286 THE FUTURE OF ARID LANDS 
ABERSS 
Sodium and Chloride for Seven Stations on the Rio Grande above Fort Quitman, Texas 
(Annual means and totals for the year 1949) 
Sodium Chloride 
Station 
ppm meq/! tons ppm meg/l tons 
Otowo Bridge, New Mex. WG) O84 4, 70m PGW 13,3018 
San Marcial, New Mex. AE TOR OE 25 24 1) 45 CS 
Elephant Butte, New Mex. Be Dacl9) OU OHO air Sy) | Gyan UO 
Caballo Dam, New Mex. GH DAR COSAos PV 1b OYA ZB ex) 
Leasburg Dam, New Mex. TOUS LOMMO Opp G2 Aye OR OAS 
FE! Paso, Texas 147 6.41 92,940 ONS TS BoB SSC 
Fort Quitman, Texas 601 26.15 109,546 874 24.65 159,298 
@ From same sources as Table 2. 
has been a large reduction in the amounts of sulfates and bicar- 
bonates. 
On the basis of the data for discharge, salt burden, salt concen- 
tration, and composition of Rio Grande waters, it is clear that 
the quality of irrigation water downstream may be affected 
adversely where there are diversions for irrigation that deplete 
the flow. The data also indicate the importance of an accurate 
knowledge of the quality of water if it is to be used for irrigation. 
Use of Saline Waters for Irrigation 
With accurate data on quality at hand, the next consideration 
is: can waters of low quality be used without inducing unde- 
sirable effects on the properties of the soil to which they are 
applied and the crops which are to be grown? 
If waters of high salinity are used for irrigation without proper 
management or adequate drainage, the salts accumulate in the 
root zone and the concentration of the soil solution increases. 
As the salt concentration or osmotic pressure is built up, there is 
a decrease in the ability of the plant roots to absorb water in 
adequate quantities. Experimental work has shown that retarda- 
tion of plant growth is virtually linear with an increase in osmotic 
pressure of the soil solution and, in most cases, it is largely 
independent of the kinds of salt present. When the osmotic 
pressure of the substrate has increased sufficiently, the entry of 
water into roots will cease, and most crop plants will die. 
