EB. W. Hilgard— Objects and Interpretation of Soil Analyses. 183 
ArT. XXXI—The ac and Interpretation of Soil Analyses ; 
by E. W. Hitearp, Professor of Agriculture at the Minh 
versity of California 
THE claim of soil analysis to practical utility has always 
been rested on the general supposition that, “ other things being 
equal,— produ tiveness is, or should be, sensibly proportional to the 
amount of available plant Jood within reach of the roots during the 
period of the plants’ development ;” provided, of course, that suc 
supply does not exceed the maximum of that which the plant 
can utilize, when the surplus simply remains inert. 
The above statement has been, either tacitly or expressly, 
in the development of agricultural science, and of rational 
agriculture itself. Its acceptance is implied in the search for 
the solvent that shall represent correctly the action of the plant 
itself on the soil ingredients ; and I shall take it for granted in 
this discussion, while strongly van the proviso, espe- 
cially with reference to physical condition 
Methods of Sovl investigation.—It is universally admitted that 
the ultimate analysis of soils affords little or no clew to their 
agricultural value; such agents as fucloneby acid and alkaline 
carbonates go by far deeper than the solvents, naturally acting 
in soils bearing vegetation, will go within the ‘limits of time in 
which we are interested. 
Many attempts have been made to find solvents whose action 
the needs of vegetation, that eee en as to the present 
agricultural value of a given soil could be deduced therefrom. 
tis needless to recite the long list of such solvents, suggested 
since nt analysis attracted attention. From fluohydric acid 
to water charged with carbonic acid, the acid solvents have all 
signally failed to secure even an approximation to the result 
desired, viz: a consistent agreement between the quantitative 
determinations, or the percentages of plant food, found in the 
tories soils, and the actual experience of those who cultivate 
the 
It has been attempted by the German experiment stations, 
under Wolff's initiative, to gain an approximation to the rela- 
tive availability of parts of the soils’ store of plant food, by 
consecutive extractions with acid solvents of different strength, 
Ros rw: with distilled water and ending with boiling oil of 
Am. Jour. rie Pisses Series, VoL. XXII, No. 129.—SePTEMBER, 1881, 
