CHAPTER XXII.. Alkali Soils.

ALKALI SOILS.

Alkali Lands and Seashore Lands.—Alkali lands proper, as already stated, are wholly distinct in their nature and origin from the salty lands of sea-coast marshes, past or present. The latter derive their salts from sea-water that occasionally overflows them, or from that which has evaporated in segregated basins or estuaries; and the salts impregnating them are essentially “sea salts,” that is, common salt, together with bittern (magnesium chlorid), Epsom salt (magnesium sulfate) gypsum, etc. (see chapter 2, p. 26). Very little of what would be useful to vegetation or desirable as a fertilizer is contained in the salts impregnating such soils; and they are by no means always intrinsically rich in plant-food, but vary greatly in this respect.

While seashore lands are by no means always of high fertility even when freed from their salts, especially when very sandy, it is otherwise when they occur near the mouths of streams or rivers, whose finest sediments they then receive. From such lands are formed the profusely productive Polders of Holland and northern Germany, and the equally noted “colmates” of France and Italy. These, so soon as freed from salt, may be considered as possessing the same advantages as “delta” alluvial lands, and from the same causes; notably the accumulation of the finest sediments derived from the rivers’ drainage basins.

Origin.—Alkali lands proper bear no definite relation to the present sea; they are mostly remote from it or from any other sea bed, so that they have sometimes been designated as “terrestrial salt lands.” Their existence is in the majority of cases definitely traceable to climatic conditions alone. They are the natural result of a light rainfall, insufficient to leach out of the land the salts that always form in it by progressive weathering of the rock powder of which all soils largely consist. Where the rainfall is abundant, that portion of the salts corresponding to “sea salts” is leached out into the bottom water, and with this passes through springs and rivulets into the country drainage, to be finally carried to the ocean. Another portion of the salts formed by weathering, however, is partially or wholly retained by the soil; it is that portion chiefly useful as plant food.

See Chapter 2, p. 26.

It follows that when, in consequence of insufficient rainfall, all or most of the salts are retained in the soil, they will contain not only the ingredients of sea-water, but also those useful to plants. In rainy climates a large portion even of the latter is leached out and carried away. In extremely arid climates, on the contrary, the entire mass of the salts remains in the soils; and, being largely soluble in water, evaporation during the dry season brings them to the surface, where they may accumulate to such an extent as to render ordinary useful vegetation impossible; as is seen in “alkali spots,” and sometimes in extensive tracts of “alkali desert.” Three compounds, viz. the sulfate, chlorid and carbonate of sodium, usually form the main mass of these saline efflorescences. Magnesium sulfate (Epsom salt) is in many cases a very abundant ingredient; some calcium sulfate is nearly always present, and calcium chlorid is not infrequently found.

In some cases the above salts are in part at least derived from the leaching of adjacent or subjacent geological deposits impregnated with them at the time of their formation. Such is the case in portions of Wyoming, Colorado and New Mexico, in the Colorado river delta, and in the Hungarian Plain; and it is in these cases especially that the chlorids of calcium and magnesium also form part of the saline mixture.

Geographical Distribution of Alkali Lands.—In looking over a rainfall map of the globe we see that a very considerable portion of the earth’s surface, forming two belts to poleward of the two tropics, has deficient rainfall; the latter term being commonly meant to imply any annual average less than 20 inches (500 millimeters). The arid region thus defined includes, in North America, most of the country lying west of the one hundredth meridian up to the Cascade Mountains, and northward beyond the line of the United States; southward, it reaches far into Mexico, including especially the Mexican plateau. In South America it includes most of the Pacific Slope (Peru and Chile) south to Araucania; and eastward of the Andes, the greater portion of the plains of western Brazil and Argentina. In Europe only a small portion of the Mediterranean border is included; but the entire African coast-belt opposite, with the Saharan and Libyan deserts, Egypt and Arabia, are included therein, as well as, south of the Equator, a considerable portion of South Africa (Kalahari desert). In Asia, Asia Minor, Syria (with Palestine), Mesopotamia, Persia, and northwestern India up to the Ganges, and northward, the great plains or steppes of central Asia eastward to Mongolia and western China, fall into the same category; as does also a large portion of the Australian continent.

See above, chapter 16, p. 294.

Utilization of World-wide Importance.—Over these vast areas alkali lands occur to a greater or less extent, the exceptions being the mountain regions and adjacent lands on the side exposed to the prevailing winds. It will therefore be seen that the problem of the utilization of alkali lands for agriculture is not of local interest only, but is of world-wide importance. It will also be noted that many of the countries referred to are those in which the most ancient civilizations have existed in the past, but which at present, with few exceptions, are occupied by semi-civilized people only. It is doubtless from this cause that the nature of alkali lands has until lately been so little understood, that even their essential distinctness from the sea-border lands has been but recently recognized in full. Moreover, the great intrinsic fertility of these lands when freed from the noxious salts, has been very little appreciated; their repellent aspect causing them to be generally considered as permanently waste lands.

Repellent aspect.—This aspect is essentially due to their natural vegetation being in most cases confined to plants useless to man, commonly designated as “saline vegetation,” of which but little is usually relished by cattle. Notable exceptions to this rule occur in North and South America, Australia, and Africa, where the “saltbushes” of the former and the “karroo” vegetation of the latter form valuable pasture and browsing grounds. Apart from these, however, all efforts to find culture plants for these lands generally acceptable, or at least profitable, in their natural condition, have not been very successful.

See Chapter 23.

Figure 60 illustrates the usual aspect of alkali lands in the San Joaquin valley of California. It will be noted that the alkali-covered surface is only in spots, with clumps of vegetation between, so that cattle can find both pasture and browsing on a portion of such lands, even though the plants so growing are not usually of the most desirable kind. We find in all arid regions, however, considerable areas either wholly destitute of vegetation, or bearing only such saline growth as is rejected by all kinds of domestic animals.

Effects of Alkali upon culture plants.—In land very strongly impregnated with alkali salts, most culture plants, if their seed germinates at all, will show a sickly growth for a short time, “spindle up” and then die without fruiting. In soils less heavily charged the plants may simply become dwarfed, and fruit scantily. The effect on grown trees around which alkali has come up, is first, scanty leafage and short growth of shoots, themselves but sparsely clothed with leaves. This state of things is well shown in figures 61 and 62, which represent apricot trees growing but a short distance apart, but one coming within range of an expanding alkali spot. The characteristic sparseness of the foliage of the “alkalied” tree as compared with the adjacent one is well shown.

Nature of the injury to plants from Alkali.—When we examine plants that have been injured by alkali, we will mostly find that the visible damage has been done near the base of the trunk, or root crown; rarely at any considerable depth in the soil itself. In the case of green herbaceous stems, the bark is found to have been turned to a brownish tinge for half an inch or more, so as to be soft and easily peeled off. In the case of trees, the rough bark is found to be of a dark, almost black, tint, and the green layer underneath has, as in the case of herbaceous stems, been turned brown to a greater or less extent. In either case the plant has been practically “girdled,” the effect being aggravated by the diseased sap poisoning more or less the whole stem and roots. The plant may not die, but it will be quite certain to become unprofitable to the grower.

APRICOT TREES ON ALKALI GROUND.]

It is mainly in the case of land very heavily charged with common salt, as in the marshes bordering the sea, or salt lakes, that injury arises from the direct effects of the salty soil-water upon the feeding roots themselves. In a few cases the gradual rise of salt water from below in consequence of defective drainage, has seriously injured, and even destroyed, old orange orchards. The natural occupancy of the ground by certain native plants may be held to indicate that the soil is too heavily charged with saline ingredients to permit healthy root growth or nutrition until the excess of salts is removed. (See below, chapters 23 and 26).

The fact that in cultivated land the injury is usually found to occur near the surface of the soil, concurrently with the well-known fact that the maximum accumulation of salts at the surface is always found near the end of the dry season, indicates clearly that this accumulation is due to evaporation at the surface. The latter is often found covered with a crust consisting of earth cemented by the crystallized salts, and later in the season with a layer of whitish dust resulting from the drying-out of the crust first formed. It is this dust which becomes so annoying to the inhabitants and travelers in alkali regions, when high winds prevail, irritating the eyes and nostrils and parching the lips.

Effects of Irrigation.—One of the most annoying and discouraging features of the cultivation of lands in alkali regions is that, although in their natural condition they may show but little alkali on their surface, and that mostly in limited spots, these spots are found to enlarge rapidly as irrigation is practiced. Yet since alkali salts are the symptoms and result of insufficient rainfall, irrigation is a necessary condition of agriculture wherever they prevail. Under irrigation, neighboring spots will oftentimes merge together into one large one, and at times the entire area, once highly productive and perhaps covered with valuable plantations of trees or vines, will become incapable of supporting useful growth. This annoying phenomenon is popularly known as “the rise of the alkali” in the western United States, but is equally well known in India and other irrigation regions.

The soil being impregnated with a solution of the alkali salts, and acting like a wick, the salts naturally remain behind on the surface as the water evaporates, the process only stopping when the moisture in the soil is exhausted. We thus not infrequently find that after an unusually heavy rainfall there follows a heavier accumulation of alkali salts at the surface, while a light shower produces no perceptible permanent effect. We are thus taught that, within certain limits, the more water evaporates during the season the heavier will be the rise of the alkali; provided that the water is not so abundant as to leach the salts through the soil and subsoil into the subdrainage.

Leaky Irrigation ditches.—Worst of all, however, is the effect of irrigation ditches laid in sandy lands (such as are naturally predominant in arid regions), without proper provision against seepage. The ditch water then gradually fills up the entire substrata so far as they are permeable, and the water-table rises from below until it reaches nearly to the ditch level; shallowing the subsoil, drowning out the deep roots of all vegetation, and bringing close to the surface the entire mass of alkali salts previously diffused through many feet of substrata.

Surface and Substrata of Alkali Lands.—Aside from the desert proper, in the greater portion of the alkali country “alkali spots.” i. e. ground covered with saline efflorescences and showing little or no vegetation, are interspersed with larger areas apparently free from salts and covered with the ordinary vegetation of the region. A view of such country is given in a plate on a previous page. The alkali spots are usually somewhat depressed below the surrounding lands, and after rains remain covered with water for some time; the water frequently assuming a brown or blackish tint after standing.

When a pointed steel probe is pushed down within such an alkali spot, it will usually be found that, although the soil may appear quite sandy, it is penetrated with some difficulty; while outside of the spots, the probe does not encounter serious resistance until it reaches the depth of two or three feet, when it frequently becomes impossible to penetrate farther without the aid of a hammer. On the margin of the spots, the transition from utter barrenness to a luxuriant vegetation of native weeds is mostly quite sudden; as is shown in the figure, p. 425.

Vertical Distribution of the Salts in Alkali Land.—The results of a comparative examination of such land before and after irrigation, are shown in the annexed diagrams; in which the kind and amount of salts is shown for every three inches of vertical depth, down to four feet, by curves whose extension from left to right indicate the several percentages, while the outer curved line gives the total of salts for each of the several depths.

Fig. 63 represents the condition of the salts in an “alkali spot” as found at the end of the dry season at the Tulare substation, California. The soil was sampled to the depth of two feet at intervals of three inches each. It is easy to see that at this time the bulk of the salts was accumulated within the first six inches from the surface, while lower down the soil contained so little that few culture plants would be hurt by them.

How Native Plants Live.—Fig. 64 represents similarly the state of things in a natural soil alongside of the alkali spot, but in which the native vegetation of brilliant flowers develops annually without any hindrance from alkali. Samples were taken from this spot in March, near the end of the wet, and in September, near the end of the dry season, and each series fully analyzed. There was scarcely a noticeable difference in the results obtained. It is seen in the figure that down to the depth of 15 inches there was practically no alkali found (0.035%), and it was within these 15 inches of soil that the native plants mostly had their roots and developed their annual growth. But from that level downward the alkali rapidly increased, and reached a maximum (0.529%), at about 33 inches; decreasing rapidly thence until, at the end of the fourth foot in depth, there was not more alkali than within the first foot from the surface. In other words, the bulk of the salts had accumulated at the greatest depth to which the annual rainfall (7 inches) ever reaches, forming there a sheet of tough, intractable clay-hardpan. The shallow-rooted native plants germinated their seeds freely on the alkali-free surface; their roots kept above the strongly-charged subsoil, and through them and the stems and foliage all the soil moisture was evaporated by the time the plants died. Thus no alkali was brought up from below by evaporation. The seeds shed would remain uninjured, and would again germinate the coming season.

Hilgard and Loughridge, Bulletin No. 128, California Experiment Station; Report California Experiment Station, 1894-95, p. 37; Bulletin No. 30, Office of Experiment Stations; Wollny’s Forsch. Geb. Agr. Phys., 1896.

Tulare Experiment Substation, California.]

Tulare Experiment Substation, California.]

It is thus that the luxuriant vegetation of the San Joaquin plains, dotted with occasional alkali spots, is maintained; the spots themselves being almost always depressions in which the rain water may gather, and where, in consequence of the increased evaporation, the noxious salts have risen to the surface and render impossible all but the most resistant saline growth; particularly when, in consequence of maceration and fermentation in the soil, the formation of carbonate of soda has caused the surface to sink and become almost water-tight.

Upward Translocation from Irrigation.—Fig. 65 shows the corresponding profile of the same soil after several years’ irrigation. The upward movement of the salts is clearly seen by comparison with the previous figure; and the surface soil has become so charged with salts that the seeds of culture plants refuse to germinate.

Ten feet from this bare alkali ground, on which barley had refused to grow, a crop of barley four feet high was harvested the same year, without irrigation. Investigation proved that here the condition of the soil was intermediate between the two preceding diagrams. The irrigation water had dissolved the alkali of the subsoil, and the more abundant evaporation had brought it nearer the surface; but the shading by the barley crop and the evaporation of the moisture through its roots and leaves had prevented the salts from reaching the surface in such amounts as to injure the crop, although the tendency to rise was clearly shown. By the use of gypsum, moreover, the injuriousness of the alkali had been somewhat diminished.

The same season, grain crops were almost a failure on alkali-free land in the same region; and in connection with this result it should be noted as a general fact that alkali lands always retain a certain amount of moisture perceptible to the hand during the dry season, and that this moisture can be utilized by crops; so that at times when crops fail on non-alkaline land, good ones are obtained where a slight taint of alkali exists in the soil. Actual determinations showed that while a sample of alkali soil containing .54% of salts absorbed 12.3% of moisture from moist air, the same soil when leached absorbed only 2.5%—a figure corresponding to that of sandy upland loams.

Tulare Experiment Substation, California.]

Alkali in Sandy Lands.—In very sandy lands, and particularly when the alkali is “white” only, the tendency to accumulation near the surface is much less, even under irrigation. In the natural condition the salts are in such cases often found quite evenly distributed through soil columns of four feet, and even more. This is an additional cause of the lesser injuriousness of “white alkali.” An illustration of the distribution of the salts in very sandy lands, from the Tulare substation, is given in Fig. 66. Here we see that the maximum is not at, but some distance below the surface, the entire saline mass is lower down than in the more clayey loam of the same locality, and is more widely distributed in depth.

Distribution of Alkali Salts in Heavy Lands.—The mode of distribution of alkali salts in the heavier, close-grained soil of the Chino experimental tract in southern California, is illustrated in Fig. 67. This land is permanently moist, from a water-table ranging from five to seven feet below the surface in ordinary years. There is therefore no opportunity for the formation of “alkali hardpan” as in the case of the Tulare soil; the salts always remain rather near the surface, viz. within twelve to fifteen inches. But being in much smaller average amounts than at Tulare (an average of about 5300 lbs. per acre), quite a copious natural vegetation of grasses, sunflowers, and “yerba mansa” covered the whole surface, save in a few low spots.

A similar mode of distribution of the salts is found in the still more clayey “black adobe” lands of the Great Valley of California. The scanty rains cannot penetrate these soils to any great depth, so that evaporation will soon bring the salts carried by them back to within a short distance of the surface. Their accumulation there is frequently indicated by the entire absence of any but the most resistant alkali weeds, even though the total of salts in the land may not be very great.

Salton Basin.—A peculiar state of things is illustrated in the Salton Basin, which represents what was at one time the head of the Gulf of California, and at the lowest point of which, 268 feet below sea level, there now lies a large deposit of rock salt. It has been cut off from the present Gulf by the delta deposits of the Colorado river, which now, however, overflows into the Basin at times of extreme high water. Although appearing level to the eye, the general slope of the country is to the lowest point of the former sea-bottom.

The region, now in progress of settlement by means of irrigation water brought from the river near Yuma, was investigated with respect to its alkali conditions in 1900 (Bulletin No. 140, Calif. Agric. Expt. Sta.). The annexed diagram 68 shows the distribution of the salts to a depth of 21 feet. It will be noted that here also the alkali content becomes insignificant at 4 feet depth, but increases again to a second maximum at about 15 feet, below which there is a second decrease; below this, at 20 feet, there is a final very heavy increase, not only of the total salts but especially of common salt, which evidently represents the drainage toward the salt deposit. Above this level there is a very remarkable predominance of Glauber’s salt (sodium sulfate), also observable elsewhere, e. g. near White Plains, Nev., whose name is derived from the copious surface accumulation of the sulfate. It seems as though this must have been formed in some way from the common salt.

Horizontal Distribution of Alkali Salts in Arid Lands.—The constant occurrence of “alkali spots” in arid lands shows at once the great inequality of horizontal distribution of alkali impregnation. This is as prominent in level lands as on slopes, and in extremely arid regions it is mostly not possible to recognize even very considerable differences without close examination. Thus in lands appearing exactly alike on the surface, on the edge of the Salton basin in California, on the same forty acre 1.4% (56,000 pounds per acre) was found in the surface four feet at one point, and a hundred yards away, 12.5% (500,000 pounds). The mapping of alkali lands is therefore somewhat precarious unless carried into great detail. Moreover, it has been found that the location of the salts changes from year to year, especially in irrigated land, as might be expected. Those cultivating alkali lands have therefore to exercise constant watchfulness, unless the salts have been definitively eliminated by underdrainage over a considerable area; as merely local operations may be rendered ineffectual by the migration of the salts from neighboring tracts not reclaimed.

Alkali in Hill Lands.—As a rule, hill lands themselves are remarkably free from alkali, even in the arid regions; except when water is gathered in depressions, where strongly saline waters may be found in Washington, Montana and elsewhere. But on level plateau lands, where drainage is slow or imperfect, alkali appears as freely as it does in the same regions in the stream bottoms. In the latter the leachings and seepage of the uplands naturally causes a concentration of the salts, and thus we find alkali salts incrusting the surface in the valleys of the streams, as e. g., that of the Yellowstone, Musselshell, Judith, Yakima and others in the north, and of Green river, Platte, Pecos, and Rio Grande farther south; as well as in numerous valleys of central and southern California.

Usar Lands of India.—These lands have been investigated first by the “Reh Commission” appointed to investigate the causes of the deterioration of lands in the Aligarh district (south of Delhi, between the Ganges and Jumna rivers), in 1876. The occasion of this appointment was the appearance of “reh” (alkali salts) in a region which had previously been free from them. Subsequently, a more elaborate investigation of the subject was made by Dr. J. W. Leather, Agricultural Chemist to the Government of India. From these documents it appears that “usar lands” exist largely not only in the Northwestern Provinces and Oudh, but also in the Panjab, especially on the lands bordering the Chenab river; likewise to a slight extent in the Bombay presidency. Leather’s investigation shows that not all the lands designated by the natives as usar contain soluble salts in injurious amounts, some being simply lands having very hard, clayey soils difficult to till with the imperfect methods employed. Yet the general phenomena of the true “reh” lands are practically identical with those of the American alkali lands, including also the calcareous hardpan, there called kankar. Owing probably to the long cultivation of the Indian lands (mostly under irrigation), the salts are there at their maximum in the first foot, decreasing as depth increases. It is noteworthy also that in the majority of cases the predominant salt is carbonate of soda or black alkali, which there as in California renders the lands impervious to water until treated with gypsum. This fact accounts for the popular use of the same name for non-saline impervious clay soils, and the alkali or reh lands proper.

We have an entirely analogous case in the “Szek” lands of the Hungarian plain, some of which are simply poor refractory soils containing a trace of soluble salts; while lower down in the valley of the Theiss we find genuine alkali lands, both black and white, which have long furnished carbonate of soda for local use and commerce. In this case, however, the alkali salts seen to come largely, in some cases wholly, from underlying saline clays whose salts in coming to the surface suffer precisely the same transformations experienced in California and India, in presence of calcic carbonate (see below, p. 450 ff).

An abstract of the report of this commission is given in the Report of the California Experiment Station for 1890.

See Agricultural Ledger, 1897, No. 13; ibid. 1901, No. 13.

The accounts given by v. Middendorff of the nature and occurrence of alkali lands in Turkestan (Ferghana) agree entirely with those given above for California and India; as do also the investigations made by other Russian observers on the saline lands of the steppes of European Russia.

COMPOSITION AND QUANTITY OF ALKALI SALTS.

Black and White Alkali.—Broadly speaking, the world over alkali salts consist mainly of three chief ingredients, already mentioned, namely, common salt, Glauber’s salt (sulfate of soda), and salsoda or carbonate of soda. The latter causes what is popularly known as “black alkali,” from the black spots of puddles seen on the surface of lands tainted with it, owing to the dissolution of the soil humus; while the other salts, often together with Epsom salt and bittern (Magnesium chlorid), constitute “white alkali,” which is known to be very much milder in its effect on plants than the black. In most cases all three are present, and all may be considered as practically valueless, or noxious, to plant growth.

In this designation are included, in this volume, both the normal (mono-) carbonate and the two other compounds, the bi- or hydrocarbonate and the intermediate (so-called sesqui-) compound or trona; all of which are commonly present simultaneously, but in utterly indefinite relative proportions, varying from day to day and from inch to inch of depth, inasmuch as their continued existence depends upon the greater or less formation of carbonic acid in the soil, and the access of air. Hence their separate quantitative determination at any one time is of little practical interest. All naturally occurring carbonate of soda contains, and sometimes consists of, these “super-carbonates,” according to the greater or less exposure to air and solar heat. They are much milder in their action on plants than the monocarbonate, which unfortunately, in the nature of the case, always predominates near the surface, and thus injures the root-crown.

A wholly different kind of “black alkali” exists in some regions, especially in the delta lands of the Colorado of the West and in the Pecos and Rio Grande country in New Mexico. In these cases the dark tint is due, not to a humic solution, but simply to moisture, which is tenaciously retained by the chlorids of calcium and magnesium impregnating the land, thus contrasting strongly with the gray tint of the general dry soil.

=========================+=================+========================= | EUROPE. | ASIA. |-----------------+-----------------+------- | HUNGARIAN | ARALO-CASPIAN | ADEN. | PLAIN. | PLAIN. |“HURKA” | “SZEKSO.” | SALINE CRUSTS.|“KARA.” +---------+-------+ | |Debreczin|Kalocsa| | | | | | | | | | -------------------------+---------+-------+-----+-----+-----+------- | | | | | | Potassium Sulfate (K₂SO₄)| | | | | | Sodium Sulfate (Na₂SO₄) | .2 | 1.6| 10.4| 18.2| 15.5| Sodium Carbonate (Na₂CO₃)| 48.1 | 92.5| 14.7| 12.1| 69.0| 67.2 Sodium Chlorid (NaCl) | 51.7 | 4.4| 74.6| 69.7| 15.5| 32.8 Sodium Phosphate (Na₃PO₄)| | 1.5| | | | Calcium Chlorid | | | | | | Magnesium Chlorid (MgCl₂)| | | | | | +---------+-------+-----+-----+-----+------- | 100.0 | 100.0|100.0|100.0|100.0| 100.0 -------------------------+---------+-------+-----+-----+-----+-------

=========================+====================================== | ASIA. |-------------------------------------- | INDIA | “REH.” +-------------------------------------- | |Gursikar,|Jellalabad,|Bayamati | |Aligarh, |Panjab, |(Regur), | |6 feet. |1.5 feet. |Deccan, | | | |2 feet. -------------------------+-------+---------+-----------+-------- | | | | Potassium Sulfate (K₂SO₄)| 11.1 | | | Sodium Sulfate (Na₂SO₄) | 7.0 | 15.5 | 58.5 | 2.3 Sodium Carbonate (Na₂CO₃)| 79.0 | 56.9 | 22.9 | Sodium Chlorid (NaCl) | 2.9 | 27.6 | 18.6 | 97.7 Sodium Phosphate (Na₃PO₄)| | | | Calcium Chlorid | | | | Magnesium Chlorid (MgCl₂)| | | | +-------+---------+-----------+-------- | 100.0 | 100.0 | 100.0 | 100.0 -------------------------+-------+---------+-----------+--------

=========================+====================================== | AFRICA. +--------------------------+------------- | EGYPT. | | | +---------------+----------+ | Trona, | Alkali | Fezzan | (Commercial.) |L. Abukir.| Trona, | | |(Commercial.) | | | -------------------------+------+--------+----------+------------- | | | | Potassium Sulfate (K₂SO₄)| | | 6.49 | Sodium Sulfate (Na₂SO₄) | 23.6 | 38.3 | .82 | 0.6 Sodium Carbonate (Na₂CO₃)| 28.2 | 47.7 | 1.13 | 98.7 Sodium Chlorid (NaCl) | 48.2 | 14.0 | 89.74 | .7 Sodium Phosphate (Na₃PO₄)| | | | Calcium Chlorid | | | 1.82 | Magnesium Chlorid (MgCl₂)| | | | +------+--------+----------+------------- |100.0 | 100.0 | 100.00 | 100.0 -------------------------+------+--------+----------+-------------

===========================+======================================== | CALIFORNIA. +------+---------+----------------+------ | | | Tulare County. | |Merced|Overhiser+-------+--------+ Kern |Falls.| San |Visalia| Expt. |Island | | Joaquin | |Station.| | | Co. | |Tulare. | ---------------------------+------+---------+-------+--------+------ Potassium Chlorid, KCl | | | | | Potassium Sulfate, K₂SO₄ | | 20.23 | 3.95| 10.13| Potassium Carbonate. K₂CO₃ | | | | | Sodium Sulfate, Na₂SO₄ | 4.67| 13.00 | | 25.28| 88.42 Sodium Nitrate, NaNO₃ | 12.98| | | 19.78| Sodium Carbonate, Na₂CO₃ | 75.95| 52.22 | 65.72| 32.58| 0.42 Sodium Chlorid, (NaCl) | 1.46| 33.00 | 3.98| 14.75| 0.51 Sodium Phosphate, HNa₂PO₄ | 4.94| 1.78 | 8.42| 2.25| Magnesium Sulfate, MgSO₄ | | | 1.65| | 0.52 Calcium Chlorid | | | | | Magnesium Chlorid | | | | | Ammonium Carbonate, NH₄CO₃ | | | | 1.41| ---------------------------+------+---------+-------+--------+------ |100.00| 100.00 | 100.00| 100.00|100.00 ---------------------------+------+---------+-------+--------+------

===========================+======================================== | CALIFORNIA. +-------+----------+-----------+--------- | | | | | Mojave| Hunts, |Westminster| Imperial |Plateau| near | near | | | San | Santa Ana.| | |Bernardino| | ---------------------------+-------+----------+-----------+--------- Potassium Chlorid, KCl | | | | 1.15 Potassium Sulfate, K₂SO₄ | 0.92 | 5.31 | 20.62 | Potassium Carbonate. K₂CO₃ | | | 6.59 | Sodium Sulfate, Na₂SO₄ | 43.34 | 66.08 | | Sodium Nitrate, NaNO₃ | | | | 8.21 Sodium Carbonate, Na₂CO₃ | 15.38 | 15.85 | 62.22 | .58 Sodium Chlorid, (NaCl) | 39.34 | 11.47 | 10.57 | 31.82 Sodium Phosphate, HNa₂PO₄ | 1.02 | | | Magnesium Sulfate, MgSO₄ | | 0.59 | | Calcium Chlorid | | | | 58.42 Magnesium Chlorid | | | | 2.81 Ammonium Carbonate, NH₄CO₃ | | | | ---------------------------+-------+----------+-----------+--------- |100.00 | 100.00 | 100.00 | 100.00 ---------------------------+-------+----------+-----------+---------

=======================+==================================== | WASHINGTON. +--------+--------+--------+---------- | Yakima| | | Spokane | Co. |Kittitas| Whitman| Co., | on |Valley. | Co., |Cottonwood | Atahnam| | Lake | Springs. | Creek.| | Creek. | ---------------------------+--------+--------+--------+---------- Potassium Chlorid, KCl | 3.90 | 0.16 | 4.53 | 6.27 Potassium Sulfate, K₂SO₄ | 18.44 | 15.17 | 15.90 | Potassium Carbonate. K₂CO₃ | | | | Sodium Sulfate, Na₂SO₄ | | | | Sodium Nitrate, NaNO₃ | 75.61 | 80.36 | 77.10 | 87.14 Sodium Carbonate, Na₂CO₃ | 0.52 | 1.76 | 1.34 | 4.03 Sodium Chlorid, (NaCl) | 1.53 | 2.55 | 1.13 | 2.56 Sodium Phosphate, HNa₂PO₄ | | | | Magnesium Sulfate, MgSO₄ | | | | Calcium Chlorid | | | | Magnesium Chlorid | | | | Ammonium Carbonate, NH₄CO₃ | | | | ---------------------------+--------+--------+--------+---------- | 100.00 | 100.00 | 100.00 | 100.00 ---------------------------+--------+--------+--------+----------

========================+=========================================== | MONTANA. ------------------------+------------------------------------------- | UPPER MISSOURI VALLEY. +-----------+-------+------+-------+-------- | Upper |Prickly| Ford | Fort |Robert’s | Missouri | Pear | on |Benton.| Creek, | Valley |Plain. | Sun | | Mussel- | near |Helena.|River.| | shell |Centerville| | | | Valley. ------------------------+-----------+-------+------+-------+-------- | | | | | Potassium Sulfate, K₂SO₄| 2.37 | 3.07| 1.77| 8.59| 3.07 Sodium Sulfate, Na₂SO₄ | 56.54 | 43.38| 83.35| 47.10| 76.79 Sodium Nitrate, NaNO₃ | 9.39 | | | | Sodium Carbonate, Na₂CO₃| | | | .71| 13.99 Sodium Chlorid, NaCl | 27.47 | 14.60| 0.91| .18| 6.15 Magnesium Sulfate, MgSO₄| 4.23 | 38.94| 13.97| 43.42| Potassium Chlorid, KCl | | | | | +-----------+-------+------+-------+-------- | 100.00 | 100.00|100.00| 100.00| 100.00 ------------------------+-----------+-------+------+-------+-------- ========================+============================== | NEVADA. |--------------------+--------- | | | NEAR RENO. | Churchill | | County. ------------------------+----------+---------+--------- | | | Potassium Sulfate, K₂SO₄| | | Sodium Sulfate, Na₂SO₄ | 52.15 | 80.30 | 0.55 Sodium Nitrate, NaNO₃ | | | Sodium Carbonate, Na₂CO₃| 45.37 | 15.24 | 96.78 Sodium Chlorid, NaCl | 2.48 | 4.46 | 2.67 Magnesium Sulfate, MgSO₄| | | Potassium Chlorid, KCl | | | +----------+---------+--------- | 100.00 | 100.00 | 100.00 ------------------------+----------+---------+-------- ========================+========================================= | WYOMING. |----------------------+------------------ | SWEET WATER | LARAMIE FARM. | VALLEY. | |-------------+--------+-------+---------- |Independence,| Saint |Alkali.| Waste | Rock | Mary’s | |Irrigation | Lake. |Station.| | Water. ------------------------+-------------+--------+-------+---------- | | | | Potassium Sulfate, K₂SO₄| | | | Sodium Sulfate, Na₂SO₄ | 73.17 | 88.93 | 59.29| 41.19 Sodium Nitrate, NaNO₃ | | | | Sodium Carbonate, Na₂CO₃| 22.98 | | | Sodium Chlorid, NaCl | 3.85 | 11.63 | 17.01| 2.18 Magnesium Sulfate, MgSO₄| | | 23.70| 43.82 Potassium Chlorid, KCl | | | | 12.81 +-------------+--------+-------+---------- | 100.00 | 100.00 | 100.00| 100.00 ------------------------+-------------+--------+-------+----------

========================+========================================= | COLORADO. +------------+---------+--------+------- | Near | Grand | Rocky | Rocky | Denver. |Junction.| Ford. | Ford. ------------------------+------------+---------+--------+------- Potassium Sulfate, K₂SO₄| | | 0.10 | 13.74 Sodium Sulfate, Na₂SO₄ | 93.40 | 56.05 | 62.54 | 17.36 Sodium Carbonate, Na₂CO₃| | 18.97 | 2.08 | 5.53 Sodium Chlorid, NaCl | 6.60 | 24.98 | 3.86 | 11.53 Magnesium Sulfate, MgSO₄| | | 31.42 | 44.43 Magnesium Chlorid, MgCl₂| | | | 5.76 Magnesium Phosphate | | | | 1.65 +------------+---------+--------+------- | 100.00 | 100.00 | 100.00 | 100.00 ------------------------+------------+---------+--------+-------

========================+========================================= | NEW MEXICO. +------------------------------------------- | PECOS VALLEY. |------------------------+------------------ | ROSWELL REGION. | CARLSBAD REGION. +-------+--------+-------+--------+--------- |Bremond|Michelet|Roswell|Carlsbad|Delaware | | | | | River ------------------------+-------+--------+-------+--------+--------- Potassium Sulfate, K₂SO₄| | | | | Sodium Sulfate, Na₂SO₄ | 54.61 | 2.62 | 67.46 | 35.16 | 37.11 Sodium Carbonate, Na₂CO₃| | | | | Sodium Chlorid, NaCl | 51.60 | 65.16 | 10.00 | 26.88 | 34.31 Magnesium Sulfate, MgSO₄| 13.79 | 32.22 | 22.54 | 38.06 | 28.58 Magnesium Chlorid, MgCl₂| | | | | Magnesium Phosphate | | | | | +-------+--------+-------+--------+--------- |100.00 | 100.00 |100.00 | 100.00 | 100.00 ------------------------+-------+--------+-------+--------+---------

Nutritive Salts in Alkali.—With them, however, there are almost always associated, in varying amounts, sulfate of potash, phosphate of soda, and nitrate of soda, representing the three elements—potassium, phosphorus, and nitrogen—upon the presence of which in the soil in available form, the welfare of our crops so essentially depends, and which we aim to supply in fertilizers. The potash salt is usually present to the extent of from 5 to 20 per cent of the total salts; phosphate, from a fraction of one to as much as 4 percent; the nitrate from a fraction of one to as much as 20 percent. In black alkali the nitrate is usually low, the phosphate high; in the white, the reverse is true. Both relations are readily intelligible from a chemical and bacteriological point of view.

Estimation of Total Alkali in Land.—The investigations detailed above having shown that in California at least, outside of the axes of valleys no practically important amount of alkali salts is usually found at a depth exceeding four feet, it became possible to determine approximately the amounts of salts that would have to be dealt with when irrigation and evaporation should bring the entire amount to or near the surface; a necessary prerequisite to the determination of possible cultures. While, as already shown, the salts occur lower down in very sandy lands, yet the diagram on p. 435 shows that even then, an estimate on this basis would not be very wide of the truth. It is at least probable that the same is measurably true of level alkali lands elsewhere, when not underlaid by geological deposits impregnated with salts.

The total amount of these salts ordinarily found in alkali lands (i. e. in such as in the dry season show saline efflorescences on the surface) is from about one tenth of one per cent to as much as three per cent of the weight of the soil, taken to the depth of four feet. The percentage of salts having been determined in samples representing a tract, it becomes easy to calculate, approximately, the total amounts of each salt present per acre, on the basis of the weight of the soil per acre foot. For the soils of the arid region, such weight will usually range from three million five hundred thousand to four million pounds per acre-foot; the latter being the most usual figure, of which it may be conveniently remembered, that forty thousand pounds represent 1 per cent. We are thus enabled to estimate e. g. the amount of gypsum required to neutralize the carbonate of soda in the salts, or the amounts of valuable nutritive ingredients—potash, phosphoric acid and nitrates—present in the land in the water-soluble form.

As has been shown in the preceding discussion, the analysis at the surface foot alone, which has frequently been alone made, gives no definite clew whatever to the total amounts of salts to be controlled. A full estimate is of special importance in enabling us to forecast what culture plants are likely to succeed on a given tract, by reference to the table of “tolerances” given below (chapter 23, page 467).

Composition of Alkali Soils as a Whole.—As may be imagined, the presence of the alkali salts finds expression in the analytical statement of their composition, although not to the extent usually anticipated from their superficial aspect. The table annexed gives the composition of fourteen alkali soils, taken to the depth of one foot, at times when there was no visible accumulation of salts on the surface. The averages of the several ingredients determined are given in the fifteenth column, and a comparison of its figures with those of the general table on page 377 of chapter 20 will show some marked characteristics. We find the average potash-content to be but little less than twice as great as in the general average for the state of California; in the case of lime the ratio is nearly as one to three, in the case of magnesia nearly one to two; in that of phosphoric acid, one to two and a half, of which in the presence of carbonate of soda an unusually large proportion is in a readily soluble, often in the water-soluble, condition (see preceding table).

The usual proportion of soda, of one-fourth to one-half of the amount of potash, is changed to one-half or three-fourths; in the case of the strongest alkali lands soda may equal or even exceed the potash content. As the latter, however, is invariably high to very high, it does not happen as frequently as might be supposed that the soda content exceeds that of potash as shown by the usual method of soil-extraction with water.

That the potash percentage should always be high in alkali lands, is hardly surprising when it is considered that the continued presence of the salts resulting from rock decomposition affords opportunity for the full exercise of the preference with which potash is known to be retained in soils by the formation of complex zeolitic silicates. In most cases the potash-percentage exceeds .75%, and rises as high as 2.0%; as is shown in the table.

COMPOSITION OF ALKALI SOILS AS A WHOLE.

(A) = White Ash, Fresno. (B) = Wire Grass, Visalia. (C) = Plains, Cross Creek, Tulare (D) = Salt Grass, B. V. Slough. =============================+========+========+========+======== | | | | COLLECTION NUMBER. | (A) | (B) | (C) | (D) | —704— | —585— | —573— | —700— -----------------------------+--------+--------+--------+-------- Coarse Materials > 0.55 mm | |14.29 | 1.50 | Fine Earth | |85.71 |98.50 | | | | | CHEMICAL ANALYSIS OF | | | | FINE EARTH. | | | | -----------------------------+--------+--------+--------+--------- Insoluble matter |85.87 |66.47 |66.08 |87.06 | 88.58| 71.42| 69.46| 89.04 Soluble silica | 2.71 | 4.95 | 3.38 | 1.98 -----------------------------+--------+--------+--------+-------- Potash (K₂O) | .34 | 1.22 | 1.82 | .49 Soda (Na₂O) | .25 | .68 | .44 | .35 Lime (CaO) | 1.16 | 3.04 | 4.31 | 1.20 Magnesia (MgO) | .50 | .09 | 1.59 | 1.07 Bro. ox. of Manganese (Mn₃O₄)| .03 | .03 | .08 | .03 Peroxid of Iron (Fe₂O₃) | 3.28 | 5.82 | 6.04 | 5.82 Alumina (Al₂O₃) | 3.22 | 7.14 | 8.69 | .17 Phosphoric acid (P₂O₅) | .10 | .24 | .74 | .08 Sulfuric acid (SO₃) | .12 | .66 | .26 | .13 Carbonic acid (CO₂) | | 2.55 | 2.53 | Water and organic matter | 1.79 | 7.09 | 4.15 | 1.13 +--------+--------+--------+-------- Total |99.37 |99.97 |99.51 |99.51 +--------+--------+--------+-------- Chlorin, per cent. | | | | Humus | .60 | 1.00 | 1.00 | .17 “ Ash | .35 | .84 | .74 | .20 +--------+--------+--------+-------- “ Nitrogen, per cent. | | | | in Humus |18.66 |14.10 | | +--------+--------+--------+-------- “ “ , per cent. | | | | in soil | .11 | .15 | | +--------+--------+--------+-------- Hygroscopic Moisture | 2.22 | 8.53 | 8.74 | 2.16 absorbed at °C | | | 14° | 15° -----------------------------+--------+--------+--------+-------- | Tulare Lake Alluvium, | Tulare County. COLLECTION NUMBER. | —891— —893— —77— -----------------------------+-----------+----------+------- Coarse Materials > 0.55 mm | | | 4.10 Fine Earth | all | all | 95.90 | | | CHEMICAL ANALYSIS OF | | | FINE EARTH. | | | -----------------------------+-----------+----------+------- Insoluble matter | 54.71 | 56.92 | 67.34 | 64.55| 67.15| Soluble silica | 9.84 | 10.13 | -----------------------------+-----------+----------+------- Potash (K₂O) | 2.02 | 1.65 | 1.05 Soda (Na₂O) | 2.73 | .54 | .84 Lime (CaO) | 2.46 | 2.96 | 6.51 Magnesia (MgO) | 2.93 | 3.12 | 3.69 Bro. ox. of Manganese (Mn₃O₄)| .03 | .04 | .04 Peroxid of Iron (Fe₂O₃) | 7.46 | 6.73 | 5.05 Alumina (Al₂O₃) | 11.50 | 10.35 | 7.97 Phosphoric acid (P₂O₅) | .11 | .16 | .32 Sulfuric acid (SO₃) | .01 | .01 | .08 Carbonic acid (CO₂) | 1.81 | .93 | 4.42 Water and organic matter | 4.34 | 5.77 | 3.71 +-----------+----------+------- Total | 99.95 | 99.92 | 101.29 +-----------+----------+------- Chlorin, per cent. | | | Humus | | .88 | .47 “ Ash | | 1.03 | 2.18 +-----------+----------+------- “ Nitrogen, per cent. | | | in Humus | | | 9.37 +-----------+----------+------- “ “ , per cent. | | | in soil | | | .05 +-----------+----------+------- Hygroscopic Moisture | 10.50 | 8.6 | absorbed at °C | 10° | 10° | -----------------------------+-----------+----------+-------

COMPOSITION OF ALKALI SOILS AS A WHOLE. ============================+==========+===============+============ | Tulare |Ten-acre tract.|Carisa Plain COLLECTION NUMBER |Substation|Chino, S.B. Co.| S.L. Obispo | | | | —1159— | —1284— | —1423— ----------------------------+----------+---------------+------------ Coarse Materials > 0.55mm. | 1.96 | 1.00 | 9.00 Fine Earth. | 98.04 | 99.00 | 91.00 | | | CHEMICAL ANALYSIS OF | | | FINE EARTH. | | | ----------------------------+----------+---------------+------------ Insoluble matter | 72.98 | 62.62 | 57.33 | 73.58| 70.92 | 69.48 Soluble silica | 6.60 | 18.30 | 12.15 ----------------------------+----------+---------------+------------ Potash (K₂O) | 1.20 | .95 | 1.23 Soda (Na₂O) | .52 | .50 | .77 Lime (CaO) | 1.86 | 5.07 | 4.46 Magnesia (MgO) | 1.81 | .84 | 3.12 Br. ox. of Manganese (Mn₃O₄)| .08 | .06 | .01 Peroxid of Iron (Fe₂O₃) | 6.86 | 6.43 | 7.65 Alumina (Al₂O₃) | 5.66 | 4.88 | 6.16 Phosphoric acid (P₂O₅) | .10 | .21 | .43 Sulfuric acid (SO₃) | .03 | .06 | .06 Carbonic acid (CO₂) | | 3.76 | Water and organic matter | 2.54 | 1.02 | 2.63 Total | 100.24 | 99.70 | 99.99 +----------+---------------+------------ Chlorin, per cent | | .12 | Humus, per cent | .37 | 1.99 | 1.39 “ Ash, per cent | .32 | 1.13 | .95 +----------+---------------+------------ “ Nitrogen, per cent. | | | in Humus | 16.75 | 10.20 | 14.36 “ “ , per cent. | | | in soil | .06 | .20 | .06 +----------+---------------+------------ Hygroscopic Moisture | | 5.81 | 8.46 absorbed at °C | | 15° | 15° ----------------------------+----------+-----------+---+------------ | Perris Valley, |Sand, Coachella, COLLECTION NUMBER |Jacinto river, Jacinto| Riverside | Plain, Riverside Co. | Co. | —1758— | —1760— | —2471— ----------------------------+-----------+----------+---------------- Coarse Materials > 0.55mm. | 7.50 | 3.50 | Fine Earth. | 92.50 | 96.50 | all | | | CHEMICAL ANALYSIS OF | | | FINE EARTH. | | | ----------------------------+-----------+----------+---------------- Insoluble matter | 41.59 | 35.20 | 58.95 | 63.13 | 58.95| 77.54 Soluble silica | 21.54 | 23.75 | 11.37 ----------------------------+-----------+----------+---------------- Potash (K₂O) | 1.37 | 1.16 | 1.26 Soda (Na₂O) | 1.97 | .96 | .37 Lime (CaO) | 4.23 | 8.00 | 2.71 Magnesia (MgO) | 3.80 | 5.69 | 2.20 Br. ox. of Manganese (Mn₃O₄)| .03 | .04 | .05 Peroxid of Iron (Fe₂O₃) | 9.65 | 7.33 | 6.43 Alumina (Al₂O₃) | 7.26 | 6.29 | 5.53 Phosphoric acid (P₂O₅) | .23 | .28 | .21 Sulfuric acid (SO₃) | .34 | .21 | .08 Carbonic acid (CO₂) | 4.19 | 6.49 | 1.05 Water and organic matter | 2.89 | 4.71 | 2.55 Total | 99.81 | 99.84 | 99.98 +-----------+----------+---------------- Chlorin, per cent | | Trace. | Humus, per cent | .60 | .91 | .46 “ Ash, per cent | .92 | 1.75 | .42 +-----------+----------+---------------- “ Nitrogen, per cent. | | | in Humus | 6.66 | 7.70 | “ “ , per cent. | | | in soil | .04 | .07 | +-----------+----------+---------------- Hygroscopic Moisture | 9.43 | 8.85 | 2.64 absorbed at °C | 15° | 15° | 15° ----------------------------+-----------+----------+----------------

============================+===============+=========== |Silt, Imperial,|Average of COLLECTION NUMBER | S. Diego Co. | soils. | —2325— | ----------------------------+---------------+----------- Coarse Materials > 0.55mm. | | Fine Earth. | all | | | CHEMICAL ANALYSIS OF | | FINE EARTH. | | ----------------------------+---------------+----------- Insoluble matter | 62.67 | 63.08 | 73.60 | 72.19 Soluble silica | 10.93 | 9.11 ----------------------------+---------------+----------- Potash (K₂O) | .74 | 1.17 Soda (Na₂O) | .29 | .78 Lime (CaO) | 3.75 | 3.71 Magnesia (MgO) | 1.68 | 2.29 Br. ox. of Manganese (Mn₃O₄)| .01 | .04 Peroxid of Iron (Fe₂O₃) | 3.71 | 6.30 Alumina (Al₂O₃) | 4.26 | 6.65 Phosphoric acid (P₂O₅) | .22 | .20 Sulfuric acid (SO₃) | .36 | .17 Carbonic acid (CO₂) | 2.32 | 2.14 Water and organic matter | 8.93 | 4.19 Total | 99.87 | +---------------+----------- Chlorin, per cent | | Humus, per cent | .65 | .75 “ Ash, per cent | .69 | .82 +---------------+----------- “ Nitrogen, per cent. | | in Humus | 10.90 | “ “ , per cent. | | in soil | .07 | +---------------+----------- Hygroscopic Moisture | 2.98 | 5.63 absorbed at °C | 15° | 15° ----------------------------+---------------+-----------

This table exhibits also another standing characteristic of alkali soils, which is to be anticipated from the conditions of their formation; viz, high lime-content, which sometimes rises to the extent of marliness.

In phosphates, also, alkali soils are almost always high; and an unusually large proportion is found to be readily soluble.

In presence of much carbonate of soda, nitrates are usually scarce or altogether absent; while owing to the action of the alkaline solution upon the humus, ammonia salts, or even free (or carbonated and therefore readily dissociated and assimilated) ammonia may be present, so as to be perceptible to the senses by its odor in hot sunshine. But in the case of “white alkali,” more especially of the sulphate in moderate amounts, nitrification is exceedingly active and nitrates may sometimes rise to as much as 20% of the soluble salts. As alkali spots are usually low in the central portion and therefore more moist than around the edges, we sometimes find ammonia salts in the middle of a spot, while nitrates are abundant along the margin of the same. These differences, first demonstrated by an investigation made by Colmore, illustrate some of the reactions that are essentially concerned in the agricultural availability of alkali lands. A summary of Colmore’s results is given in the table below.

Report of the California Exp’t. St’n. for 1892-94, p. 141.

Cross Section of an Alkali Spot.—The spot examined lies outside of Tulare, California, substation; it being late in the season, when the bulk of the salts is found near the surface, the samples were taken to the depth of one foot only, at points four feet apart, from the center out.

AMOUNT AND COMPOSITION OF SALTS IN ALKALI SPOT FROM CENTER TO CIRCUMFERENCE. 4 FEET APART, 1 FT. DEPTH. ======================+========+========+========+========+======== | 1 | 2 | 3 | 4 | 5 Mineral Salts. | Center | Four | Eight | Twelve | Outer |of spot.| feet. | feet. | feet. | margin. ----------------------+--------+--------+--------+--------+-------- Potassium sulfate | 6.70 | 9.55 | 11.92 | 19.26 | 13.95 Sodium sulfate | 19.84 | 12.85 | 23.72 | 23.97 | 16.96 Magnesium sulfate | 3.07 | .07 | .95 | 2.05 | 8.29 Sodium chlorid | 13.80 | 23.73 | 24.12 | 24.23 | 29.69 Sodium carbonate | 50.72 | 50.96 | 37.55 | 35.49 | 29.94 Sodium phosphate | 5.57 | 2.88 | .87 | ? | 1.04 Sodium nitrate | .30 | ? | .87 | ? | .13 | ------ | ------ | ------ | ------ | ------ Totals | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | | | | | Organic matter | 30.00 | 24.80 | 19.48 | 23.36 | 20.31 Total soluble in soil | .78 | .54 | .70 | .37 | .34 Mineral salts | .38 | .40 | .54 | .25 | .23 ----------------------+--------+--------+--------+--------+--------

While the table shows an obvious irregularity in some of the data at the eight-foot point, arising doubtless from an irregularity of surface or of texture overlooked in taking the samples, we find a very remarkable regularity of progression in the cases of potassium sulfate, sodium chlorid, sodium carbonate and sodium phosphate in the other four samples. The maxima of the “black alkali” and the soluble organic matter (humus) coincide, as does that of the phosphate; the total mineral salts at the outer margin are only a little over half of what is found at the center. This is natural, as owing to the deflocculating effect of the black alkali, the center is nearly a foot lower than the margin. The lowering of the nitrate-content at the outer margin is obviously due to the luxuriant vegetation growing adjacent.

Reactions between the Carbonates, Chlorids and Sulfates of Alkalies and Earths. That a soluble earth-salt, such as the sulfate or chlorid of calcium, will react upon an alkaline carbonate solution so as to form an alkali sulfate, and e.g. lime carbonate, is well known; the neutralization of the sodic carbonate in the soil by means of gypsum, above referred to, is based upon this reaction. It is not so well known that the latter may be reversed, partly or wholly, by the presence of carbonic acid in the solution of the soil. Although observed as early as 1824 by Brandes, and again in 1859 by A. Müller, this reaction is not mentioned in text-books and attracted no attention as a source of naturally occurring alkali carbonates which in the past have formed the basis of extensive commerce from the Orient, until in 1888, the writer together with Weber and later with Jaffa, investigated it quantitatively. It was found that up to .75 grms. per liter, the entire amount of sodic sulfate present in solution is transformed into carbonate in presence of calcic carbonate, by a current of carbonic dioxid; but the amount so transformed does not continue to increase beyond about 4 grams per liter. A corresponding amount of calcic sulfate is formed. In the case of potassic sulfate, the transformation also occurs, proportionally to the molecular weight. This relation is shown in the subjoined diagram, which also shows in the curves on the left, the residual alkalinity left after evaporation and drying the residue at 100° C.

Proc. Am. Soc. Agr. Sci., 1888; ibid., 1890; Rep. Cal. Expt. Sta., 1890, p. 100; Ber. Berlin, Chem. Ges., 1893; Am. Jour. Sci., August 1896.

The corresponding reaction occurs also, of course, between sodium chlorid and calcium carbonate, but not to the same extent, because unlike the difficultly soluble gypsum, the reaction product is the very soluble calcium chlorid, the presence of which in the solution limits the reaction much sooner than when most of the decomposition product is thrown down in the solid state. The calcium chlorid not uncommonly found in some alkali regions is undoubtedly the product of the above reaction.

As the saline solutions in the soil are mostly quite dilute, and calcic carbonate is always present, it follows that whenever under the influences which favor the oxidation of organic matter in the soil, and the activity of the plant roots, carbonic gas is formed somewhat copiously, alkali sulfates and chlorids present may be partially or wholly transformed into carbonates within the soil. As a matter of fact, it is found that this transformation occurs most readily in the moister portions of the soil and subsoil, and invariably so when an alkali soil is “swamped” by excessive irrigation or rise of bottom water; while the reaction is again reversed whenever free access of air reduces the carbonic dioxid below a certain point. It thus becomes intelligible why in the diagrams showing the distribution of the salts (this chapter pp. 431 and 432), we always find the sodic carbonate relatively decreasing as the surface is approached.

Thus, also, is explained the fact that sodium carbonate is formed more abundantly toward the center of the root system of alkali plants, such as the greasewood, beneath which the soil is always more abundantly charged with “black alkali” than is the surrounding earth.

Good aeration of the soil mass, then, is essential in maintaining the neutralization of the “black alkali” soils brought about by the use of gypsum (land plaster).

Inverse Ratios of Alkali Carbonates and Sulfates.—According to the above considerations, it is not surprising that we should often find an apparent inverse ratio between the alkali sulfates and carbonates in soils so closely adjacent that their salts must be presumed to be similar in composition. A striking example is shown in fig. 70, in which this inverse ratio becomes apparent four times in succession in one and the same soil profile. While this inference is plain on the face of the diagram, it is not quite easy to explain in detail how this alternation came about from the condition observed two months previously. Most probably it was caused by corresponding alternations of weather, in which short, warm spring showers alternated with similarly brief periods of drying north winds; the latter causing a reversal of the formation of sodic carbonate that had been induced by the former.

Exceptional Conditions.—While the phenomena of alkali lands as outlined above probably represent the vastly predominant conditions on level lands, yet there are exceptions due to surface conformation, and the local existence of sources of alkali salts outside of the soil itself. Such is the case where salts ooze out of strata cropping out on hillsides, as at some points in the San Joaquin Valley in California, and in parts of New Mexico, Colorado and Wyoming; also where, as in the Hungarian plain, saline clays underlie within reach of surface evaporation.

Again, it not infrequently happens that in sloping valleys or basins, where the central (lowest) portion receives the salts leached out of the soils of the adjacent slopes, we find belts of greater or less width in which the alkali impregnation may reach to the depth of ten or twelve feet, usually within more or less definite layers of calcareous hardpan, likewise the outcome of the leaching of the valley slopes. Such areas, however, are usually quite limited, and are at present scarcely reclaimable without excessive expenditure; the more as they are often underlaid by saline bottom water. In these cases the predominant saline ingredient is usually common salt, as might be expected and as is exemplified in the Great Salt Lake of Utah, in the Antelope and Perris Valleys, and in Salton basin in California; in the Yellowstone valley near Billings, Mont. in the Aralo-Caspian desert, and at many other points.

Farmer’s Bull. No. 88, U. S. Dept. Agr., 1899.

Conclusions.—Summing up the conclusions from the foregoing facts and considerations, we find that—

(1) The amount of soluble salts in alkali lands is usually limited; they are not ordinarily supplied in indefinite quantities from the bottom-water below. These salts have mostly been formed by weathering in the soil-layer itself.

(2) The salts move up and down within the upper four or five feet of the soil and subsoil, following the movement of the moisture; descending in the rainy season to the limit of the annual moistening as a maximum, and then reascending or not, according as surface evaporation may demand. At the end of the dry season, in untilled irrigated land, practically the entire mass of salts may be within six or eight inches of the surface.

(3) The direct injury to vegetation is caused largely within a few inches of the surface, by the corrosion of the bark, usually near the root crown. This corrosion is strongest when carbonate of soda (salsoda) forms a large proportion of the salts; the soda then also dissolves the vegetable mold and causes blackish spots in the soil, popularly known as black alkali.

For a general statement and discussion of the physiological effects of saline solutions on plants, see chapter 26.

(4) The injury caused by carbonate of soda is aggravated by its action in puddling the soil so as to cause it to lose its crumbly or flaky condition, rendering it almost or quite untillable and impervious. It also tends to form in the depths of the soil-layer a tough, impervious hardpan, which yields neither to plow, pick, nor crowbar. Its presence is easily ascertained by means of a pointed steel sounding-rod.

(5) While alkali lands share with other soils of the arid region the advantage of unusually high percentages of plant-food in the insoluble form, they also contain, alongside of the noxious salts, considerable amounts of water-soluble plant-food. When, therefore, the action of the noxious salts is done away with, they should be profusely and lastingly productive; particularly as they are always naturally somewhat moist in consequence of the attraction of moisture by the salts, and are therefore less liable to injury from drought than the same soils when free from alkali.