Chapter IV: Introduction (3)

The nitrifying ferment is exercised on a much larger scale in the normal conditions of the lower levels where the rock is covered with earth. This activity is not limited to the mass of rock but is continued upon the fragments of the most diverse size scattered through the soil and it gradually reduces them to a state of fine particles. It is therefore a phenomenon of the widest extension.

The action of these micro-organisms according to Müntz is not confined to the surface but extends to the most interior particles of the rocky mass. Where, however, there is nothing of a nitrogenous nature, to nitrify such an organism must live in a state of suspended animation.

When the extreme minuteness of these phenomena is considered there may be a tendency to despise their importance, but their continuity and their generality in the opinion of Müntz place them among the geologic causes to which the crust of the earth owes a part of its actual physiognomy and which particularly have contributed to the formation of the deposits of the comminuted elements constituting arable soil.

The general action of nitrifying organisms in the soil, the nature of these bodies, and the method of isolating and identifying them will be fully discussed in another part of this work.

=46. Action of the Air.=—The air itself takes an active part in rock decay. Wherever rocks are exposed to decay, there air is found or, at least, the active principle of air, _viz._, oxygen. The air not only penetrates to a great depth in the earth, but is also carried to much greater depths by water which always holds a greater or less quantity of air in solution. The oxygen of the air is thus brought into intimate contact with the disintegrating materials and in a condition to assist wherever possible in the decomposing processes.

The oxygen acts vigorously on the lower oxids of iron, converting them into peroxids, and thus tends to produce decay.

There are other constituents of rocks which oxygen affects injuriously and thus helps to their final breaking up. It is true that, as a rule, the constituents of rocks are already oxidized to nearly as high a degree as possible, and on these constituents of course the air would have no effect. But on others, especially when helped by water with the other substances it carries in solution, the air may greatly help in the work of destruction.

In a general view, the action of the air in soil formation may be regarded as of secondary importance, and to depend chiefly on the oxidation of the lower to the higher basic forms. These processes, while they seem of little value, have, nevertheless, been of considerable importance in the production of that residue of rock disintegration which constitutes the soil.

=47. Classification of Soils According to Deposition.=—In regard to their deposition soils are divided into five classes:

1. Those which are formed from the decomposition of crystalline or sedimentary rocks or of unconsolidated sedimentary material _in situ_.

2. Those which have been moved by water from the place of their original formation and deposited by subsidence (bottom lands, alluvial soils, lacustrine deposits, etc.).

3. Those which have been deposited as débris from moving masses of ice (glacial drift).

4. Soils formed from volcanic ashes or from materials moved by the wind and deposited in low places or in hills or ridges.

5. Those formed chiefly from the decay of vegetable matter, (tule, peat, muck).

=48. Qualities of Soils.=—In respect of quality, soils have been arbitrarily divided into many kinds. Some of the more important of these divisions are as follows:

1. _Sand._ Soils consisting almost exclusively of sand.

2. _Sandy Loams._ Soils containing some humus and clay but an excess of sand.

3. _Loams._ Soils inclining neither to sand nor clay and containing some considerable portions of vegetable mold, being very pulverulent and easily broken up into loose and porous masses.

4. _Clays._ Stiff soils in which the silicate of alumina and other fine mineral particles are present in large quantity.

5. _Marls._ Deposits containing an unusual proportion of carbonate of lime, with often some potash or phosphoric acid resulting from the remains of sea-animals and plants.

6. _Alkaline._ Soils containing carbonate and sulfate of soda, or an excess of these alkaline and other soluble mineral substances.

7. _Adobe._ A fine grained porous earth of peculiar properties hereinafter described.

8. _Vegetable._ Soils containing much vegetable débris in an advanced state of decomposition. When such matter predominates or exists in large proportion in a soil the term tule, peat or muck is applied to it.

With the exception of numbers six, seven and eight these types of soil are so well-known as to require no further description for analytical purposes. The alkaline, adobe and vegetable soils on the contrary demand further study.

=49. Alkaline Soils.=—The importance of a more extended notice of this class of soils for analytical purposes is emphasized by their large extent in the United States.

Chiefly through the researches of Hilgard attention has been called to the true character of these soils which are found throughout a large part of the Western United States and which are known by the common name of alkali. The following description of the origin of these soils is compiled chiefly from Hilgard’s papers on this subject. Wherever the rain-fall is scanty, and especially where the rains do not come at any one time with sufficient force to thoroughly saturate the soil and carry down through the subsoil and off through the drainage waters the alkali contained therein, favorable conditions exist for the production of the alkaline soil mentioned above. The peculiar characteristic of this soil is the efflorescence which occurs upon its surface and which is due to the raising of soluble salts in the soil by the water rising through capillary attraction and evaporating from the surface, leaving the salts as an efflorescence.

Soils which contain a large amount of alkali are usually very rich in mineral plant food, and if the excess of soluble salt could be removed, these lands under favorable conditions of moisture would produce large crops.

The formation of the alkali may be briefly described as follows: By the decomposition of the native rocks, certain salts soluble in water are formed. These salts in the present matter are chiefly sodium and potassium sulfates, chlorids and carbonates. The salts of potash together with those of lime are more tenaciously held by the soil than the soluble salts of soda, and the result of this natural affinity of the soil for soluble potash, lime and magnesian salts is seen in the formation at the surface of the earth, by the process of evaporation above described, of a crust of alkaline material which is chiefly composed of the soluble salts of soda. In countries which have a sufficient amount of rain-fall, these soluble salts are carried away either by the surface drainage or by the percolation of water through the soil, and the sodium chlorid is accumulated in this way in the waters of the ocean. But where a sufficient amount of rain-fall does not occur, these soluble salts carried down by each shower only to a certain depth rise again on the evaporation of the water, reinforced by any additional soluble material which may be found in the soil itself. The three most important ingredients of the alkali of the lands referred to are sodium chlorid, sulfate, and carbonate. When the latter salt, namely, sodium carbonate, is present in predominant quantity, it gives rise to what is popularly known as black alkali. This black color is due to the dark colored solution which sodium carbonate makes with the organic matters or humus of the soil. The black alkali is far more injurious to growing vegetation than the white alkali composed chiefly of sodium sulfate and chlorid.

This black alkali has been very successfully treated by Hilgard[33] by the application of gypsum which reacting with the sodium carbonate produces calcium carbonate and sodium sulfate, thus converting the black into the white alkali and adding an ingredient in the shape of lime carbonate to stiff soils which tends to make them more pulverulent and easy of tillage.

This method of treatment, however, as can be easily seen, is only palliative, the whole amount of the alkaline substances being still left in the soil, only in a less injurious form.

The only perfect remedy for alkaline soils, as has been pointed out by Hilgard, is in the introduction of underdrainage in connection with irrigation. The partial irrigation of alkaline soils, affording enough moisture to carry the alkali down to and perhaps partially through the subsoil, can produce only a temporary alleviation of the difficulties produced by the alkali. Subsequent evaporation may thus increase the amount of surface incrustation. For this reason in many cases the practice of irrigation without underdrainage may completely ruin an otherwise fertile soil by slowly increasing the amount of alkali in the soil by the total amount of the alkaline material added in the waters of irrigation.

As Hilgard has pointed out, if a soil can be practically freed from alkali by underdrainage connected with a thorough saturation by irrigation, it may be centuries before the alkali will accumulate in that soil again when ordinary irrigation only is practiced. It may thus become possible to reclaim large extents of alkaline soil little by little by treating them with an excess of irrigation water in connection with thorough underdrainage. The composition of the alkali on the surface of the soil due to the causes above set forth is thoroughly illustrated by the analyses of Hilgard and Weber, which follow:

TABLE SHOWING COMPOSITION OF ALKALI SALTS IN SAN JOAQUIN VALLEY.

═════════════╤════════════════════════════════════════════
│ FRESNO COUNTY.
─────────────┼────────────────────────────────────────────
│ Sections 13 and 24 T. 14 S. R. 19 E., 4
│ miles S. W. from Fresno.
│
─────────────┼────────┬───────────────────────────────────
│ Alkali │ Alkali Spot, 1889.
│ soil, │
│ 1888. │
─────────────┼────────┼────────┬────────┬────────┬────────
│ „ │ 1 inch │ 18 │ 26 │ 42
│ │surface.│ inches │ inches │ inches
│ │ │ bel. │ bel. │hardpan.
│ │ │surface.│surface.│
─────────────┼────────┼────────┼────────┼────────┼────────
Soluble salts│ │ 0.76 │ 0.20 │ 0.18 │ 0.16
in 100 │ │ │ │ │
parts soil │ │ │ │ │
Potassium │ │ │ │ │
sulfate │ │ │ │ │
[D]Potassium │ │ │ │ │
nitrate │ │ │ │ │
Potassium │ │ │ │ │
carbonate │ │ │ │ │
(Saleratus)│ │ │ │ │
Sodium │ large │ small │ small │ very │ very
sulfate │ │ │ │ slight │ slight
(Glauber’s │ │ │ │ │
salt) │ │ │ │ │
Sodium │ very │ large │ small │ large │ large
carbonate │ slight │ │ │ │
(Sal-soda) │ │ │ │ │
Sodium │chiefly │moderate│chiefly │moderate│moderate
chlorid │ │ │ │ │
(Common │ │ │ │ │
salt) │ │ │ │ │
[D]Sodium │ │ │ │ │
phosphate │ │ │ │ │
Calcium │moderate│ small │ very │ very │ very
sulfate │ │ │ slight │ slight │ slight
(Gypsum) │ │ │ │ │
Magnesium │ │ │ │ │
sulfate │ │ │ │ │
(Epsom │ │ │ │ │
salt) │ │ │ │ │
Organic │ │ │ │ │
matter │ │ │ │ │
─────────────┴────────┴────────┴────────┴────────┴────────

═════════════╤══════════════════════════════════════════════════
│ FRESNO COUNTY.
─────────────┼────────────────┬────────────────┬───────┬────────
│ Miss Austin’s │ N.W. Cor. N ½ │Easton.│Emigr’nt
│ Ranch, Central │Sec. 20 T. 14 S.│ │ Ditch.
│ Colony. │ R. 21 E. │ │
─────────────┼───────┬────────┼───────┬────────┼───────┼────────
│Surface│Surface │Surface│Surface │ „ │ „
│ soil, │ soil, │ soil. │ soil. │ │
│No. 1. │ No. 2. │ │ │ │
─────────────┼───────┼────────┼───────┼────────┼───────┼────────
│ „ │ „ │ „ │ „ │ „ │ „
│ │ │ │ │ │
│ │ │ │ │ │
│ │ │ │ │ │
─────────────┼───────┼────────┼───────┼────────┼───────┼────────
Soluble salts│ 3.54 │ 1.90 │ 1.20 │ 2.69 │ │
in 100 │ │ │ │ │ │
parts soil │ │ │ │ │ │
Potassium │ small │moderate│ │ │ │
sulfate │ │ │ │ │ │
[D]Potassium │ │ small │ │ │ │
nitrate │ │ │ │ │ │
Potassium │ │ │ │ │ │
carbonate │ │ │ │ │ │
(Saleratus)│ │ │ │ │ │
Sodium │ large │ large │ much │moderate│ large │
sulfate │ │ │ │ │ │
(Glauber’s │ │ │ │ │ │
salt) │ │ │ │ │ │
Sodium │ small │chiefly │ small │ small │ │chiefly
carbonate │ │ │ │ │ │
(Sal-soda) │ │ │ │ │ │
Sodium │chiefly│ large │chiefly│chiefly │ large │ little
chlorid │ │ │ │ │ │
(Common │ │ │ │ │ │
salt) │ │ │ │ │ │
[D]Sodium │ │ │ │ │ │
phosphate │ │ │ │ │ │
Calcium │ small │moderate│ small │ small │ much │
sulfate │ │ │ │ │ │
(Gypsum) │ │ │ │ │ │
Magnesium │ │ small │ │ │ much │
sulfate │ │ │ │ │ │
(Epsom │ │ │ │ │ │
salt) │ │ │ │ │ │
Organic │ │ │ │ │ │
matter │ │ │ │ │ │
─────────────┴───────┴────────┴───────┴────────┴───────┴────────
Footnote D:

Very generally present, but not always in quantities sufficient for
determination.

═════════════════════╤═════════════════════════════════════════════════ │ TULARE COUNTY. ─────────────────────┼───────┬───────┬────────┬───────┬────────┬─────── │Goshen │Peopl’s│ Near │Visalia│Lemoore │Tulare │ │ Ditch │ Lake │ │ │ Exp’t │ │ │ Tulare │ │ │Station ─────────────────────┼───────┼───────┼────────┼───────┼────────┼─────── │Surf’ce│Alkali │Surf’ce │Surf’ce│ Alkali │Alkali │ soil │ crust │ soil │ soil │ crust │ crust ─────────────────────┼───────┼───────┼────────┼───────┼────────┼─────── Soluble salts in 100 │ 1.40│ │ 0.83│ 1.26│ │ parts soil │ │ │ │ │ │ Potassium sulfate │ │ │ │ │ │ small [E]Potassium nitrate │ │ │ │ │ │ small Potassium carbonate │ │ │ │ 18.80│ │ (Saleratus) │ │ │ │ │ │ Sodium sulfate │ 44.24│ 1.22│31.30[F]│ 13.4│chiefly │ 32.8 (Glauber’s salt) │ │ │ │ │ │ Sodium carbonate │ 32.98│ 88.09│ 18.2│ 45.3│ │ 36.16 (Sal-soda) │ │ │ │ │ │ Sodium chlorid │ 16.74│ 1.00│ │ 4.4│ little │ 31.16 (Common salt) │ │ │ │ │ │ [E]Sodium phosphate │ 1.97│ │ 0.22│ 10.4│ │ Calcium sulfate │ │ │ │ │ little │ (Gypsum) │ │ │ │ │ │ Magnesium sulfate │ │ │ │ 8.1│moderate│ (Epsom salt) │ │ │ │ │ │ Organic matter │ 1.59│ 9.21│ 7.5│ │ │ 5.37 ─────────────────────┴───────┴───────┴────────┴───────┴────────┴───────

═════════════╤════════════════════════════════════════════════════════
│ KERN COUNTY.
─────────────┼────────────────────────────────────────────────────────
│ Alkali crusts from the Smyrna artesian belt. Townships
│ 25 and 26 R. 23 E. W. S. W. from Delano, S. P. R. R.
─────────────┼─────┬────────┬────────┬────────┬─────┬─────┬─────┬─────
│No. 1│ No. 2 │ No. 3 │ No. 4 │No. 5│No. 6│No. 7│No. 8
│ │ │ │ │ │ │ │
─────────────┼─────┼────────┼────────┼────────┼─────┼─────┼─────┼─────
Soluble salts│ │ │ │ │ │ │ │
in 100 │ │ │ │ │ │ │ │
parts soil │ │ │ │ │ │ │ │
Potassium │ │ │ │ │ │ │ │
sulfate │ │ │ │ │ │ │ │
[E]Potassium │ │ │ │ │ │ │ │
nitrate │ │ │ │ │ │ │ │
Potassium │ │ │ │ │ │ │ │
carbonate │ │ │ │ │ │ │ │
(Saleratus)│ │ │ │ │ │ │ │
Sodium │small│moderate│moderate│moderate│large│small│small│small
sulfate │ │ │ │ │ │ │ │
(Glauber’s │ │ │ │ │ │ │ │
salt) │ │ │ │ │ │ │ │
Sodium │ │ │ │ │ │ │ │
carbonate │ │ │ │ │ │ │ │
(Sal-soda) │ │ │ │ │ │ │ │
Sodium │large│moderate│ large │ large │small│large│small│large
chlorid │ │ │ │ │ │ │ │
(Common │ │ │ │ │ │ │ │
salt) │ │ │ │ │ │ │ │
[E]Sodium │ │ │ │ │ │ │ │
phosphate │ │ │ │ │ │ │ │
Calcium │small│ small │ small │ small │small│small│small│small
sulfate │ │ │ │ │ │ │ │
(Gypsum) │ │ │ │ │ │ │ │
Magnesium │small│ small │ small │ small │small│small│small│small
sulfate │ │ │ │ │ │ │ │
(Epsom │ │ │ │ │ │ │ │
salt) │ │ │ │ │ │ │ │
Organic │ │ │ │ │ │ │ │
matter │ │ │ │ │ │ │ │
─────────────┴─────┴────────┴────────┴────────┴─────┴─────┴─────┴─────

═════════════╤══════════════
│ KERN COUNTY.
─────────────┼───────┬──────
│Summer.│ Kern
│ │Island
─────────────┼───────┼──────
│Alkali │Alkali
│ crust │crust
─────────────┼───────┼──────
Soluble salts│ │
in 100 │ │
parts soil │ │
Potassium │ │ 4.72
sulfate │ │
[E]Potassium │ │
nitrate │ │
Potassium │ │
carbonate │ │
(Saleratus)│ │
Sodium │ 19.20│ 70.61
sulfate │ │
(Glauber’s │ │
salt) │ │
Sodium │ │ 14.82
carbonate │ │
(Sal-soda) │ │
Sodium │ 37.14│ 4.13
chlorid │ │
(Common │ │
salt) │ │
[E]Sodium │ │
phosphate │ │
Calcium │ 0.96│ 0.08
sulfate │ │
(Gypsum) │ │
Magnesium │ 18.31│
sulfate │ │
(Epsom │ │
salt) │ │
Organic │ 20.87│
matter │ │
─────────────┴───────┴──────
Footnote F:

Common and Glauber’s salts.

=50. Adobe Soils.=—In many parts of the arid regions of this country which can be recovered for agricultural purposes by irrigation the soil has peculiar characteristics.

The name adobe as commonly used applies to both the sundried bricks of the arid regions of the West and Southwest, and to the materials of which they are composed. The material is described by Russell[34] as a fine grained porous earth, varying in color through many shades of gray and yellow, which crumbles between the fingers, but separates most readily in a vertical direction. The coherency of the material is so great that vertical scarps will stand for many years without forming a noticeable talus slope.

_Distribution._—The area over which adobe forms a large part of the surface has not been accurately mapped, but enough is known to indicate that it is essentially co-extensive with the more arid portions of this country. In a very general way it may be considered as being limited to the region in which the mean annual rain-fall is less than twenty inches. It forms the surface over large portions of Colorado, New Mexico, Western Texas, Arizona, Southern California, Nevada, Utah, Southern Oregon, Southern Idaho, and Wyoming. Adobe occurs also in Mexico and may there reach a greater development than in the United States, but observations concerning it south of the Rio Grande are wanting.

In the United States it occurs from near the sea-level in Arizona, and even below the sea-level in Southern California, up to an elevation of at least six or eight thousand feet, along the eastern border of the Rocky Mountains, and in the elevated valleys of New Mexico, Colorado, and Wyoming. It occupies depressions of all sizes up to valleys having an area of hundreds of square miles. Although occurring throughout the arid region, it can be studied to best advantage in the drainless and lakeless basins in Nevada, Utah, and Arizona.

_Composition._—When examined under the microscope, the adobe is seen to be composed of irregular, unassorted flakes and grains, principally quartz, but fragments of other minerals are also present. An exhaustive microscopic study has not been made, but the samples examined from widely-separated localities were very similar. The principal characteristics observed were the extreme angularity of the particles composing the deposit and the undecomposed condition of the various minerals entering into its composition. It is to be inferred from this that the material was not exposed even to a very moderate degree of friction, and had not undergone subaerial decay before being deposited. Adobe collected, at typical localities is so fine in texture that no grit can be felt when it is rubbed between the fingers; in other instances it contains angular rock fragments of appreciable size.

The composition of the material is illustrated by the following analyses:

ANALYSES OF ADOBE.

BY L. G. EAKINS.

Constituents. No. 1. No. 2. No. 3. No. 4. Sante Fe, New Fort Wingate, Humboldt, Salt Lake Mexico. New Mexico. Nevada. City, Utah. SiO₂ 66.69 26.67 44.64 19.24 Al₂O₃ 14.16 0.91 13.19 3.26 Fe₂O₃ 4.38 0.64 5.12 1.09 MnO 0.09 trace 0.13 trace CaO 2.49 36.40 13.91 38.94 MgO 1.28 0.51 2.96 2.75 K₂O 1.21 trace 1.71 trace Na₂O 0.67 trace 0.59 trace CO₂ 0.77 25.84 8.55 29.57 P₂O₅ 0.29 0.75 0.94 0.23 SO₃ 0.41 0.82 0.64 0.53 Cl 0.34 0.07 0.14 0.11 H₂O 4.94 2.26 3.84 1.67 Organic matter 2.00 5.10 3.43 2.96 ————— ————— ————— —————— 99.72 99.97 99.84 100.35

=51. Vegetable Soils.=—The heavy soils whose origin has been described 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.

First of all, according to this authority, it is necessary to determine the point of view from which the sample is to be taken. If the object is a general study, having for its aim the determination of the general composition of the soils of a definite geologic formation, the sample should be taken in such a way that the different characteristics of the soil alone should enter into consideration without paying any attention to its accidental components, which have been determined by local causes, such as are produced by continued high cultivation, the application of abundant fertilizers, or the practice of a particular line of agriculture. The samples of soil therefore, with such an object in view, should be taken on parts of the earth which are beyond the reach of the causes mentioned above and which tend to modify the nature of the primitive soil. In such a case it is the soil which has not been modified, or better still, virgin soil, such as is found in the woodlands and prairies, which should be taken for a sample, choosing those places in which the geologic formation is most perfectly characterized. In such a case a soil taken in one spot corresponding to the conditions before mentioned, would be the best for the purposes in view. The sample would thus represent a true type to be studied, not one of a mean composition got by taking samples from different localities and mixing them into a homogeneous parcel. This last method of proceeding could introduce into the sample earth modified by culture or by influences purely accidental. However, it would be wise, in a region characterized by the same geologic formation, to take a certain number of samples in different localities, and examine singly each one of them in order to be assured that there is a uniformity of composition in the whole of the soils.

If, on the contrary, it is the purpose of the investigation to furnish information to the cultivator concerning the fields which are worked, it is necessary to approach the problem from a different point of view. In this case the earth which is under cultivation should be first of all considered with all the modifications which nature causes or practical culture has caused, in it. But it often happens that upon the same farm the natural soil is variable, caused either by the washings from the adjacent soils, by the accumulation at certain points of deposits formed from standing water, or from other reasons. In such a case it would be necessary to take samples from every part of the field which exhibited any variation from the general type, in order to get a complete mean sample of the whole. It is necessary to be on guard against making a mixture of these different lots which would neither represent the different soils constituting the farm nor their mean composition. It would be better to examine each of these samples alone and then from those parts which appear to have a similar composition, to take a general sample for the mean analysis.

Most often it is necessary to confine our studies to the really important part of the farm the composition of which would have a practical interest. The aspect of the spontaneous vegetation in such a case, will often serve as a guide to determine the parts of the farms which are similar in nature. The sample should represent the arable layer, properly so-called, that is, that part of it which is stirred by the agricultural implements in use and in which the root system of the plant takes its greatest development and which is the true reservoir of the fertilizing materials.

When a trench is dug in the soil it is easy to distinguish the arable layer from the subsoil. In the first place, its color is different, generally being modified by vegetable débris which forms the supply of humus. The depth of the arable layer is variable, but it is most frequently between 200 and 300 millimeters. In the analysis the depth and layers should be indicated since the chemical composition of the earth varies according as the sample is taken to a greater or less depth. As an example of this it may be said that the quantity of nitrogen decreases in general in proportion as the depth of the layer is increased. The sample, therefore, should be limited exactly to the arable layer of soil.

=61. Caldwell=[44] advises that according to the purpose of the analysis samples be taken:

_a_, from one or from several spots in the field, in order to subject each sample to a separate analysis; or

_b_, for an average representation of the soil of the whole field; in this case, several portions of earth are taken from points distributed in a regular manner over the field, all of which are most carefully mixed together, and 4–6 kilograms of the mixture, free from any large stones, are preserved as the average sample.

An excavation in the soil 30–50 centimeters deep, or through to the subsoil, and 30–50 centimeters square, with one side as nearly vertical as possible is made and a slice taken from this side of uniform thickness throughout, weighing 4–5 kilograms. If the subsoil is to be examined, a sample of it should be taken out in the same manner as directed for the upper soil, to the depth of about 60 centimeters.

If the character of the soil varies materially in different parts of the field, samples from several spots should be analyzed separately.

A small portion of the sample should be put at once in a well-stoppered bottle; the remainder may be allowed to become air-dried, by exposing it in a thin layer, in summer, to the common temperature in the shade, or, in winter, to that of a warm room, or a moderately warm drying-chamber, heated to 30°–40°; in either case it should be carefully protected from dust.

At the time of taking the sample of the soil, observations should be made in regard to the following points:

_a._ The geognostic origin of the soil.

_b._ The nature of the underlying strata, to the depth of 1–2 meters, if practicable.

_c._ The meteorology of the locality, by consulting meteorological records, if possible; otherwise, by the general opinion of the neighborhood; in this connection, the height of the locality above the level of the sea should be noted also.

_d._ The management and rotation of crops in previous years.

_e._ The character of the customary manuring.

_f._ The amount of the crops removed in the preceding year, and, if possible, the average amount of each of the more important crops yielded by the field.

_g._ The practical judgment of neighboring farmers in regard to the field.

Caldwel’s method is practically identical with that of Wolff[45] which was one of the earliest of the systematic schemes for taking soil samples.

=62. Wahnschaffe=[46] insists on rather a fuller preliminary statement to accompany soil samples but gives essentially the method of Wolff with some unimportant variations which add little to the value of the process.

=63. Method Of Peligot.=—According to Peligot[47] the taking of samples of soil of which the physical and chemical properties are to be determined is a delicate operation.

These samples should represent as nearly as possible both the good and bad qualities of a soil.

In the field selected are chosen a certain number of places at least four or five per hectare. The spots selected should have a homogeneous appearance—resembling as nearly as possible the general aspect of the field.

By means of a spade a few kilograms of earth are removed to the depth of the subsoil being careful to include in the sample no accidental detritus which the upper part of the soil especially may contain.

The samples should be taken immediately after the crop is harvested and before any fresh fertilizer is applied. The samples are carefully mixed and placed in a glass bottle or flask.

The sample of subsoil is obtained in the same manner. If the field presents notable differences in surface or fertility all the samples taken should be examined separately.

=64. Method of Whitney.=[48]—An ordinary wood auger, 2½ inches in diameter is so arranged as to admit of additions to the stem to enable the operator to take samples at different depths. It may be fitted with a short piece of gas pipe for a handle and the several pieces of which it is composed may be taken apart and carried in a knapsack.

In taking a soil sample the boring is continued until a change in color shows that the subsoil has been reached. The auger cuts a very clean sample save in excessively sandy soil. After the soil sample is secured the hole is cleaned out and the sample of subsoil taken by the same instrument. The soil is conveniently preserved in heavy cloth bags of which the usual size is 6 by 8½ inches. Where larger samples are required the size of the bag is correspondingly increased. Each bag is to be tagged or labeled to correspond with the entry in the note book.