DRAINAGE OF IRRIGATED SHALE LAND. 9 
TABLE II.—Analyses of seepage waters through virgin shales. 
(No land lying above ever under cultivation.) 
Milligrams per liter (parts per 
oy I 
Substance. 1915, 1915, 1916, 
Nov. 18. | Nov. 12..| Apr. 29. 
A B. C 
Ions 
Sulphuric acid (SO4)....-.-------- SPE N Ns ash DS Mp pe RE A LILY ae 4, 236 21, 800 37,612 
(Chin ooite a¥er(G) (COB) s sas adub dasanc so sed abs Gus BuoueNaE Sesh eendnecboose eos socosor cas 96 77 
Bileeir lovee Yoo! (AB KOO RAEN Ce Bi Rapes lee Meee Maen a el aoeuens 434 849 710 
INIT ENO EK OIG (NKOSI Sees et eas aa ie as ae eS ee ere Ree, ere A ee Ue 4,004 577 1, 687 
CON al operas (CA ats oe ee eT A UL a See eee een yay Ne Ae ar i 480 1, 038 2, 783 
Opi Vernon aat (Opes) ees of SN SO OS e eae est Sta ee a Cae Tue, Bry NNN Lc Serres 1,110 567 535 
Niaomecibiiny (VIG) veel smesser sine ra teat Sie leh cide Nee Se ee sete aa 523 2,481 2, 556 
Sodimm\@Nia) pees see ese he Sete coe Reape i el re OTE) a Be Ue NP He 1,725 6,376 15,318 
PROSENSE SA GIS SRR ane Ne Wea Ne sat eR a ME aE Nel 12,512 | 33,784 61, 278 
Hypothetical combinations. 
S@chivnan Ganlooienie (GNEIOOM ce aneecsedesosesee se seceeseosenosecceesdaued so [sar oeenen 170 136 
Macmesiumr chloride GM el) secs nn cits mFS AES Se bees gute Nay Ouse Uel oe fe WAS 5| Beare a ein aay aml aeie 
Mayes IAN SUOMI) GUIISION). 5 Scab oc oss ssagecenenasdossdsasuondossouue 2,402 12, 282 12, 653 
Soaiumbmiitna rey GNGIN@ se ws he a ee ee ic es ee estes 5, 489 791 2,313 
Sociumrra ell Ori dey GN GI) ae ae ena ie 2 el a pepo feaiente SEs 609 gala 4,588 
Socliwrm soho GNeyIOMW) 5 Seeks es soodseceecocsssnaesbonossooaueenabelscooscosoe 16, 723 39, 620 
Calciummsulphate (CaS Os) ie: sae eecia en- are lola sept e es ea clere merece =r 3, 287 979 1, 025 
Calciumuebicarbonater(CaG@HiCO3s)s) aoe een eee Ee ee eee eee ees oe 577 1,128 943 
Calciumercarbomate: (CaS O's) ke ee NEN aa 8 BN ie eases oa 
These are all bad waters, as only three of the 13 samples show less 
than 10,000 parts per million, or 1 per cent, of the soluble salts, and 
one of these is but slightly below this figure. The average for the 13 
samples is slightly in excess of 23,700 parts per million, or 2.37 per 
cent. 
An acre-foot of water weighs 2,722,500 pounds and with a salt 
content of 23,700 parts per million will contain 64,523 pounds of 
salt. Assuming the weight of an acre-foot of soil at 4,000,000 pounds, 
the salt that would be left in the soil by evaporation from it of but a 
single acre-foot of this water would be equivalent by weight to 1.6 per 
cent for the top foot of the soil. .If this quantity were distributed 
throughout a depth of 4 feet, it would mean an average of four-tenths 
of 1 per cent. It is conservative to assume an annual evaporation of 
36 inches under such climatic conditions as exist in those sections of 
the United States to which this bulletin refers, so that it would re- 
quire but one season to deposit enough salts, by evaporating the aver- 
age of the waters represented by Tables I and II, to make the situa- 
tion three times as bad as the above. Allow surface evaporation, re- 
sulting from poor drainage, to continue for a number of years and 
the situation with respect to alkali is rendered extremely serious. 
Many investigators, working independently, have attempted to 
establish a comparative standard relative to the tolerance of plants 
for the different alkali salts present in a soil. Owing to the variety 
70250°—Bull. 502—17——2 
