THE CULTIVATOR. 
On the Practical Value of the Analyses of Plants. 
S. W. JOHNSON. 
In a former paper* I have endeavored to discuss 
impartially the value of soil-analyses. This question 
was considered in reference to the assumed principle, 
that as the qualitative (ash) analysis of a plant fur¬ 
nishes directly a correct notion of what must exist in 
the soil in order to grow the plant ,—so the quantitative 
analysis of a plant is a -guide in adding the needful 
substances in proper quantity and proportion. I now 
propose to lay before your readers certain statements 
which seem to prove that the principle in italics is it¬ 
self incorrect, and that the analyses of plants as hither¬ 
to interpreted , to American farmers, are of little practi¬ 
cal value, and indeed have been made the basis of 
false doctrine. In making and sustaining this asser¬ 
tion, nothing is said derogatory to science or to its 
genuine cultivators. What is incorrect does not belong 
to science, although that which is only partially true, 
must often be provisionally accepted by scientific men, 
until they ean discover and reject its errors. 
Nothing was more natural than to conclude from the 
analysis of the ashes of a giant, that silica, phosphoric 
aeid, and the other constantly present mineral ingredi¬ 
ents, must oecur in the soil which is destined to nourish 
that plant. This conclusion has been so fully and deci¬ 
dedly confirmed, that it must be accepted as a fixed 
fact.” A closely related deduction was drawn from 
comparing the analyses of different crops. It was 
said that the grains contain much phosphoric acid, 
root-crops much potash and soda, grasses much lime 
and silica. It was therefore inferred that these crops 
need especially, to their luxurious growth, that the 
substances respectively mentioned, be largely present 
in the soiL At first a great error was committed by 
comparing the analyses of single parts of one plant, 
with the whole of another, instead of bringing the 
complete plant into account in all instances. Thus in 
case of wheats only the ripe grain—in that of grass, 
the whole of the plant except the root,—while with 
the turnip only the root was brought into the compari¬ 
son. It is perfectly obvious that the root, stalk and 
leaves of wheat must attain a normal development be¬ 
fore the grain ean be formed, and unless the leaves of 
the turnip manifest by size and color a healthy con¬ 
dition, it eaimot be expeeted that the root will grow. 
The plant is in an agricultural sense, an individual, 
all of whose parts are necessary to each other and to 
the whole .j consequently, considerations deduced from 
a study of a part must have a doubtful value. At 
first, too, analyses were directly compared as they came 
from the chemist’s note book, expressed in per eents. 
In wheat, for example, was found 50 per cent, phos¬ 
phoric acid, and 20 potash—in turnips, 7 per cent, of 
the former, and 45 of the latter. This seemed to leave 
no doubt that phosphates were of the greatest impor¬ 
tance to the wheat crop, while potash must be an in¬ 
dispensable application to turnips. When, however, 
* See Cull, for 1854, p. 233. 
we calculate the phosphoric acid removed from an acre, 
we find that more is contained in 25 tons of turnips, 
than in 25 bushels of wheat. It then became fashiona¬ 
ble to analyze the plant more completely, and to cal¬ 
culate how much it would remove from the soil, and 
recipes were given to replace the missing quantities. 
The illustrious Liebig went so far as to cause the 
manufacture of special manures on a large scale. But 
the discordant results of analysis ought then to have 
given a new direction to study. We often find, in com¬ 
paring different analyses of the same kind of plant, 
differences of 10 and even 20 per cent, in some ingre¬ 
dients. We know in fact, that we can influence the 
composition of the ash to a considerable extent, by di¬ 
rect application to the soil. The structure of the plant 
is such as admits the moisture of the soil to pass up 
constantly through its roots and stern. Whatever is 
in the soil, soluble in water, must also take the same 
route, whether it be just what the plant needs, both in 
quality and quantity, or more. Any excess of water 
entering the plant, evaporates aga n from the leaves, 
but the salts that were dissolved in the water, remain 
in the tissues of the plant, where they may often be 
seen by aid of the microscope in beautiful crystals. 
It is impossible now to say how much of these sub¬ 
stances is just Sufficient for this plant, though we know 
that.it will fail to develop itself if there be a want of 
these, and will be injured by too great an excess. 
There is doubtless a considerable space between the 
two limits—a space within which the variations may 
be harmless. It is then plain that the composition of 
the ash of a plant is, to a certain extent, accidental. 
It is only from a great number of analyses, that we 
can derive an average that shall represent the normal 
composition of the ashes of a plant. 
It is now assumed by the best authorities, as the re¬ 
sult of the most reliable investigations, that phospho¬ 
ric aeid, silica, lime, magnesia and potash, are the 
most essential ingredients of cultivated crops. Chlo¬ 
rine, soda, sulphuric acid, iron and manganese, though 
doubtless essential at least to some parts of plants, 
nevertheless are subject to the greatest variations, and 
in most cases are needful only in very small quantity. 
I copy here a table drawn up by Wolff, from the 
most recent analyses, (the older ones were very errone¬ 
ous in some points) which gives an average, of the 
quantity of the more important bodies removed from a 
hectare of land in a good yield of the ordinary crops. 
The weights and measures of the original are retain¬ 
ed, as the value of the numbers is chiefly eompara- 
ive. 1 hectare = 2.47 acres—1 kilogramme = 22.8 
lbs. 
[For Table, see top of 1st column on next page.] 
In comparing these numbers, it is seen that the 
quantity of nitrogen is nearly alike in all the cereals, 
and in meadow hay—while the quantity contained in 
the produce of a hectare of beans, peas, beats, potatoes 
and clover, is double so much. The amount of phos¬ 
phoric aeid does not vary very greatly throughout, if 
we except beans and beets, in which it is above, and 
meadow hay in whieh it falls below the average 
