkali 



