are essentially of a mineral nature. The quantity of organic matter in
such soils may vary from a mere trace to a few per cent, but they never
lose their mineral predominance. When a soil on the other hand is
composed almost exclusively of vegetable mold it belongs to quite
another type. Such soils are called tule, peat or muck. In this country
there are thousands of acres of peat or muck soils; the largest
contiguous deposits being found in Southern Florida. The origin of these
soils is easily understood. Whenever rank vegetation grows in such a
location as to secure for the organic matter formed a slow decay there
is a tendency to the accumulation of vegetable mold in shallow water or
on marshy ground and where conditions are favorable to such
accumulations. In Florida the muck soils have been accumulated about the
margins of lakes. During the rainy season the marshes bordering these
are partly covered with water, but the vegetation is very luxuriant. The
water protects the vegetable matter from being destroyed by fire. It
therefore accumulates from year to year and is gradually compacted into
quite a uniform mass of vegetable mold.
The composition of the muck is illustrated in the following table which
shows the character of the layers at one, two and three feet in
depth:[35]
Carbon. Hydrogen. Nitrogen. Volatile
matter.
1 foot 57.67 per cent 4.48 per cent 2.24 per cent 90.60 per cent
2 feet 47.07 „ 5.15 „ 1.40 „ 72.00 „
3 feet 8.52 „ 0.53 „ 0.31 „ 15.00 „
In this sample, No. 3, the muck was only three feet deep, resting on
pure sand. As the bottom of the deposit is approached the admixture of
sand becomes greater and the percentage of organic matter less.
No reliable estimate of the time which has been required to form these
deposits can be given, but in the Okeechobee region in Florida the
deposit of vegetable mold in some places exceeds ten feet in depth.
The purest muck or peat soils contain only small quantities of potash
and phosphoric acid, and especially is this true of the Florida mucks
which have been formed of vegetable growth containing very little
mineral matter.
It is not at all probable that the flora now growing on any particular
area of virgin peat contains all the plants that have contributed to its
formation. The principal vegetable growths now going to make up the muck
soils of Florida are the following:
Common names. Botanical names.
Saw grass Cladium effusum
Yellow pond lily Nymphea flava
Maiden cane grass Panicum Curtisii
Alligator Wampee Pontederia cordata
Sedge Cyperus species
Fern brake Osmunda „
Mallow Malva „
Broom sedge Andropogon „
Arrow weed Sagittaria „
The above are only the plants growing in the greatest profusion and do
not include all which are now contributing to increase the store of
vegetable débris.
=52. Humus.=—The active principle of vegetable mold is called humus, a
term used to designate in general the products of the decomposition of
vegetable matter as they are found in soils. In peat and muck are found
a mixture of humus with undecomposed or partially decomposed vegetation.
According to Kostytchoff[36] vegetable matter decays under the influence
of molds and bacteria. Molds alone produce the dark colored matters
which give soils rich in vegetable matter, their color. One chief
characteristic of humus is its richness in nitrogen. Black Russian soil
contains from 4 to 6.65 per cent of nitrogen. This soil is estimated to
contain sixty million organisms per gram and much of the nitrogen which
it holds must be in the form of proteids. The first development in
decaying vegetable matter is of bacteria and there is a tendency of the
decaying matter to become acid. This causes a decay of the bacteria and
the ammonia produced by this neutralizes the acid. The various kinds of
mold grow when the reaction becomes neutral. Afterwards the bacteria and
the molds develop together. This statement of Kostytchoff is not a very
satisfactory explanation of even our limited knowledge of the
decomposition of organic matters in the soil. Ammonia and ammonia salts
are formed not by the decay of some forms of bacteria but by the
activities of other forms. Warington found that in nitrification there
were three distinct forms of bacteria concerned in the final products of
ammonia, nitrites, and nitrates. Humus always contains easily
decomposable matter and consequently the rate of decay at any observed
periods is nearly the same. In humus which is produced above the
water-level Kostytchoff states that all trace of the vegetable structure
is destroyed by the leaves being gnawed and passed through the bodies of
caterpillars and wire-worms. Under the water-level the vegetable
structure is preserved and peat results. The decay of humus is most
rapid in drained and open soils. For this reason the presence of clay in
a soil promotes the accumulation of humus. Inferior organisms are the
means of diffusing organic matter through the soil. The mycelia of fungi
grow on a dead root for instance, ramify laterally and thus carry
organic matter outward and succeeding organisms extend this action and
the soil becomes darkened in proportion. Humic acid in black soil is
almost exclusively in combination with lime.
A more common view of the difference between the formation of humus
above and below the water-level is that above the water-level there is a
very free access of air and even the harder parts of the leaf skeleton
can be oxidized through the agency of bacteria, while under the
water-level there is a very limited supply of air and this oxidation
cannot proceed as rapidly. The harder parts of the leaf skeleton are
preserved, and from the freer access of air humus is oxidized more
readily in drained and open soils, and accumulates in clay soils where
there is less circulation of air.
The real composition of humus is a matter which has never been
definitely determined. Composed of many different but closely related
substances it has been difficult to isolate and determine them.
Stockbridge[37] gives the following composition of the bodies which form
the larger part of humus:
Ulmin and Ulmic Acid.
Carbon 67.1 per cent Corresponding to C₄₀H₂₈O₁₂ + H₂O.
Hydrogen 4.2 „ „
Oxygen 8.7 „ „
Humin and Humic Acid.
Carbon 64.4 per cent Corresponding to C₂₁H₂₄_O₁₂ + 3H₂O
Hydrogen 4.3 „ „
Oxygen 31.3 „ „
Crenic Acid.
Carbon 44.0 per cent Corresponding to C₁₂H₁₂O₈?
Hydrogen 5.5 „ „
Nitrogen 3.9 „ „
Oxygen 46.6 „ „
Apocrenic Acid.
Carbon 34.4 per cent Corresponding to C₂₄H₂₄O₁₂?
Hydrogen 3.5 „ „
Nitrogen 3.0 „ „
Oxygen 39.1 „ „
He further states that there are, aside from these humus compounds,
others still less known and the action of which is not yet understood;
among them xylic acid, C₂₄H₃₀O₁₇, saccharic acid, C₁₄H₁₈O₁₁, glucinic
acid, C₁₂H₂₂O₁₂, besides a brown humus acid containing carbon, 65.8 per
cent, and hydrogen, 6.25 per cent, and a black humus acid yielding
carbon, 71.5 per cent, and hydrogen, 5.8 per cent.
According to Mulder humic acid has the following composition, C₆₀H₅₄O₂₇,
while Thenard[38] ascribes to it the formula, C₂₄H₁₀O₁₀.
At the present time we can only regard the various forms of humus bodies
as mixtures of many substances mostly of an acid nature and resulting
from a gradual decomposition of organic matter under conditions which
partially exclude free access of oxygen.
For analytical purposes it is only necessary to separate these bodies by
the best approved processes. A further knowledge of their composition
can then be derived by determining the percentages of carbon dioxid and
water which they yield on combustion.
=53. Soil and Subsoil.=—Many subdivisions have been made of the above
varieties of soil, but they have little value for analytical purposes.
For convenience in description for agricultural purposes, the soil,
however, is further divided into soil and subsoil. In this sense the
soil comprises that portion of the surface of the ground, usually from
four to nine inches deep, containing most of the organic remains of
plants and animals and in which air circulates more or less freely for
the proper humification of the organic matter, which usually gives a
darker color to the soil than to the subsoil. The subsoil proper lies
below this, and has usually more characteristic properties, especially
in respect of color and texture, as it has been less influenced by
artificial conditions of cultivation and the remains of vegetation.
The subsoil extends to an indefinite depth and is limited usually by
deposits of undecomposed or partly decomposed rock matter, or by layers
of clay, sand or gravel.
Inasmuch, however, as the influence of the subsoil on growing crops is
of little importance below the depth of eighteen inches the analysis of
samples from a greater depth has more of a geologic than agricultural
value.
Hilgard regards as subsoil whatever lies beneath the line of change, or
below the minimum depth of six inches. But should the change of color
occur at a greater depth than twelve inches, the soil specimen should
nevertheless be taken to the depth of twelve inches only, which is the
limit of ordinary tillage; then another specimen from that depth down to
the line of change, and then the subsoil specimens beneath that line.
The depth to which the last should be taken will depend upon
circumstances. It is always desirable to know what constitutes the
foundation of a soil to the depth of three feet at least, since the
question of drainage, resistance to drought, etc., will depend
essentially upon the nature of the substratum. But in ordinary cases ten
or twelve inches of subsoil will be sufficient. The sample should be
taken in other respects precisely like that of the surface soil, while
that of the material underlying this subsoil may be taken with less
exactness, perhaps at some ditch or other easily accessible point, and
should not be broken up like the other specimens.
In the method of soil sampling adopted by the Royal Agricultural College
of England, the soil is regarded as that portion of the surface of the
ground which is reached by ordinary tillage operations, generally being
from six to nine inches deep; the subsoil is that portion which is
ordinarily not touched in plowing.
AUTHORITIES CITED IN PART FIRST.
Footnote 1:
Comptes rendus, Tome 110, p. 1271.
Footnote 2:
Wyatt, Phosphates of America, p. 66.
Footnote 3:
Engineering and Mining Journal, August 23, 1890.
Footnote 4:
American Journal of Science, Vol. 41, February, 1891.
Footnote 5:
Preliminary Sketch of Florida Phosphates, Author’s edition, pp. 18, et
seq.
Footnote 6:
Journal für praktische Chemie, 1st series, Band 38, S. 388.
Footnote 7:
Annual Report Connecticut Experiment Station, 1890, p. 72.
Footnote 8:
Annual Report Massachusetts Experiment Station, 1887, p. 233.
Footnote 9:
Bulletin 21, Rhode Island Experiment Station, 1893.
Footnote 10:
Chemical Composition of Food-Fishes. Report of U. S. Commissioner of
Fish and Fisheries, 1888, pp. 679 et seq.
Footnote 11:
G. Brown Goode, American Naturalist, Vol. 14, July, 1890.
Footnote 12:
Comptes rendus, Tome 101, 1885, pp. 65, et seq.
Footnote 13:
Royal Agricultural Society Journal, Vol. 13, 1852, pp. 349 et seq.
Footnote 14:
Gîtes Mineraux, par Fuchs et DeLauny, Tome 1, p. 425.
Footnote 15:
El Salitre de Chile; René F. LeFeuvre y Artūro Dagnino, 1893, p. 12.
Footnote 16:
Crampton, American Chemical Journal, Vol. II, 1890, p. 227.
Footnote 17:
Potash, pamphlet of German Kali Works, pp. 3, 4.
Footnote 18:
Gîtes Mineraux, p. 429.
Footnote 19:
Bulletin of the Philosophical Society of Washington, Vol. II, p. 142.
Footnote 20:
Handbook for the Department of Geology of the U. S. National Museum,
by Geo. P. Merrill.
Footnote 21:
Vid. supra, p. 506.
Footnote 22:
Vid. supra, Plate 120.
Footnote 23:
Merrill, op. cit. p. 521.
Footnote 24:
Merrill, op. cit. p. 536.
Footnote 25:
Merrill, op. cit. p. 545.
Footnote 26:
Merrill, op. cit. p. 547.
Footnote 27:
Mineral Physiology and Physiography, p. 251.
Footnote 28:
Bulletin No. 52, United States Geological Survey, p. 16.
Footnote 29:
bis (p. 48), Vid. supra, p. 38.
Footnote 30:
The Formation of Vegetable Mold through the Action of Worms.
Footnote 31:
Rocks and Soils, pp. 131–2.
Footnote 32:
Comptes rendus, Tome 110, p. 1370.
Footnote 33:
Bulletin No. 83, California Experiment Station.
Footnote 34:
Geological Magazine, Vol. 7, No. 6, pp. 291–92.
Footnote 35:
Wiley, Agricultural Science, 1893, pp. 106 et seq.
Footnote 36:
Travaux de la Société des Naturalistes St. Petersburg, Tome 20, 1889.
Footnote 37:
Rocks and Soils, p. 134.
Footnote 38:
Beilstein’s Handbuch der Organischen Chemie, Band I, Ss. 891–2.
PART SECOND.
TAKING SAMPLES OF SOIL FOR ANALYSIS.
=54. General Principles.=—It would be unwise to attempt to give any
single method of taking soil samples as the only one to be practiced in
all circumstances. In the methods which follow it is believed will be
found directions for every probable case. The particular method to be
followed will in each case have to be determined by circumstances.
The sole object in taking a sample of soil should be to have it
representative of the type of soils to which it belongs. Every
precaution should be observed to have each sample measure up to that
standard.
The physical and chemical analyses of soils are long and tedious
processes and are entirely too costly to be applied to samples which
represent nothing but themselves.
The particular place selected for taking the samples as well as the
method employed are also largely determined by the point of view of the
investigations. The collection of samples to illustrate the geologic or
mineralogical relations of soils is quite a different matter from
gathering portions to represent their agricultural possibilities. In a
given area the sum of plant food in the soil would only be determined by
the analyses of samples from that particular field, while samples
illustrating geologic relations could or should be taken at widely
distant points. Again the chemist is content with a sample of a few
grams in weight while the physicist would require a much larger
quantity. Much popular ignorance exists respecting the importance of the
collection of soil samples. As an illustration of this may be cited a
recent instance in which a sample of soil was received by the author
with a request for a complete analysis and a statement of the kinds of
crops it was suited to grow. No data relating to the locality in which
the sample was taken accompanied this request. The sample itself, which
weighed a little less than 3.6 grams, was not a soil at all in an
agricultural sense but a highly ferruginous sand.
The collector of samples who understands the purpose for which he is
working will find among the approved methods which follow some one or
some combination of methods, by means of which his work can be made
successful. In these cases it is the collector rather than the method on
which reliance must be placed to secure properly representative samples.
=55. General Directions for Sampling.=—The locality having been selected
which presents as nearly as possible the mean composition of the field a
square hole is dug with a sharp spade to the depth of eighteen inches.
The walls of this hole should be smooth and perpendicular. The soil to
the depth of six to nine inches is then removed from the sides of the
hole in a slice about four inches thick; or the sample of soil may be
taken to the depth indicated by a change of color. Any particles which
fall into the bottom of the hole are carefully collected and added to
the parts adhering to the spade. The whole is thrown into a suitable
vessel for removal to the laboratory. The sample of soil having been
thus secured, the subsoil is taken in the same way. To insure uniformity
in the samples, it is well to take several of them from the same field.
Where more than one sample is taken it is advisable to mix all the
sub-samples in the field, remove large sticks, stones, roots, etc., and
take a general sample of from three to five kilograms. The character of
the débris, etc., removed should be carefully noted.
It is sometimes desirable to take samples of the subsoil to a greater
depth than eighteen inches. A post-hole auger or large wood auger will
be found very useful for this purpose. It is rarely necessary to take
samples of subsoil to a greater depth than six feet. In taking samples
the geologic formation and the general topography of the field should be
noted, also the character of the previous crops, kind and amount of
fertilizers employed, character of drainage and any other data of a
nature to give a more accurate idea of the forces which have determined
the physical and chemical properties of the sample.
=56. Method Of Hilgard.=—Hilgard[39] recommends that samples should not
be taken indiscriminately from any locality you may chance to be
interested in, but that you should consider what are the two or three
chief varieties of soil which, with their intermixtures, make up the
cultivable area of your region, and carefully sample these first of all.
As a rule, and whenever possible, samples should be taken only from
spots that have not been cultivated, or are otherwise likely to have
been changed from their original condition of virgin soils and not from
ground frequently trodden over such as roadsides, cattle paths, or small
pastures, squirrel holes, stumps, or even the foot of trees, or spots
that have been washed by rains or streams, so as to have experienced a
noticeable change, and not be a fair representative of their kind. He
further suggests that the normal vegetation, trees, herbs, grass, etc.,
should be carefully observed and recorded, and spots showing unusual
growth be avoided whether in kind or quality, as such are likely to have
received some animal manure or other outside addition.
Specimens should be taken from more than one spot judged to be a fair
representative of the soil intended to be examined as an additional
guarantee of a fair average.
After selecting a proper spot pull up the plants growing on it, and
scrape off the surface lightly with a sharp tool to remove half-decayed
vegetable matter not forming part of the soil. Dig a vertical hole, like
a post-hole, at least 20 inches deep. Scrape the sides clean so as to
see at what depth the change of tint occurs which marks the downward
limit of the surface soil, and record it. Take at least half a bushel of
the earth above this limit, and on a cloth (jute bagging should not be
used for this purpose, as its fibers, etc., become intermixed with the
soil) or paper break it up and mix thoroughly, and put up at least a
pint of it in a sack or package for examination. This specimen will,
ordinarily, constitute the soil. Should the change of color occur at a
less depth than six inches the fact should be noted, but the specimen
taken to that depth nevertheless, since it is the least to which
rational cultures can be supposed to reach.
In case the difference in the character of a shallow surface soil and
its subsoil should be unusually great, as may be the case in tule or
other alluvial lands or in rocky districts, a separate example of that
surface soil should be taken, besides the one to the depth of six
inches.
Specimens of salty or alkali soils should, as a rule, be taken only
toward the end of the dry season, when they will contain the maximum
amount of the injurious ingredients which it may be necessary to
neutralize.
Whatever lies beneath the line of change, or below the minimum depth of
six inches, will constitute the subsoil. Should the change of color
occur at a greater depth than twelve inches the soil specimen should
nevertheless be taken to the depth of twelve inches only, which is the
limit of ordinary tillage; then another specimen from that depth down to
the line of change, and then the subsoil specimen beneath that line.
Hilgard justly calls attention to the fact that all peculiarities of the
soil and subsoil, their behavior in wet and dry seasons, their location,
position and every circumstance in fact, which can throw any light on
their agricultural qualities or peculiarities should be carefully noted
and the notes sent with the samples. Unless accompanied by such
information, samples can not ordinarily be considered as justifying the
amount of labor involved in their examination.
=57. Whitney=[40] suggests that a geologic map of the region to be
sampled should always be at hand and that all samples should be rejected
from spots showing local discrepancies, washings or other disturbances.
The kind of analyses to which a sample is to be subjected also largely
determines the method to be pursued in selecting it: For instance, a
sample to be used for determining the size of the particles therein, may
be taken in quite a different manner from that designed only for the
determination of moisture.
=58. In= the directions collated by Richards[41] and which have been
largely followed by the correspondents of the Department of Agriculture,
it is recommended to select in a field, four or five places, at least,
per acre, taking care that these places have an homogeneous aspect, and
represent as far as possible the general character of the whole ground.
If the field, however, present notable differences, either in regard to
its aspect or its fertility, the samples gathered from the different
parts must be kept separate.
The sampling of arable soil should be made only after the raising of the
crop and before it has received any new manure. In other soils the
sample should be taken only from spots that have not been cultivated.
=59. In= the method of soil sampling adopted by the German Experiment
Stations[42] it is directed that the samples of soil should be taken
according to the extent of the surface to be sampled, in three, five,
nine, twelve or more places at equal distances from each other. They
should be taken in perpendicular sections to the depth turned by the
plow; and for some studies of the subsoil to a depth of sixty to ninety
centimeters. The single samples can be either examined separately or
carefully mixed and an average portion of the mixture taken.
=60. Method of the Official French Commission.=—The official French
commission[43] emphasizes the fact that the sample of soil taken for
analysis, should represent a layer of equal thickness through the total
depth of its arable part. An analysis of the subsoil taken in the same
way, will often be useful to complete the data of the soil study.