SOIL ANALYSIS. 
289 
In order to remedy this evil, the existence o£ which I suppose no 
one will be hardy enough to deny, various methods have been 
suggested and tried with the object of attacking the soil in a manner 
representing as nearly as possible the actual conditions which prevail 
in a field under cultivation. A few such reagents may be mentioned ; 
they include water saturated with carbonic acid, oxygenated water, 
acetic acid, citric acid, and different salts, such as ammonium citrate. 
In a recent series of researches Dr. Bernard Dyer* has experi- 
mented with a 1 per cent, solution of citric acid, which appears to 
approach closely, in its action upon the soil, the solvent power exerted 
by the acids secreted by the roots of certain plants. I venture to 
think that, notwithstanding the great scientific value of such a line of 
investigation, and of the light it may be expected to throw upon many 
obscure functions of plant-life, it leayes us pretty much where we 
were if we attempt to base upon its use auy practical advice to the 
farmer as to the nature of the manures or other treatment his soil 
requires. 
I am prepared to go a step further than M. Ville, and to say not 
only that we are unable to reproduce the agents at work within the 
soil in supplying the plant with food, but that we should gain very 
little from an economic point of view if we w r ere possessed of them. 
Bor, let us assume that the 4< universal solvent ” has been found, 
that we are possessed of a reagent which exercises the same solvent 
action on the soil as, let us say, a wheat crop ; in other words, one that 
dissolves from the soil the same amount of mineral and nitrogenous 
matter as the wheat crop will extract during the period of its growth. 
We are met with the following difficulties : — 
Our wheat crop, though it contains less nitrogen (say, one-third 
less) than a crop of turnips, will nevertheless benefit very much more 
than the latter by an application of nitrogenous manure ; that is to 
say, the wheat crop cannot make the same use of the nitrogen in the 
soil as the turnip does — exercises, in fact, a different solvent action 
upon the nitrogenous constituents. 
Or, since the nitrogen in the soil is continually changing its 
condition, and there are external sources of nitrogen which may have 
some bearing in the above instance, we may take a case which is even 
less ambiguous. 
The mangel crop removes from the soil nearly double as much 
phosphoric acid as the turnip crop does ; nevertheless, manuring with 
superphosphate is of less benefit in the case of mangels than with 
turnips, the recognised reason being that mangels are able to utilise 
the phosphoric acid, as it exists in the soil, to a greater extent than 
turnips. So that it will be necessary for us to devise one solvent for 
turnips and another for mangels, one for phosphoric acid and one for 
potash — a separate set of solvents for every crop ; and such a scheme, if 
it were feasible, would be far too cumbersome for practical purposes. 
A second objection lies in the fact that the agencies at work 
within the soil are unceasing, and, as a consequence, the combinations 
in which the nitrogen and the mineral matter exist are also constantly 
changing. What is true of the chemical constitution of the soil 
to-day is no guide as to its constitution a week hence. 
* J ournal of the Chemical Society, March, 1894, 
T 
