POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 25 



Acid sohible — Continued. 



CaO 12.6 



NaaO+KjO 3.2 



P2O5 1.0 



SO3 8 



Total acid soluble: 



Arid (per cent) 29.5 



Humid (per cent) 16. 



These ratios indicate a much greater proportion of soluble material on the whole 

 in the arid than in the humid soils. The greater proportion of soluble silica and acid 

 soluble alumina would indicate more favorable conditions for the absorption of alkalies 

 in the case of arid soils. The greater proportion of alkalies and alkaline earths indi- 

 cates that absorption either by chemical reaction or by simple retention of soluble 

 salts is a marked feature of arid soils. 



While absorption by chemical reaction is of undoubted importance, absorption 

 by retention of soluble salts is of much greater importance and is characteristic 

 of the soils of the basin region. Whitney and Means state ^ that the soluble salts 

 for soils of a sandy nature approximate 50 pounds per acre-foot (0.0015 per cent), 

 for heavy soils from 3,000 to 4,000 pounds per acre-foot (0.09 to 0.12 per cent), ajid 

 the average amount for soils of humid areas somewhat less than 1,000 pounds per 

 acre-foot (0.03 per cent). Hilgard ^ states that very few of the upland soils in the 

 arid regions of California contain less than 2,000 to 2,500 pounds of soluble salt per 

 acre in the first 4 feet. In the soils of the lowlands the content of soluble salt must 

 be considerably greater. No general numerical statement can be made for the soils 

 of the basin region, but we know that in many cases the amount of soluble salts 

 must be many times greater than that contained in the soils of humid regions. Table 

 XIV (Appendix) gives the content and chemical composition of the soluble salts for 

 a number of soils in the basin region. I have taken most of these from three widely 

 separated localities. The first set are from soils in the vicinity of Fallon, Nev.; the 

 second from soils in the vicinity of Salt Lake, Utah; and the third from southern 

 Oregon. The average content of soluble salts for the Fallon soils is 1.23 per cent and 

 for the Utah soils 1.8 per cent. It should be noted that the examples given are un- 

 doubtedly from localities more or less heavily impregnated with soluble salts. The 

 average for the Fallon area can be obtained from figures presented in the advance 

 sheets of the field operations of the Bureau of Soils, 1909.^ The content of alkali 

 and the acres affected in each instance are given: 



82,624 acres contain less than 0.2 per cent alkali. 

 38,784 acres contain from 0.2 to 0.4 per cent alkali. 



8,768 acres contain from 0.4 to 0.6 per cent alkali. 



8,128 acres contain from 0.6 to 1.0 per cent alkali. 

 12,096 acres contain over 1 per cent. The average content for 150,400 

 acres is 0.4 per cent. 



While the results for the Fallon section can not be taken as representative of the 

 basin region, still it can be said that they show the results for one important area. 

 The conditions in other portions of the basin, and particularly south of the Fallon area, 

 can not be much different. In fact, ae we proceed south the evidences of soluble 

 salts become more and more common. Many of the flat valleys which characterize 

 southern and central Nevada show that the conditions are very favorable for the 

 retention of the soluble salts. The physical conditions influencing the retention of 

 salts by and their movement in soils merit some discussion and the succeeding section 

 covers this subject. 



RETENTION AND MOVEMENT OF SOLUBLE SALTS BY SOILS OF ARID REGIONS. 



The factors controlling the retention of soluble salts are underground drainage, 

 character of the soil, slope of soil surface, and rainfall. With good underground 

 drainage, even under arid conditions, there is a gradual movement downward of the 

 soluble salts. Underground drainage is dependent upon the character of the soil and 

 the slope of the soil surface. With compact, heavy soils much seepage water is retained 

 and drains away very slowly, or not at all. Capillarity acts in fine-textured soils to 

 return the ground water, in some cases back to the surface, or in others to some interme- 

 diate level. With porous, open, and coarse-textured soils capillarity may act to a small 



1 Bui. No. 14, Bureau of Soils, p. 22. 



2 Bui. No. 35, Bureau of Soils, p. 13. 



3 Soil Survey of the Fallon Area, Nevada, p. 43. 



