IO BULLETIN 83. 
this case were calcic, magnesic and sodic sulfates principally. The 
distribution of salts in *the soil has an important bearing upon this 
question. These observations were not the results of prearranged 
experiments but indicate just as certainly as though they were, 
that large quantities of these salts may be present in the soils, 
other conditions being favorable, without precluding successful 
cropping. 
If these figures be nearly correct, we can have in the first foot 
of soil as much as 25 tons, but probably not more than 50 tons of 
these salts, the mechanical condition of the soil and the drainage 
being good, before the salts become decidedly injurious. Accept¬ 
ing this maximum which is tentatively given as approximately 
correct, and based upon a limited experience, we may get a clearer 
view of the importance of this question. Taking a water as rich 
in mineral matter as Terry lake water, carrying three tons of salts 
in each acre-foot, we see that the application of nine acre-feet 
would add an amount of salts in excess of our lower limit. These 
salts would have been applied at the surface of the soil in nine 
successive portions, and unless it were carried down into the soil 
with the water, would already appear as an incrustation, especial¬ 
ly under favorable weather conditions. 
There is no doubt but that the soil does, as it were, strain 
out some of these salts, but it takes a thick layer to accomplish 
this. It would be difficult to explain how this is done but the 
soil particles hold on to these salts in some way and do not 
permit all of them to pass through the soil with perfect freedom. 
Indeed it is not probable that it permits any of them to pass 
through with perfect freedom but it retards some more than it 
does others. These salts are not collected within the first foot of 
soil, nor within the second, but may pass down several feet before 
they are stopped, so that, while there may be an addition of these 
salts held in solution in the water, as there evidently is, the ad¬ 
dition is not necessarily to the surface soil, though the water is 
applied there. There is another thing that helps us in this case. 
The soil selects the salts which it retains and it seems to permit 
the most dangerous ones to pass through it more readily than 
some others. The ratios of the salts in solution in the water as it 
is put onto the ground, while it is in the ground, and as it flows 
out of the ground, are not the same. We cannot attempt to dis¬ 
cuss this subject. The following statement is by no means per¬ 
fectly accurate but it will serve roughly to show how the sodic 
carbonate, for instance, is permitted to pass through the soil more 
readily than the sulfate. 
In an experiment which we made we found that an acre-foot 
of irrigation water contained 438 pounds of sodic carbonate, the 
water in the soil at a depth of from two to four feet contained 543 
