POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 25 
Acid soluble — Continued. 
CaO 12. 6 
NaX>+K 2 3.2 
Po0 5 1.0 
S0 3 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), and 
the average amount for soils of humid areas somewhat less than 1,000 pounds per 
acre-foot (0.03 per cent). Hilgard 2 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. 3 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, as 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 
i 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. 
