SOIL SURVEY OF SOLOMONSYILLE AREA, ARIZONA. 25 



of the area containing- from 0.20 to 0.40 per cent most of the alkali 

 exists in the lower part of the 6-foot section. Alfalfa, when once 

 started, makes nearly a normal growth on these areas, and in some 

 cases does well. In soils in which the salt content does not exceed 

 0.40 per cent, sugar beets, sorghum, and alfalfa may be grown with 

 profit; provided precautions are taken in starting the crop. Often a 

 moderately heavy irrigation before seeding will result in the move- 

 ment of the surface salts toward the subsoil. By the time they return 

 to the surface the crop may have sufficient stand and vitality to endure 

 the injurious effects of the salts. Even slight alkali accumulations, 

 however, are alwa\\s a source of danger, and soils in which they exist 

 should be carefully handled. 



Sodium chloride, or common table salt, is of common occurrence in 

 the Gila Valley area and forms a large proportion of the alkali salts 

 of the region, both in the soils and in the underground waters. While 

 less harmful in its effect upon plant growth than some of the other 

 salts, it is in abnormal quantities a dangerous substance. 



Sodium sulphate also occurs here in large amounts, and with sodium 

 chloride forms by far the greater proportion of the total alkali salts 

 of the area. Upon the surface it sometimes appears as a white, pow- 

 dery crust, readily blown into the air, and has an irritating effect upon 

 the mucous membrane of the throat and nasal passages. 



These two salts form practically all the ""white alkali" of this area, 

 the sulphates, chlorides, and phosphates of calcium, potassium, and 

 sodium, respectively, occurring in small amounts. 



Bicarbonate and carbonate of sodium are also common alkali salts, 

 appearing to some extent in the Gila Valley area. The former is 

 classed with the less harmful of the alkali salts. It may, however, by 

 giving rise to the sodium carbonate, be indirectly capable of doing- 

 great injury. 



Sodium carbonate, or "black alkali." as it is commonly called, is 

 one of the most dangerous salts. It is, strictly speaking, an "alkali," 

 corroding and destroying both the humus or vegetable matter of the 

 soil and the tissues of growing plants. In its effects it is several times 

 more deadly than either the chloride, sulphate, or bicarbonate of sodium. 

 Its action in corroding and dissolving the organic matter of the soil 

 imparts to the moist soil surface, and to pools of seepage water where 

 it is concentrated, an inky black color. Although sodium carbonate 

 is frequently detected both in the soil and water of the area, it occurs 

 in large or dangerous quantities only in a few spots, too small to be 

 shown on the map, where the total salt content is greatest. Sodium 

 carbonate may, in poorly drained areas, be formed by the evaporation 

 of bicarbonate solutions from the surface, carbon dioxide being slowly 

 given off and the salt remaining in the less carbonated form, or as 



