952 PROCEEDINGS OF SECTION G. 
But, in addition to these salts, special consideration must also 
be given to the chlorides, which have not only the deterrent 
effect common to all salts—which, in dry seasons, form concen- 
trated solutions in the soil, and thus interfere with osmotic action 
of the root hairs,—but have also a specially poisonous action, to 
which many plants are very sensitive. Let us assume that any 
chloride above 30 may, in a dry season, be accounted injurious. 
As the surface soil of plot 7 contained 50 of chlorine, there was 
on this basis an excess of 20. Let this 20 be added to the 21 
representing the soluble salts, as indicated by the excess of 
potash ; we then get the figures 12, 41, 2, 18 as representing the 
deterrent effect of the soluble salts in the four plots respectively. 
Subtract these from the figures already obtained for the effect 
of the nitrogen, phosphoric acid, and lime, and we get the 
following :— 
1,096 1,046 1On9 881 
as representing the total effect of the constituents disclosed by 
the analysis. These are represented in the diagram by the bottom 
curve but one—the dash lines. It will be seen now that even in 
detail the curve closely agrees with the curve representing the 
actual productiveness. 
Briefly stated, it appears, from a consideration of these facts, 
that in considering the agricultural value of these soils, as disclosed 
in the results of a chemical analysis, that the chief weight is to 
be assigned to the phosphoric acid, in accordance with Liebig’s 
law of minimum, that the nitrogen must receive the next con- 
sideration. Minor consideration must then be given to the 
favourable mechanical effect of the lime in the soil, and to the 
injurious effect of excess of soluble salts, notably of chlorides. 
In conclusion, I wish to point out that this short paper is 
submitted merely as suggestive. The short series of facts on 
which it is based are not a sufficient foundation for any general 
conclusions ; nor, indeed, are they in themselves of sufficient 
importance to justify the rather elaborate treatment to which 
they have been subjected. The elaboration has been undertaken 
merely to indicate what, in my opinion, is in general the proper 
attitude of mind to assume when considering the results of the 
chemical analysis of soils. 
