1904 



FORESTRY AND IRRIGATION 



353 



two or three dollars per ton greater 

 concentrations may be allowed. 



The ordinary method of chemical 

 analysis of irrigation waters is certainly 

 greatly at fault, for an analysis usually 

 shows all the sodium carbonate and bi- 

 carbonate as sodium carbonate alone. 

 This is generally determined by evapo- 

 rating the water to dryness, which de- 

 composes the sodium bicarbonate and 

 leaves only the carbonate. Every 100 

 parts of sodium bicarbonate will by this 

 method give 62 parts sodium carbonate, 

 whereas, as has been shown, the reaction 

 within the soil is ordinarily in the oppo- 

 site direction, the tendency being tow r ard 

 the decrease of the sodium carbonate and 

 the corresponding increase of the bicar- 

 bonate. 



Of the white alkali salts, much larger 

 amounts are allowable in water. The 

 waters of the Pecos Valley in New Mex- 

 ico average over 300 parts of soluble 

 matter per 100,000 parts of water, and 

 where this water has been intelligently 

 used, the soils have remained fertile 

 after fifteen years of irrigation. This 

 water contains about 152 parts of salts, 

 easily soluble, and likely to accumulate 

 in the soil. In the Salt River Valley of 

 Arizona the waters of the Salt River 

 vary from 70 to 140 parts soluble matter 

 per 100,000, containing from 40 to 100 

 parts sodium chloride, and have been in 

 use for thirty years upon soils varying 

 from loose sands to heavy clay and 

 adobe, and w 7 here care has been exer- 

 cised in the use of such waters, no 

 trouble has been experienced frori the 

 rise of alkali. 



The waters of the Buckeye Canal, 

 taken from the Gila River about 20 

 miles below Phcenix, Arizona, carry 

 about 200 parts of soluble matter, of 

 which about 130 are sodium chloride. 

 This water is used upon light and, in 

 some cases, fairly heavy soils, and where 

 carefully handled has not resulted in the 

 accumulation of alkali in the soil. 



During the summer of 1902 it was the 

 writer's good fortune to visit some of 

 the oases of the Sahara Desert in eastern 

 Algeria. In these oases, artesian waters 

 carrying very large quantities of soluble 

 matter are successfully used for irriga- 

 tion purposes. Waters carrying as high 



as 8 10 parts per 100,000 parts of water 

 were used in growing vegetables, while 

 a number of wells carrying over 600 

 parts were in daily use, some of them 

 carrying over 300 parts of sodium chlo- 

 ride alone. This water was used for the 

 growing of fruit trees and vegetables, 

 many of which are grown in our own 

 country and are not considered especialty 

 resistant to alkali salt. 



These amounts of salt in irrigation 

 water are higher than those in common 

 use in America, and it should certainly 

 be encouraging to our engineers and 

 farmers who, in developing underground 

 water supplies, are constantly in dread 

 of damaging their land by alkali. 



Water containing 1,036 parts soluble 

 matter was found too strong for per- 

 manent irrigation in Algeria, although 

 there are places in Tripoli where sea 

 water containing 3,500 parts of soluble 

 matter is used occasionally for irrigat- 

 ing certain crops (date palms). 



It should be remembered that the 

 limit of endurance for most cultivated 

 plants, in a water solution, is about i 

 per cent, or 1,000 parts soluble matter 

 per 100,000 parts water, and if every 

 effort is made by the user of alkali 

 waters to keep the concentration of his 

 soil solution down to or below this limit 

 there need to be no fear from alkali. It 

 will be readily seen that every condition 

 which favors the concentration of the 

 w r ater in the soil cuts down the limit 

 allowable in the irrigation water, and, on 

 the other hand, every condition which 

 favors a ready flow of water through 

 the soil and a low evaporation of water 

 from the surface of the soil helps to- 

 ward making it possible to use alkali 

 waters in irrigation. To this end sev- 

 eral methods of procedure offer. 



It should be understood that the first 

 requisite of any land under irrigation is 

 good under-drainage. Where this is at- 

 tended to or naturally present, frequent 

 irrigation offers the simplest solution, 

 for by this means the soil solution is 

 kept dilute, and the excess of soluble 

 matter which would accumulate after 

 the evaporation of the water is washed 

 down into the subsoil and into the 

 drains. In Algeria, where the air and 

 soil are intensely warm (when visited 



