September28, less.] JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
299 
Since the days of Liebig, however, the researches of Ville, Lawes, 
and Gilbert and others, have shown that the deficiencies in soils 
brought about by ordinary agricultural practice may be confined 
to three or four of its food constituents—viz., nitrogen, phosphoric 
acid, potash, and lime. The amount of these constituents 
present might therefore be said to govern the fertility of the soil, 
providing they exist in an available condition, and the physical 
characteristics of the soil are such as to allow of their favourable 
action. A liberal use of farmyard manure tends to keep a fertile 
soil in its normal condition, prevents its exhaustion, and in many 
cases even improves it; but unfortunately the supply of this 
general manure is insufficient for the purpose, ard recourse has to 
be made to more concentrated forms of the individual food con¬ 
stituents. Nitrogenous manures for gramineous crops, phosphatic 
manures for root crops, and potassic manures for leguminous 
crops, are those which produce the best results. These have been 
termed special manures, and their use is attended with consider¬ 
able economy, since their application to the crops specially re¬ 
quiring them gives the best results with the least expenditure. It 
is necessary, however, that all other food constituents should be 
present in sufficient quantity, since, as Liebig states, the fertility 
is governed by the constituents present in minimum quantitj-. 
Pig. 48.— BDDEECKIA califounica. (See page 300.) 
There is but little doubt that many discrepancies observed in the 
action of special manures are due to this cause. But little good, 
of course, will result from the application of special manures in 
cases where the soil already contains a sufficient quantity of the 
food constituents supplied in the manure. Great injustice has 
been done to artificial manures, and their efficacy has often been 
questioned, in consequence of their indiscriminate use on soils 
which do not actually require them. 
Excepting the facts known regarding the special requirements 
of our ordinary cultivated crops, the cultivator has but little to 
guide him in the application of special manures. It is often a 
question whether this or that manure, which perhaps he could 
obtain at a moderate cost, would have a beneficial effect upon his 
soil, and whether the result would be such as to compensate the 
expense involved. At present he knows but little of the latent 
resources of his soil beyond that he obtains from a knowledge of 
the crops which succeed best on it. This knowledge, although 
only of a comparative nature, is, however, of considerable value ; 
for instance, suppose he finds that he can grow fair crops of corn 
but cannot succeed with root crops, from inference he may con¬ 
clude that his soil was most probably deficient in phosphates. 
The actual amount of food constituents in the soil, whether in 
the latent or available conditions, can only be ascertained by 
means of an analysis, which requires to be made by persons 
having the requisite skill and chemical knowledge. By means of 
an analysis the composition of the soil can be compared with 
