58 
IOWA ACADEMY OE SCIENCES. 
CHEMICAL ANALYSIS OF SOILS. 
BY G. E. PATRICK. 
There is hardly a subject upon which the opinions of chemists 
differ more widely than upon that of the utility of soil analysis, 
as a means of judging of the present crop-producing power of 
soils, or of ascertaining in what particular element or elements 
their store of available plant- food most needs replenishing in 
order to restore or increase fertility. This difference of opinion is 
not because any one questions the efficiency of chemical analysis in 
determining the total amount of the several plant-food elements 
present in the soil. That is easily done. The difficulty lies in 
determining how much of this total amount is in such condition, 
or combination, as to be readily available to the growing jDlant. 
This the chemist is as yet unable to do with certainty. 
It is not my intention to imply that there is a hard and fast 
line separating these two groups, the available and the unavail- 
able plant-food materials of the soil; for as regards the mineral 
matters, at least, availability is a matter of degree; and more- 
over, certain stores of plant-food, in one and the same soil, 
seem more available to the one class of plants than to another. 
Nevertheless the distinction, as ordinarily made, is entirely 
valid; the debatable ground is narrow; on one side of it are the 
compounds readily soluble in the root juices of all plants — the 
distinctly available; on the other side are the great stores of 
food material in forms nearly insoluble in the root- sap of all 
the higher plants — the unavailable. 
Evidently some means of distinguishing between these two 
groups is much to be desired, to enable the chemist to ascer- 
tain with certainty the needs of any particular soil in respect 
to readily available plant-food; and the hope of finding such a 
means has been the motive of a number of researches in recent 
years. 
The solvent that for many years has been employed for 
extracting the soluble portions of soils, is hydrochloric acid. 
