PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 1 DECEMBER 15, 1915 Number 12 
SALTS, SOIL-COLLOIDS, AND SOILS 
By L. T. Sharp ^ / 
COLLEGE OF AGRICULTURE. UNIVERSITY OF CALlI^RMAr^^ ^ " 
Presented to the Academy, November 1 , 1915 
To reclaim permanently and manage alkali lands successfully, or to 
use fertilizer salts with intelligence and profit, requires a consideration 
of the effects of these salts on the physical condition of soils. Not 
only must we bear in mind the effects of the salts while present in the 
soil, but also the condition that may result when these same salts are 
removed partially or wholly by natural or artificial drainage. In our 
experience in California this latter phase has proved to be a more 
difficult and perplexing problem than the former. The importance of 
this subject justifies the publication of this brief discussion, prior to the 
appearance of the detailed statement with reference to three years of 
work which we have carried out upon it. 
We know that, if a salt is added to a soil suspension, certain obvious 
effects are produced. Thus the common acids and their salts with the 
alkalies, the alkaline earths, and the heavy metals, as well as many other 
salts, flocculate suspensions in water of the soil mass. We associate 
this flocculated condition with an improvement in the working qualities 
of the soil. Another class of salts, those which give rise to an alkaline 
reaction, such as the alkaline hydrates, and as assumed, the alkah carbo- 
nates, possess within certain concentrations, the opposite power of 
deflocculating soil suspensions. Field soils so affected reflect this condi- 
tion by their imperviousness to water and their inferior cultivating 
qualities. 
Undoubtedly these phenomena are to be associated with the soil 
particles of such a fine state of division as to make their relatively 
large surface a factor of special importance. Possibly such particles 
may properly be designated colloids. Hence in attempting to explain 
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