XXII. 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.[162] 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.
[162] 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[163] 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.
[163] 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,”[164] 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.
[164] 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.
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,[165] 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.
[165] 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.
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.
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.[166] Subsequently, a more elaborate investigation of the subject was made by Dr. J. W. Leather, Agricultural Chemist to the Government of India.[167] 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).
[166] An abstract of the report of this commission is given in the Report of the California Experiment Station for 1890.
[167] 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[168] 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;[169] 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.
[168] 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.
[169] 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,[170] 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.
[170] 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.[171] 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.
[171] 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.[172] in the Aralo-Caspian desert, and at many other points.
[172] 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[173] 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.
[173] 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.
XXIII. UTILIZATION AND RECLAMATION OF ALKALI LANDS
Alkali-Resistant Crops.—The most obvious mode of utilizing alkali lands is to occupy them with crops not affected by the noxious salts. Unfortunately but few such crops of general utility have as yet been found for the stronger class of alkali lands. The question is always one of degree, which frequently cannot be decided without an actual determination of the amount and kind of salts to be dealt with, to which the crops can then be adapted in accordance with the greater or less sensitiveness of the several plants, as indicated in the table of tolerances given farther on. But aside from this, there are certain general measures and precautions which in any case will serve to mitigate the effect of the alkali salts. Foremost among these, and applicable everywhere, is the prevention of evaporation to the utmost extent possible.
Counteracting Evaporation.—Since evaporation of the soil-moisture at the surface is what brings the alkali to the level where the main injury to plants occurs, it is obvious that evaporation should be prevented as much as possible. This is the more important, as the saving of soil-moisture, and therefore of irrigation water, is attainable by the same means.
Three methods for this purpose are usually practiced, viz., shading, mulching, and the maintenance of loose tilth in the surface soil to such depth as may be required by the climatic conditions.
As to mulching, it is already well recognized in the alkali regions of California as an effective remedy in light cases. Fruit trees are frequently thus protected, particularly while young, after which their shade alone may (as in the case of low-trained orange trees) suffice to prevent injury. The same often happens in the case of low-trained vines, small-fruit, and vegetables. Sanding of the surface to the depth of several inches was among the first attempts in this direction; but the necessity of cultivation, involving the renewal of the sand each season, renders this a costly method. Straw, leaves, and manure have been more successfully used; but even these, unless employed for the purpose of fertilization, involve more expense and trouble than the simple maintenance of very loose tilth of the surface soil throughout the dry season; a remedy which, of course, is equally applicable to hoed field crops, and is in the case of some of these—e. g., cotton—a necessary condition of cultural success everywhere. The wide prevalence of “light” soils in the arid regions, from causes inherent in the climate itself, renders this condition relatively easy of fulfilment.
Turning-under of Surface Alkali.—Aside, however, from the mere prevention of surface evaporation, another favorable condition is realized by this procedure, namely the commingling of the heavily salt-charged surface-layers with the relatively non-alkaline subsoil. Since in the arid regions the roots of all plants retire farther from the surface because of the deadly drought and heat of summer, it is usually possible to cultivate deeper than could safely be done with growing crops in humid climates. Yet even there, the maxim of “deep preparation and shallow cultivation” is put into practice with advantage, only changing the measurements of depth to correspond with the altered climatic conditions. Thus while in the humid States, three to four inches is the accepted standard of depth for summer cultivation to preserve moisture without injury to the roots, that depth must in the arid region frequently be doubled in order to be effective; and will even then scarcely touch a living root in orchards and vineyards, particularly in unmanured and unirrigated land.
A glance at fig. 63, (chap. 22, p. 431), will show the great advantage of extra-deep preparation in commingling the alkali salts accumulated near the surface with the lower soil-layers, diffusing the salts, say through twelve instead of six inches of soil mass. This will in very many cases suffice to render the growth of ordinary crops possible if, by subsequent frequent and thorough cultivation, surface evaporation, and with it the re-ascent of the salts to the surface, is prevented.
A striking example of the efficiency of this mode of procedure was observed at the Tulare substation, California, where a portion of a very bad alkali spot was trenched to the depth of two feet, throwing the surface soil to the bottom. The spot thus treated produced excellent wheat crops for two years—the time it took the alkali salts to reascend to the surface.
It should therefore be kept in mind that whatever else is done toward reclamation, deep preparation and thorough cultivation must be regarded as prime factors for the maintenance of production on alkali lands.
The Efficacy of Shading, already referred to, is strikingly illustrated in the case of some field crops which, when once established, will thrive on fairly strong alkali soil, provided that a good thick “stand” has once been obtained. This is notably true of the great forage crop of the arid region, alfalfa or lucern. Its seed is extremely sensitive to “black” alkali, and will decay in the ground unless protected against it by the use of gypsum in sowing. But when once a full stand has been obtained, the field may endure for many years without a sign of injury. Here two effects combine, viz., the shading, and the evaporation through the deep roots and abundant foliage, which alone prevents, in a large measure, the ascent of the moisture and salts to the surface. The case is then precisely parallel to that of the natural soil (see p. 432, chapter 22), except that, as irrigation is practiced in order to stimulate production, the sheet of alkali hardpan will be dissolved and its salts spread through the soil more evenly. The result is that so soon as the alfalfa is taken off the ground and the cultivation of other crops is attempted, an altogether unexpectedly large amount of alkali comes to the surface and greatly impedes, if it does not altogether prevent, the immediate planting of other crops. Shallow-rooted annual crops that give but little shade, like the cereals, while measurably impeding the rise of the salts during their growth (see fig. 70, page 452) frequently allow of enough rise after harvest to prevent reseeding the following season.
“Neutralising” Black Alkali.—Since so little carbonate of soda as one-tenth of one per cent may suffice to render some soils uncultivable, it frequently happens that its mere transformation into the sulfate is sufficient to remove all stress from alkali. Gypsum (land plaster) is the cheap and effective agent to bring about this transformation, provided water be also present. The amount required per acre will, of course, vary with the amount of salts in the soil, all the way from a few hundred pounds to several tons in the case of strong alkali spots; but it is not usually necessary to add the entire quantity at once, provided that sufficient be used to neutralize the sodic carbonate near the surface, and enough time be allowed for the action to take place. In very wet soil, and when much gypsum is used, this may occur within a few days; in merely damp soils in the course of months; but usually the effect increases for years, as the salts rise from below.
The effect of gypsum on black-alkali land is often very striking, even to the eye. The blackish puddles and spots disappear, because the gypsum renders the dissolved humus insoluble and thus restores it to the soil. The latter soon loses its hard, puddled condition and crumbles and bulges into a loose mass, into which water now soaks freely, bringing up the previously depressed spots to the general level of the land. On the surface thus changed, seeds now germinate and grow without hindrance; and as the injury from alkali occurs at or near the surface, it is usually best to simply harrow in the plaster, leaving the water to carry it down in solution. Soluble phosphates present are decomposed so as to retain finely divided, but less soluble earth phosphates in the soil.
It must not be forgotten that this beneficial change may go backward if the land thus treated is permitted to be swamped by irrigation water or otherwise. Under the same conditions naturally white alkali may turn black (see above, chapter 22, p. 451). Of course, gypsum is of no benefit whatever on soils containing no “black” alkali, but only (“white”) Glauber’s and common salt.
Removing the Salts from the Soil.—In case the amount of salts in the soil should be so great that even the change worked by gypsum is insufficient to render it available for useful crops, the only remedy left is to remove the salts, partially or wholly, at least from the surface of the land. Three chief methods are available for this purpose. One is to remove the salts, with more or less earth, from the surface at the end of the dry season, either by sweeping or by means of a horse scraper set so as to carry off a certain depth of soil. Thus sometimes in a single season one-third or one-half of the total salts may be got rid of, the loss of a few inches of surface soil being of little moment in the deep soils of the arid region. Another method affording partial relief is to flood the land for a sufficient length of time to carry the alkali three or more feet below the surface, then carefully preventing its re-ascent by suppressing evaporation (see this chapter, p. 455) as much as possible. The best of all, the final and universally efficient remedy, is to leach the alkali salt out of the soil into the country drainage; supplementing by irrigation water what is left undone by the deficient rainfall.
It is not practicable, as many suppose, to wash the salts off the surface by a rush of water, as they instantly soak into the ground at the first touch. Nor is there any certain relief from allowing the water to stand on the land and then drawing it off; in this case also the salts soak down ahead of the water, and the water standing on the surface remains almost unchanged. In very pervious soils and in the case of white alkali, the washing-out can often be accomplished without special provision for underdrainage, by leaving the water on the land sufficiently long. But the laying of regular underdrains greatly accelerates the work, and renders success certain.
Leaching-Down.—In advance of underdrainage, it is quite generally feasible, where the land has been leveled and diked for irrigation by surface flooding, to leach the salts out of the first three or four feet by continued flooding, thus taking them out of reach of the crop roots, or at all events giving the seed an opportunity to escape injury from alkali. This plan is especially effective in the case of alfalfa, the young seedlings of which are very sensitive, while the grown plant is rather resistant. In order to obtain this relief so as to know what is being accomplished, the farmer should ascertain beforehand how fast water will soak down in his ground;[174] for in heavy clay soils, and especially in those containing black alkali, the soakage is sometimes so slow that the upward diffusion of the salts keeps pace with the downward soakage; in which case nothing is accomplished by flooding, and underdrainage is the only remedy. But in most soils of the arid region flooding from three days to a week will remove the alkali beyond reach of the roots of ordinary crops. If subsequently irrigation is done by means of deep furrows, the alkali salts may be either kept at a low level continuously, or if the land be at all pervious, the alkali may ultimately be permanently leached out into the subdrainage by farther flooding. When the alkali has not accumulated near the surface to any great extent, irrigation by deep furrows may, alone, afford all the relief needed.
[174] See p. 242, Chap. 13.
In the case illustrated by figures 71 and 72, irrigation by shallow furrows with water too strongly charged with salts had so far added to the natural alkali-content of the land that the lemon trees were being defoliated. Upon the advice of the California Station the deep-furrow system was adopted, and within two years the results were as shown in figure 72, the salts having been carried down and diluted so as to become harmless.
Underdrainage the Final and Universal Remedy for Alkali.—When we underdrain an alkali soil, we adopt the very means by which the existence of alkali lands in the humid regions is wholly prevented; the leaching-out of the soluble salts formed in soil-weathering as fast as they are formed. The long and abundant experience had with underdrainage in reclaiming saline sea-coast lands, applies directly and cogently to alkali lands. It is the universal remedy for all the evils of alkali, and its only drawback is the first expense, and the necessity for obtaining an outlet for the drain waters, which cannot always be had on the owner’s land. Hence it requires co-operation or legislation to render the great improvement of underdrainage feasible. Such legislation is well established in the old world, and has been enacted in several states even of the humid region. Where irrigation is practiced as a matter of necessity, underdrainage is a correlative necessity, both to avoid the evils of over-irrigation and to relieve the land of noxious alkali salts.
The drainage law now existing in California does not go farther than to authorize the formation of drainage districts, within which the necessary taxes may be levied; and there is some difficulty in securing popular action. But bitter experience will doubtless in time compel unanimity, such as now exists, e. g., in Illinois, where drainage is not nearly so urgently needed as it is in the irrigation states.
Possible Injury to Land by Excessive Leaching.—It should not be forgotten, however, that excessive leaching of underdrained land by flooding is liable to injure the soil in two ways: first, by the removal of valuable soluble plant-food; and further, by rendering the land less retentive of moisture, such retention being favored by the presence of small amounts of alkali salts, not sufficient to injure crops. After the salts have been carried down to a sufficient depth to prevent injury to annual crops, and with proper subsequent attention to the prevention of surface evaporation, the flooding will not need to be repeated for several years. Thus in many soils excellent crops may be grown even in strong alkali land, pending the establishment of permanent drainage systems.
The importance of thoroughly washing the alkali deeply into the soil before the seed is planted, and keeping it there by proper means until the foliage of the plant shades the soil sufficiently to prevent the rise of moisture and alkali, is well illustrated in fields in the region of Bakersfield, Cal., where alfalfa is now growing in soils once heavily charged with alkali.[175] From one of these fields samples of soil were taken where the alkali was supposed to be strongest beneath the alfalfa, and also from an adjoining untreated alkali spot, which was said to represent conditions before alfalfa was planted. The results are given in pounds per acre in four feet depth.
===========================+========+==========+=========+======== |Sulfate.|Carbonate.| Common | Total | | | Salt. | Alkali. ---------------------------+--------+----------+---------+-------- Alkali spot before alfalfa | | | | was planted | 60,120 | 720 | 175,840 | 236,680 | | | | Alfalfa field; alkali | | | | washed down | 14,400 | | 1,040 | 18,640 ---------------------------+--------+----------+---------+--------
Here the surface foot of the natural soil contained nearly 140,000 pounds of common salt, a prohibitory amount. Similar experience has been had near Yuma, Arizona.
[175] Bull. 133, Cal. Expt. Sta., by R. H. Loughridge.
Difficulty in Draining “Black” Alkali Lands.—An important exception to the efficacy of draining, however, occurs in the case of black alkali in most lands. In this case either the impervious hardpan or (in the case of actual alkali spots) the impenetrability of the surface soil itself will render even underdrains ineffective unless the salsoda and its effects on the soil are first destroyed by the use of gypsum, as above detailed. This is not only necessary in order to render drainage and leaching possible, but is also advisable in order to prevent the leaching-out of the valuable humus and soluble phosphates, which are rendered insoluble (but not unavailable to plants) by the action of the gypsum. Wherever black alkali is found in lands not very sandy, the application of gypsum should precede any other efforts toward reclamation. Trees and vines already planted may be temporarily protected from the worst effects of the black alkali by surrounding the trunks with gypsum or with earth abundantly mixed with it. Seeds may be similarly protected in sowing, and young plants in planting.
Swamping of Alkali Lands.—It should, however, be remembered that the swamping of alkali lands, whether of the white or black kind, is fatal not only to their present productiveness, but also, on account of the strong chemical action thus induced, greatly jeopardizes their future usefulness. Many costly investments in orchards and vineyards have thus been rendered unproductive, or have even become a total loss.
Reduction of Alkali by Cropping.—Another method for diminishing the amount of alkali in the soil is the cropping with plants that take up considerable amounts of salts. In taking them into cultivation, it is advisable to remove entirely from the land the salt growth that may naturally cover it, notably the greasewoods (Sarcobatus, Allenrolfea), with their heavy percentage of alkaline ash (12 to 20 per cent). Crop plants adapted to the same object are mentioned farther on. Such crops should also, of course, be wholly removed from the land.
Total Amounts of Salts Compatible with Ordinary Crops; Tolerance of Culture Plants.—Since the amount of alkali that reaches the surface layer is largely dependent upon the varying conditions of rainfall or irrigation, and surface evaporation, it is difficult to foresee to what extent that accumulation may go, unless we know the total amount of salts present that may be called into action. This, as already explained, can ordinarily be ascertained by the examination of one sample representing the average of a soil column of four feet. By calculating the figures so obtained to an acre of ground, we can at least approximate the limits within or beyond which crops will succeed or perish. Applying this procedure to the cases represented in the diagrams (pp. 434, 452, chapter 22) and estimating the weight of the soil per acre-foot at 4,000,000 pounds, we find in the land on which barley refused to grow the figures 32,470 and 43,660 pounds of total salts per acre, respectively corresponding to 0.203 per cent for the first figure (the second, representing only the two surface feet, is not strictly comparable). For the land on which barley gave a full crop, we find for the May sample 25,550 pounds, equivalent to 0.159 per cent for the whole soil column of four feet. It thus appears that for barley the limits of tolerance lie between the above two figures. It should be noted that in this case a full crop of barley was grown even when the alkali consisted of fully one-half of the noxious carbonate of soda; proving that it is not necessary in every case to neutralize the entire amount of that salt by means of gypsum, which in the present case would have required about 9½ tons of gypsum per acre—a prohibitory expenditure.
Relative Injuriousness of the Several Salts.—Of the three sodium salts that usually constitute the bulk of “alkali,” only the carbonate of soda is susceptible of being materially changed by any agent that can practically be applied to land. So far as we know, the salt of sodium least injurious to ordinary vegetation is the sulfate, commonly called Glauber’s salt, which ordinarily forms the chief ingredient of “white” alkali. Thus barley is capable of resisting about five times more of the sulfate than of the carbonate, and quite twice as much as of common salt. Since the maximum percentage that can be resisted by plants varies materially with the kind of soil, it is difficult to give exact figures save with respect to particular cases. For the sandy loam of the Tulare substation, California, for instance, the maximum for cereals may be approximately stated to be one-tenth of 1 per cent for salsoda; a fourth of 1 per cent for common salt; and from forty-five to fifty one-hundredths of one per cent of Glauber’s salt. For clay soils the tolerance is in general markedly less, especially as regards the salsoda; since in their case the injurious effect on the tilling qualities of the soil, already referred to, is superadded to the corrosive action of that salt upon the plant.
Effect of Differences in Composition of Alkali Salts on Beets.—The marked differences which may occur as the result of even slight variations in the proportions of the several salts is well illustrated in the subjoined diagram of observations made by Dr. G. W. Shaw, of the Cal. Expt. station, upon beet fields in the neighborhood of Oxnard, Cal. The lands lie not far from the seashore, and saline water underruns them for considerable distance inland. The soil and subsoil are quite sandy, so that it takes irrigation water only about seven hours to penetrate from the surface to bottom water at seven feet depth. The land on which these observations were made are apparently level to the eye, though probably the alkali belts on which the sugar beets were “poor” are slightly depressed swales.
It will be noted that here the beets were “good” where the sulfate (Glauber’s salt) ranged up to .8%, with .10 to .20 of common salt; but that so soon as the latter rose above .20, the beets were poor despite the low percentage of Glauber’s salt; then became “good” again so soon as the common salt fell below .20%, although the Glauber’s salt increased.
TOLERANCE OF VARIOUS CROP PLANTS.
The following table, compiled by Dr. R. H. Loughridge mainly from his own observations,[176] gives the details of the tolerance for various culture plants as ascertained at the several experiment substations in California, as well as at other points in that State and in Arizona where critical cases could be found. It is thought preferable to investigate analytically such cases in the field, rather than to attempt to obtain results from small-scale experiments artificially arranged, in which sources of error arising from evaporation and other causes are most difficult to avoid.
[176] Bulletins Nos. 128, 133 and 140, Calif. Expt. Station.
The table is so arranged as to show the maximum tolerance thus far observed for each of the three single ingredients, as well as the maximum of total salts found compatible with good growth. In view of the extremely variable proportions between the three chief ingredients found in nature, this seems to be the only manner in which the observations made can be intelligibly presented, until perhaps a great number of such data shall enable us to evolve mathematical formulæ expressing the tolerance for the possible mixtures for each plant. For it is certain that the tolerance-figures will be quite different in presence of other salts, from those that would be obtained for each salt separately; or for the calculated mean of such separate determinations, proportionally pro-rated. It must also be remembered that in all alkali soils, lime carbonate is abundantly present, as is, nearly always, a greater or less amount of the sulfate (gypsum). As already stated, according to the investigations of Cameron not only these compounds, but also calcium chlorid, exert a protective influence against the injury to plant growth from compounds of sodium and potassium. The figures here given can therefore be regarded only as approximations, subject to correction by farther observation. They are arranged from the highest tolerances downward, for each of the three ingredients, as well as for the totals. The latter are not, of course, the sums of the figures given in the preceding columns, but independent data.
HIGHEST AMOUNT OF ALKALI IN WHICH FRUIT TREES WERE FOUND UNAFFECTED.[177]
Arranged from highest to lowest. Pounds per acre in four feet depth.
=================+===============+================+================= Sulfates | Carbonate | Chlorid | Total Alkali. (Glauber’s Salt).| (Salsoda). | (Common Salt).| -----------------+---------------+----------------+----------------- Grapes 40,800| Grapes 7,550| Grapes 9,640| Grapes 45,700 Olives 30,640| Oranges 3,840| Olives 6,640| Olives 40,160 Figs 24,480| Olives 2,880| Oranges 3,360| Almonds 25,560 Almonds 22,720| Pears 1,760| Almonds 2,400| Figs 26,400 Oranges 18,600| Almonds 1,440| Mulberry 2,240| Oranges 21,840 Pears 17,800| Prunes 1,360| Pears 1,360| Pears 20,920 Apples 14,240| Figs 1,120| Apples 1,240| Apples 16,120 Peaches 9,600| Peaches 680| Prunes 1,200| Prunes 11,800 Prunes 9,240| Apples 640| Peaches 1,000| Peaches 11,280 Apricots 8,640| Apricots 480| Apricots 960| Apricots 10,080 Lemons 4,480| Lemons 480| Lemons 800| Lemons 5,760 Mulberry 3,360| Mulberry 160| Figs 800| Mulberry 5,760 -----------------+---------------+----------------+-----------------
[177] The several columns of figures are independent of each other; the “total” alkali is not the summation for the three salts in the same line.
OTHER TREES. ---------------------+-------------------+-------------------- Kölreuteria 51,040| Kölreuteria 9,920| Or. Sycamore 20,320 Eucal. am. 34,720| Or. Sycamore 3,200| Kölreuteria 12,640 Or. Sycamore 19,240| Date Palm. 2,800| Eucal. am. 2,960 Wash. Palm 13,040| Eucal. am. 2,720| Camph. Tree 1,420 Date Palm 5,500| Wash. Palm 1,200| Wash. Palm 1,040 Camph. Tree 5,280| Camph. Tree 320| ---------------------+-------------------+-------------------- Kölreuteria 73,600 Or. Sycamore. 42,760 Eucal. am. 40,400 Wash. Palm 15,200 Date Palm 8,328 Camph. Tree 7,020 ---------------------
SMALL CULTURES. ---------------------+-------------------+--------------------- Saltbush 125,640| Saltbush 18,560| Modiola 40,860 Alfalfa, old 102,480| Barley 12,170| Saltbush 12,520 Alfalfa, young 11,120| Bur Clover 11,300| Sorghum 9,680 Hairy Vetch 63,720| Sorghum 9,840| Celery 9,600 Sorghum 61,840| Radish 8,720| Onions 5,810 Sugar Beet 52,640| Modiola 4,760| Potatoes 5,810 Sunflower 52,640| Sugar Beet 4,000| Sunflower 5,440 Radish 51,880| Gluten Wheat 3,000| Sugar Beet[178] 10,240 Artichoke 38,720| Artichoke 2,760| Barley 5,100 Carrot 24,880| Lupin 2,720| Hairy Vetch 3,160 Gluten Wheat 20,960| Hairy Vetch 2,480| Lupin 3,040 Wheat 15,120| Alfalfa 2,360| Carrot 2,360 Barley 12,020| Grasses 2,300| Radish 2,240 Goat’s Rue 10,880| Kaffir Corn 1,800| Rye 1,720 Rye 9,800| Sweet Corn 1,800| Artichoke 1,480 Cañaigre 9,160| Sunflower 1,760| Gluten Wheat 1,480 Ray Grass 6,920| Wheat 1,480| Wheat 1,160 Modiola 6,800| Carrot 1,240| Grasses 1,000 Bur Clover 5,700| Rye 960| White Melilot 440 Lupin 5,440| Goat’s Rue 760| Goat’s Rue 160 White Melilot 4,920| White Melilot 480| Cañaigre 80 Celery 4,080| Cañaigre 120| Saltgrass 44,000| Saltgrass 136,270| Saltgrass 70,360 ----------------------+-------------------+--------------------- Saltbush 156,720 Alfalfa, old 110,320 Alfalfa, young 13,120 Sorghum 81,360 Hairy Vetch 69,360 Radish 62,840 Sunflower 59,840 Sugar Beet 59,840 Modiola 52,420 Artichoke 42,960 Carrot 28,480 Barley 25,520 Gluten Wheat 24,320 Wheat 17,280 Bur Clover 17,000 Celery 13,680 Rye 12,480 Goat’s Rue 11,800 Lupin 11,200 Cañaigre 9,360 Onions 38,480 Potatoes 38,480 Saltgrass 381,110 ----------------------
[178] Figures taken from Bulletin 169, Calif. Expt. Station, June, 1905.
Comments on the Above Table.—Considering in this table, first, the plants suitable for the stronger class of alkali lands, it may be said generally that the search for widely acceptable kinds has not been very successful. It is true that cattle will nibble green salt grass (Distichlis spicata), but will soon leave it for any dry feed that may be within reach. The enormous amount of salts which it will tolerate in the soil on which it grows, and the doubtless correspondingly large amount of those salts which it will absorb, judging from its taste, sufficiently explain the reluctance of cattle to feed on it to any considerable extent.
The same is true of all the fleshy plants that grow on the stronger alkali lands, and are known under the general designation of “alkali weeds.” When stock unaccustomed to it are forced by hunger to feed on such vegetation to any considerable extent, disordered digestion is apt to result; which in such ranges, however, is often counteracted by feeding on aromatic or astringent antidotes, such as the gray sagebrush and the more or less resinous herbage of plants of the sunflower family.
In the Great Basin region, lying between the Sierra Nevada and the front range of the Rocky Mountains, there are, aside from the grasses, numerous herbaceous and shrubby plants that afford valuable pasturage for stock,[179] and some of these grow on moderately strong alkali land; the same is true in California. It is quite possible that some of these will be found to lend themselves to ready propagation for culture purposes as well as they do for restocking the ranges. But thus far none have found wider acceptance, probably because their stiff branches and upright habit render them inconvenient to handle. It will require more extended experience and experiment before any of these will be definitely adopted for propagation by farmers and stockmen.
[179] See Bulletin No. 16 of the Wyoming Experiment Station; also Bulletin Nos, 2 and 12 of the Division of Agrostology, and Farmers’ Bulletin No. 108, U. S. Department of Agriculture.
Saltbushes, and Herbaceous Crops.
Australian Saltbushes.—Experience in California indicates that in the more southerly portion of the arid region, unpalatable native plants may be largely replaced, even on the ranges, by one or more species of the Australian saltbushes (Atriplex spp.), long ago recommended by Baron von Mueller of Melbourne; of which one (A. semibaccata) has proved eminently adapted to the climate and soil of California and is readily eaten by all kinds of stock. The facility with which it is propagated, its quick development, the large amount of feed yielded on a given area, even on the strongest alkali land ordinarily found, and its thin, flexible stems, permitting it to be handled very much like alfalfa, seem to commend it especially to the farmers’ consideration wherever better forage plants cannot be grown and the climate will permit of its use. It does not, however, resist the severe cold of the interior plateau country, and is wholly out of place in the Pacific Coast region where summer fogs prevail. Most of the other Australian species have an upright, shrubby habit, which adapts them better to browsing than to pasture proper. The same is true of the Argentine species (A. Cachiyuyum), which in its native pampas is highly esteemed for that purpose, and succeeds well in California. Of other Australian saltbushes, A. halimoides, vesicaria and leptocarpa are the most promising; the latter is somewhat similar in habit to the semibaccata, but is not as vigorous a grower. Since some of the saltbushes take up nearly one fifth of their dry weight of ash ingredients,[180] largely common salt, the complete removal from the land of a five-ton crop of saltbush hay will take away nearly a ton of the alkali salts per acre. This will in the course of some years be quite sufficient to reduce materially the saline contents of the land, and will frequently render possible the culture of ordinary crops.
[180] Analyses made at the California station show 19.37 percent of ash in the air-dry matter of Australian saltbush. (See California Station Bulletin No. 105; E. S. R., vol. 6, p. 718). Analyses of Russian thistle have been reported showing over 20 per cent of ash in dry matter. (See Minnesota Sta. Bulletin No. 34; Iowa Sta. Bull. No. 26; E. S. R., vol. 6, pp. 552-553).
Modiola.—Alongside of the saltbushes, the Chilean plant Modiola procumbens, now generally known as modiola simply, deserves attention, as it makes acceptable pasture where alfalfa fails to make a stand on account of alkali. It is a trailing plant with medium-sized, roundish foliage, and roots freely at the joints where they touch the ground. Unlike the saltbushes it is therefore a formidable weed where it is not wanted; but as according to California experience it resists as much as 52,000 pounds of salts per acre, even when 41,000 of these is common salt, it is likely to be useful in many cases, particularly as an admixture to a saltbush diet for stock, as it does not absorb as much salt as the latter. It seems best adapted to pasturage.
As the table shows that, once grown to the age of a few years, alfalfa will resist a percentage of alkali next to the saltbush, it will generally be worth while, in lands otherwise adapted to alfalfa, to prepare the land by leaching-down (see above) so as to secure a stand of the more valuable crop.
Native Grasses.[181]—Of all known plants that stock will eat somewhat freely, the tussock grass (Sporobolus airoides, of which a figure is given farther on), a native of the southern arid region, endures the largest amounts of alkali; having been found growing well on land containing the enormous amount of nearly half a million pounds of salts per acre, although it will thrive with only 49,000 pounds in the soil. What it will do under cultivation has never been fairly tested; but its bare tussocks, killed by the excessive browsing of stock, testify to its acceptableness as forage. It does not seem to absorb excessive amounts of salts.
[181] It should be understood that the plants so referred to are exclusively the true grasses, recognized as such by every child, and not forage plants generally; which are sometimes so designated; not only by farmers, but by some authors who fail to appreciate the practical importance of the distinction, which makes it necessary that farmers should be taught to understand it.
Aside from the alkali grass proper (Distichlis), mentioned above, the so-called rye grass of the Northwest (Elymus condensatus) is probably, next to the tussock grass, the most resistant species among the wild grasses. Its southern form, with several others not positively identified, occupies largely the milder alkali lands of southern California. This grass, though rather coarse, is regularly cut for hay in the low grounds of Oregon and Washington.
Doubtless some of the indigenous grasses of the interior plateau region and of the great plains east of the Rocky Mountains, such as the buffalo and grama grasses, as well as several of the wheat grasses (Agropyron) and bunch grasses (Festuca, Poa, Stipa, etc.) will prove resistant to larger proportions of alkali than the meadow and pasture grasses of the regions of summer rains.
Cultivated Grasses.—The superficial rooting and fine fibrous roots of the true annual grasses render them, as a whole, rather sensitive to alkali; yet the cereals—barley, wheat, rye and oats—resist, as the table shows, the average alkali salts to the extent of from 17,000 total salts, with not exceeding 1500 pounds of carbonate, in the case of the more delicate varieties of wheat, to over 25,000 pounds per acre in the case of barley, which with the gluten wheats and rye seems to have the highest tolerance-figure. The special adaptation of gluten wheats to arid conditions is thus emphasized. The roots of these cereals are comparatively stout, with thick epidermis.
Among the cultivated forage grasses proper, the Australian variety of the English ray (generally miscalled rye) grass seems most resistant. The eastern fescues, Kentucky blue grass, and others at home in the humid region are easily injured, as those who try to maintain lawns on alkali-tainted lands, or by irrigation with alkali waters, know to their sorrow. To these grasses common salt and bittern (magnesium chlorid) seem to be particularly injurious, and they tolerate but little “black alkali.”
On the rather close-textured soil at Chino, California, the loliums, including the darnel (“California cheat”), and the Australian and Italian ray (“rye”) grasses, succeed fairly on land containing as much as 6,000 pounds of (white) salts. Most other cultivated grasses failed conspicuously alongside of these. It must be remembered that in more loose-textured, sandy lands than those in which these tests were made, the above figures for tolerance would probably be increased by 30 percent or more.
Maize is rather sensitive to alkali, and suffers even on slightly alkaline land, owing doubtless to the large development of fine white rootlets near the surface, so familiar to corn-growers. The Sorghums, and especially Egyptian corn (durra) are much less sensitive, as the table shows, and are among the first crops to be tried on alkali lands. The related millets share this resistance more or less, and we often see on cultivated lands in the alkali region fine stands of barnyard grass (Panicum crusgalli) of which the variety (?) P. muticum is said by observers of the U. S. Dept. of Agriculture to be specially resistant, and acceptable to stock. One of the most successful grasses on the light alkali lands near Chino, where most of the commonly cultivated grasses fail, was a near relative of the barnyard grass, the Eleusine coracana, which produces heavy crops of a millet-like grain much relished by poultry, and also by stock. This grass, largely grown in Egypt, has succeeded well all over the ground whose alkali content ranges up to 12,000 pounds per acre, but failed where the salts reached 38,840 pounds in the surface foot. Next to this, in point of success, were the pearl millet (Pennisetum typhoideum) and teosinte, Hungarian brome grass, and Japanese millet, on land containing about 9,000 pounds of (chiefly “white”) salts per acre.
Other Herbaceous Crops. Legumes.—Both the natural growth of alkali lands and experimental tests seem to show that this entire family (peas, beans, clovers, etc.) are among the more sensitive and least available wherever black alkali exists; while fairly tolerant of the white (neutral) salts. Apparently a very little salsoda suffices to destroy the tubercle-forming organisms that are so important a medium of nitrogen-nutrition in these plants. Excepting the melilots, alfalfa with its hard, stout and long taproot, seems to resist best of all these plants.
As a general thing, taprooted plants, when once established, resist best, for the obvious reason that the main mass of their feeding roots reaches below the danger level. Another favoring condition, already alluded to, is heavy foliage and consequent shading of the ground; alfalfa happens to combine both of these advantages. There has been some difficulty in obtaining a full stand of alfalfa in the portion of the Chino substation tract containing from 4000 to 6000 pounds of (largely black) alkali salts per acre; but once obtained, it has done very well.
The only other plant of this family that succeeds well on this land, and even (at Tulare) on soil considerably stronger (probably between 20,000 and 30,000 pounds) are the two melilots, M. indica, and alba; the latter (the Bokhara clover) is a forage plant of no mean value in moist climates, but somewhat restricted in its use in the arid region because of the very high aroma it develops, especially in alkali lands; so that stock will eat only limited amounts, best when intermixed with other forage, such as the saltbushes. The yellow melilot is highly recommended by the Arizona Experiment Station as a green-manure plant for winter growth; but farther north it is a summer-growing plant only, and is refused by stock. As already stated, very few plants belonging to this family are naturally found on alkali lands, and attempts to grow them, even where only Glauber’s salt is present, have been but very moderately successful.
For most of the legumes the limit of full success seems to lie between 3000 and 4000 pounds to the acre. A marked exception, however, occurs in the case of the hairy vetch, as shown in the table, where it is credited, on the basis of repeated experiments, with a tolerance of nearly 70,000 pounds. This amount was attained, however, in rather sandy soils. Probably some of the Algerian vetches will likewise prove more resistant than those which are natives of humid climates.
Mustard Family.—As in the case of the legumes, wild plants of the mustard family are rare on alkali lands; and correspondingly, the cultivated mustard, kale, rape, etc., fail even on land quite weak in alkali. Their limit of tolerance seems to lie near 4,000 to 5,000 pounds per acre even of white salts. Hence turnips and radishes do not flourish on alkali lands.
Sunflower Family.—Several of the hardiest of the native “alkali weeds” belong to the sunflower family, and the common wild sunflowers (Helianthus californicus and H. annuus) are common on lands pretty strongly alkaline. The cultivated Russian sunflower, as the table shows, resists the effects of nearly 60,000 pounds of total alkali, of which 52,640 pounds was sulfate (Glauber’s salt), and 5440 common salt. This, it will be seen, is a very high tolerance, so that this sunflower, yielding such excellent poultry feed, is very widely available. Correspondingly, the “Jerusalem artichoke,” itself a sunflower, is among the available crops on moderately strong alkali soils; and so, doubtless, are other members of the same relationship not yet tested, such as the true artichoke, salsify, etc. Chicory, belonging to the same family, yielded roots at the rate of twelve tons per acre, on land of the Chino tract containing about 8,000 pounds of salts per acre.
Root Crops.—It seems to be generally true that root crops suffer in quality, however satisfactory may be the quantity, harvested on lands rich in salts, and especially in chlorids (common salt). It was noted at the Tulare substation (California) that the tubers of the artichoke were inclined to be “squashy” in the stronger alkali land, and failed to keep well; the same was true of potatoes, which were very watery; and also of turnips and carrots. It is a fact well known in Europe, that potatoes manured with kainit (chlorids of potassium and sodium) are unfit for the manufacture of starch, and are generally of inferior quality. But this is found not to be the case when, instead of the chlorids, the sulfate is used; hence the advice, often repeated by the California station, that farmers desiring to use potash fertilizers should call for the “high-grade sulfate” instead of the cheaper kainit, which adds to the injurious salts already so commonly present in lowland soils of the arid region. Such root crops are, however, available for stock feed.
The common beet (including the mangel-wurzel) is known to succeed well on saline seashore lands, and it maintains its reputation on alkali lands also. Being especially tolerant of common salt, it may be grown where other crops fail on this account; but the roots so grown are strongly charged with common salt, and have, as is well known, been used for the purpose of removing excess of the same from sea-coast-marsh lands. Such roots are wholly unfit for sugar-making.
It is quite otherwise with Glauber’s salt (sodium sulfate); and as this is very commonly predominant in alkali lands, either before or after the gypsum treatment, this fact is of great importance, for it frequently permits of the successful growing of the sugar beet; as has been abundantly proved at the Chino ranch, where land containing as much as 60,000 pounds of salts, mostly this compound, has yielded roots of very high grade, both as to sugar percentage and purity. But the analyses of the Oxnard soil show that more than 10,000 pounds of common salt will be required to render sugar beets unsatisfactory for sugar-making.
Passing to stem crops, we find that asparagus, originally itself a denizen of the sea-board, resists considerable amounts (not yet exactly determined) of common salt as well as of Glauber’s salt. It is even claimed that when grown with a dressing of common salt the asparagus is more tender and savory. But it is quite sensitive to “black alkali,” which must be neutralized with gypsum to render it harmless.
Celery did well with 13,640 pounds, of which nearly 10,000 was common salt. But with 30,000 pounds the plants were killed.
Rhubarb was a conspicuous failure, even in the weak and mostly “white” alkali lands of the Chino station tract.
Textile Plants.—Japanese hemp, while young, seemed to have a hard struggle with the alkali, but at the end of the season stood eight feet high. The ramie plant, also, will bear moderately strong alkali, apparently somewhat over 12,000 pounds per acre. Flax has not been tested in cultivation; but the wide distribution of wild flax all over the arid portions of the States of Oregon and Washington, would seem to indicate that it is not very sensitive. Another textile plant, the Indian mallow (Abutilon avicennae), was found to fail on the Chino alkali soil. But its close relative, cotton, does not seem to be specially sensitive, according to the experience had with it in the Merced river bottom in California; and its culture is extensive in Egypt, where no particular care seems to be exercised in selecting the land for the crop. It is just possible that the saline content of the soil has in California, as well as in the Atlantic sea-islands, contributed to the superior length of the fiber shown in the measurements made during the Census work of 1880.[182]
[182] Report on Cotton Culture; 10th Census of the United States, vol. 5, pp. 23 to 34.
Tolerance of Shrubs and Trees.
Grapevines.—The European grape, Vitis vinifera, is quite tolerant of white or neutral alkali salts, and will resist even a moderate amount of the black so long as no hardpan is allowed to form. At the Tulare substation it was found that grapevines did well in sandy land containing 35,230 pounds of alkali salts, of which one half was Glauber’s salt, 9,640 pounds carbonate of soda, 7,550 pounds of common salt, and 750 pounds nitrate of soda. They were badly distressed where, of a total of 37,020 pounds of alkali salts, 25,620 pounds was carbonate of soda; while where the vines had died out, there was found a total of 73,930 pounds, with 37,280 pounds of carbonate. The European vine, then, is considerably more resistant of alkali even in its worst (black) form, than barley and rye, at least on sandy land; and it seems likely that the native grapevines of the Pacific coast, californica, and arizonica, would resist even better; a point still under experiment.
Experience, however, has shown that vines rapidly succumb when by excessive irrigation the bottom water is allowed to rise, increasing the amount of alkali salts near the surface, and shallowing the soil at their disposal. Such over-irrigation has been a fruitful cause of injury to vineyards in the Fresno region, and would doubtless if practiced kill most of the vines at the Tulare substation, which are now flourishing. In such cases, sometimes the formation of hardpan is followed by that of a concentrated alkaline solution above it, strong enough to corrode the roots themselves, and not only killing the vines, but rendering the land unfit for any agricultural use whatsoever. The swamping of alkali lands, whether of the white or black kind, is not only fatal to their present productiveness, but, on account of the strong chemical action thus induced, greatly jeopardizes their future usefulness. Many costly investments in orchards and vineyards have thus been rendered unproductive, or have even become a total loss.
It should be remembered in this connection that as the roots of vines will, when unobstructed, go to depths of fifteen and even twenty feet, a subsequent rise of the bottom water from leaky irrigation ditches will drown out the ends of the deep roots and thus cause the whole root system to become diseased, inevitably resulting in unproductiveness, if not death, of the vine.
Citrus Trees.—Although the high figure of nearly 27,000 pounds for the tolerance of citrus trees, as given in the table, seems to place them rather high on the list, such high tolerance actually occurs only in very sandy soils, and when common salt is in small proportion. Generally speaking, the citrus tribe are rather sensitive to alkali salts, and more especially to common salt. In fact, as to the high tolerance-figure given in the table, observed in sandy land, the alkali there contained only a trace of common salt. Young seedling trees are particularly sensitive; so that it is often difficult to obtain a stand even when, later on, the feeding roots descend beyond the reach of injury. In the close-textured lands of Chino, young trees hardly maintained life with more than 5,000 pounds of total salts. Near Riverside, full-grown trees perished under the influence of bottom water containing 0.25%, or 146 grains of salt per gallon, which impregnated the ground; corresponding to about 9,000 pounds per acre in four feet.
In the sandy loam lands near Corona, trees eight years old suffered severely when by irrigation with alkali-water the alkali-content of the land reached 11,000 pounds per acre; as illustrated in Figs. Nos. 44, and 45. At another point in the same region, two representative trees were selected for comparison, five rows apart on land absolutely identical; one of these retained its leaves, though suffering, the other was completely leafless. The leaching of the alkali to the depth of four feet gave the following results, calculated to pounds per acre:
Sulfates. Carbonates. Chlorids. Total.
Poor tree 4,720 1,680 2,520 8,920 Better tree 4,120 2,360 720 7,200
Here it is apparently the excess of common salt to which the difference is due, and this despite the higher content of carbonate of soda in the soil bearing the better tree.
On the other hand, at the Tulare substation orange trees (sour stock) maintain vigorous growth and good bearing in a very sandy tract which to the depth of seven feet showed an aggregate content of 26,840 pounds of salts (or 22,780 to four feet depth); but which is never irrigated. (See diagram No. 66). The salts in this case consists wholly of sulfate and carbonate of soda in the ratio of fifty-four to forty-two, implying the presence of nearly 12,000 pounds of salsoda within reach of the tree roots; yet in the absence of common salt, no perceptible injury or even stress upon the trees has been noted.
According to observations made in San Diego county, Calif., lemon trees are even more sensitive to common salt than oranges, since a total content of 8,000 pounds per acre, about one-third of which was common salt, seemed to render the trees wholly unprofitable.
In view of these facts, showing that common salt is the portion of alkali by far most injurious to citrus trees, great care should be taken in the use of irrigation waters to exclude those charged with that compound; and also to avoid locating citrus orchards on land already impregnated with common salt.
The olive tree, as the table shows, is among the most resistant to alkali salts, approaching the grape in this respect. This might have been anticipated from its extended culture in the arid regions of the old world, including Palestine and northern Africa, where alkali lands abound. It is probable that the figure given in the table does not yet show the extreme limit of its endurance.
California experience with the date palm, as the table shows, credits it with an endurance not exceeding 8320 pounds of total salts. This is doubtless an underestimate, for in the Sahara desert and Egypt it is credited with being the culture which will succeed in stronger alkali than any other cultural plant; and, according to Mr. Means of the United States Department of Agriculture, it is sometimes irrigated with water containing as much as 200 grains of salts per gallon. It should be remembered, however, that these trees always grow in very sandy lands; and in the desert regions it is often grown below the surface of the ground, so as to render it wholly independent of the alkali accumulations on the surface. The extreme limit of its endurance must therefore remain in doubt until more extended experiments have made more definite data available.
Deciduous Orchard Trees.
Among deciduous orchard trees, strangely enough, the almond stands alongside of the fig in alkali-resistance, as indicated in the table. The peach seems to be much more sensitive, ranking near the apricot and prune, whose tolerance is less than half as high. That the pear and apple, generally counted among the more northern fruits in the humid region, should excel these stone fruits in endurance of alkali, is rather unexpected; and the figures concerning the whole group of these rosaceous fruits admonish us that it is unsafe to predict, without trial, what may be the outcome of culture tests. Thus plum trees, apparently in good condition, sometimes suddenly begin to fail when starting to bear; the fruit appears normal on the outside for a time, but the pit fails to form, being at times flattened out like a piece of pasteboard; and the fruit does not mature. Yet there is no observable injury to the base of the trunk, or to the roots. On the other hand, pears do well even when the outside bark around the root-crown is blackened by the action of the alkali salts. But 38,000 pounds, even of sulfate, proves too much for the pear.
The quince appears to be materially more resistant than the apple or pear. It probably ranges alongside of the fig, the soil-adaptations of which it shares in other respects also.
The English walnut resents even a slight taint of black alkali; but is fairly tolerant of “white” salts, as is shown in the peculiarly suitable light loam soils on the lower Santa Clara river, in Ventura county, as well as in Orange county, California.
Close figures for the limits of alkali tolerance in the case of deciduous orchard trees cannot easily be given or determined, owing to the difficulties inherent in the differences of root penetration in the several soils and localities; as well as the fact already alluded to, that in close-textured soils the tolerance is in general decidedly less than in sandy lands. Hence the figures in the table must be taken as more nearly representing relative tolerances, rather than absolute data to be applied in every case. As regards the stone fruits, it should be remembered that the Myrobalan root, being at home in Asia Minor, where alkali abounds, should when practicable be used wherever alkali conditions exist, in preference to all but the almond, which seems to resist well, even on its own root, but has not as wide a range of adaptations as a grafting stock as the myrobalan. While most of the other stone fruits at the Tulare substation were on myrabalan roots, the stock of those in outside orchards was mostly in doubt. It is also to be kept in mind that different varieties of the same fruit—e. g., pears and apples—show a not inconsiderable variation in their resistance.
Timber and Shade Trees.
Of trees, forest and shade, suitable for alkali lands, some native ones call for mention. One is the California white or valley oak (Quercus lobata), which forms a dense forest of large trees on the (almost throughout somewhat alkaline) delta lands of the Kaweah River in California, and is found scatteringly all over the San Joaquin Valley. Unfortunately this tree does not supply timber valuable for aught but firewood or fence posts, being quite brittle.
The native cottonwoods, while somewhat retarded and dwarfed in their growth in strong alkali, are quite tolerant of the white salts, especially of Glauber’s salt. As they usually grow near to the water, their tolerance for alkali salts is difficult to ascertain.
Of other trees, the oriental plane, or sycamore, and the black locust have proved the most resistant in the alkali lands of the San Joaquin Valley; and the former being a very desirable shade tree, it should be widely used throughout the regions where alkali prevails more or less. The ailantus is about equally resistant, and but for the evil odor of its flowers, deserves strong commendation.
Of the eucalypts, the narrow-leaved Eucalyptus amygdalina (one of the “red gums”) and the closely related viminalis, seem to be least sensitive, and in some cases have grown in alkali lands as rapidly as anywhere. The rostrata, as well as the pink flowered variety of sideroxylon, are now doing about as well as the amygdalina at Tulare, where at first they seemed to suffer. The common blue gum, globulus, is much more sensitive.
Of the Acacias, the tall-growing A. melanoxylon (“black acacia”) resists pretty strong alkali, even on stiff soil; as can be seen at Tulare and Bakersfield, California, where there are trees nearly two feet in diameter. The beautiful A. lophantha (Albizzia) has in plantings made along the San Joaquin Valley railroad shown considerable resistance, likewise; but it is quite sensitive to frost.
Of other Australian trees, one of the Australian “pines,” (Casuarina equisetifolia), is doing well on fairly strong alkali land in the San Joaquin Valley.
A remarkably alkali-resistant shrub or small tree is the pretty Kœlreuteria paniculata from China, which at Tulare is growing in some of the strongest alkali soil of the tract. Unfortunately it is available mainly for ornamental purposes; its wood, while small, is very hard and makes excellent fuel.
Of trees indigenous to the Atlantic and East Central United States, the Tulip tree, the Linden, and most other trees of the humid region, including the English oak (Quercus pedunculata) become stunted in alkali soils. The honey locust, being particularly adapted to calcareous lands, does moderately well on alkali lands, but its thorns and imperfect shade render it not very desirable. The black locust and the elms have on the whole done best. The eastern maples are not successful; but the California maple (Acer macrophyllum) and the box elder (Negundo californica) have done fairly well in the lighter alkali lands of the San Joaquin Valley.
The Conifers—Pines, firs, cedars, cypress, etc., are very sensitive to black alkali and will not endure much even of the “white” salts. Even the native juniper of the mesas carefully adheres to the portions—breaks and upper slopes, hilltops, etc.—which are more or less leached by the scanty rains of these regions.
INDUCEMENTS TOWARD THE RECLAMATION OF ALKALI LANDS.
The expense involved in the reclamation of strong alkali lands naturally gives rise to the question whether adequate advantages are likely to be derived from such expenditure; specially when the last resort—underdraining and leaching—has to be adopted.
Those familiar with the alkali regions are aware how often the occurrence of alkali spots interrupts the continuity of fields and orchards, of which they form only a small part, but enough to mar their aspect and cultivation. Their increase and expansion under irrigation frequently renders their reclamation the only alternative of absolute abandonment of the investments and improvements made, and from that point of view alone it is of no slight practical importance. Moreover, the occurrence of vast continuous stretches of alkali lands within the otherwise most eligibly situated valley lands of the irrigation region forms a strong incentive towards their utilization.
There is, however, a strong intrinsic reason pointing in the same direction, namely, the almost invariably high and lasting productiveness of these lands when once rendered available to agriculture. This is foreshadowed by the usually heavy and luxuriant growth of native plants around the margins and between alkali spots (see fig. 60); i. e., wherever the amount of injurious salts present is so small as not to interfere with the utilization of the abundant store of plant-food which, under the peculiar conditions of soil-formation in arid climates, remains in the land instead of being washed into the ocean. Extended comparative investigations of soil composition, as well as the experience of thousands of years in the oldest settled countries of the world, demonstrate this fact and show that so far from being in need of fertilization, alkali lands usually possess extraordinary productive capacity whenever freed from the injurious influence of the excess of useless salts left in the soil in consequence of deficient rainfall. (See analyses, chapter 22, pp. 436, 437).
Among many striking examples of the results of such reclamation, is that represented in the annexed figure (75), of grain grown on strong alkali land, before and after reclamation treatment. On the original land even “alkali weeds” would hardly grow; while afterward a wheat crop representing forty-two bushels per acre was grown. Additional illustrations are shown in the second figure (76), showing crops of wheat and barley as grown on partly reclaimed land at the Tulare substation.
While it is certainly true that when rightly treated, alkali lands can be rendered profusely and lastingly productive, yet close attention and constant vigilance are needed so long as the salts remain in the soil; and no one not determined to give such land such full attention, should undertake to cultivate it.
PART FOURTH.
SOILS AND NATIVE VEGETATION.
XXIV. [183]
THE RECOGNITION OF CHARACTER OF SOILS FROM THEIR NATIVE VEGETATION; MISSISSIPPI.
Climatic and Soil-Conditions.—Next to climatic conditions, chief among which are temperature and moisture, the physical and chemical nature of the soil and subsoil is the most potent factor in determining the natural vegetation of any region. The limitations we observe in the adaptation of cultivated lands to certain crops, even with artificial help, must be much more strongly pronounced when no such aid is given, and the struggle for the survival of the fittest is continued, subject only to seasonal variations, for thousands of years. It is obvious that within the limits of the regional flora, the natural vegetation of any tract represents the best adaptation of plants to soils, in the results of long periods of the struggle for existence between competing species; the survivors being those best adapted to the entire environment.
[183] The special object of this chapter as a whole has seemed to the writer to require a repetition of much that is already said in the preceding chapters.
In countries uninhabited by man the chief conditions outside of the direct influence of climate and soil that may materially affect the results of the competition are connected with the animal creation; and within the latter, insects are probably the most influential, beneficially in the part they play in the fertilization of flowers, injuriously in their role as parasites. Since in the absence of man, the effects of fire would ordinarily be conditioned upon the occurrence of thunderstorms, its effects would then properly come under the head of climatic influences. But while these and some other disturbing factors must not be forgotten in considering the relations of soils to the natural vegetation borne by them, the common consensus of mankind has long recognized the intimate connection existing between the two, and has everywhere made it the basis of at least a general estimate of the agricultural value of the land concerned.
NATURAL VEGETATION THE BASIS OF AGRICULTURAL LAND VALUES IN THE UNITED STATES.[184]
In countries long settled, as in Europe, where the nature of the original forest is unknown or a matter of tradition only, the adaptations of the several kinds of land to culture plants and forest trees has been gradually ascertained by cultural experience, and their designations, values and uses determined accordingly. In the United States, the character of the original forest growth is mostly in evidence, or is definitely known by tradition, even in the older states. West of the Alleghenies, there is as yet little difficulty in this regard, partly because even where the original forest growth has disappeared its character remains on record, the assessed land values being very commonly based upon the tree growth of the wild land. In the Southern States especially, the classification of uplands into “pine lands” and “oak lands” is universal, and is associated with certain limits of valuation, both by assessors and purchasers. Within each of these two classes, however, there are well-defined gradations of cultural value according to the kind (species) e. g., of pine or oak that occupies the ground, either alone, or in intermixture with other trees whose presence or absence is considered significant. In the case of “bottoms” or alluvial lands, corresponding distinctions and classifications obtain; we hear of hickory, beech, gum, and cherry bottoms, hackberry hammocks, etc. each name being associated with certain cultural values or peculiarities of soil, well understood by the farming population.
[184] See above, pp. 313 to 315, chapter 18.
INVESTIGATION OF CAUSES GOVERNING THE DISTRIBUTION OF NATIVE VEGETATION.
It seems singular that such well and widely understood designations and important distinctions should not long ago have been made the subject of careful investigation and precise definition by agricultural investigators. For apart from their practical importance as guides to the purchaser of land, or settler, this correlation of land-values and natural vegetation is of the utmost interest in offering an opportunity for researches on the factors which determine the choice of these several trees and the corresponding shrubby and herbaceous growths. Moreover, the cultural results and adaptations corresponding to certain natural growths being known from experience, a thorough knowledge of the soils so characterized should enable us to project into new lands, where experience is lacking, the benefits of experience already had; even in cases where, from some cause, the natural vegetation is different, or absent. Only very fragmentary and casual observations in this line are on record thus far, almost the only generally recognized chemical characterization of plant habit being that of calciphile (lime-loving), and calcifuge (lime-repelled) ones, but with few attempts at more than local application. Yet, to ascertain by the physical and chemical examination of soils what are determining factors of certain natural vegetative preferences, which are invariably followed by certain agricultural results, should not be an unsolvable problem, and its practical importance should justify its most active investigation.
Investigations in Mississippi.—In his explorations connected with the Geological and Agricultural Survey of the State of Mississippi, as well as, later on, in similar researches carried on in other states, the writer was forcibly struck with the close correspondence of the limits of geological formations with those of vegetative zones; so much so that he was led to rely very largely on the latter as indicative of the probable occurrence of outcrops that otherwise, in a level country, would have passed unperceived.
These observations upon the correlations between virgin soils and their native vegetation having originally been made by the writer, in great detail, in the state of Mississippi, from 1855 to 1872, and that state being from natural causes a peculiarly cogent illustration of such correlation: it seems advisable to describe first, somewhat in detail, the facts observed there, and subsequently to compare them with what has been observed elsewhere by him or others.
No claim is made to an even approximately exhaustive presentation of the whole subject, even within the United States; nor is it intended to give complete lists of vegetation.[185] The object is to give such facts as have been fairly well established by observation, hoping that more thorough investigations in the same line will thereby be stimulated.
[185] Such lists, so far as the State of Mississippi is concerned, may be found in the writer’s Report on the Agriculture and Geology of Mississippi, 1860. See also Plant Life of Alabama, by Charles Mohr.
VEGETATIVE BELTS IN NORTHERN MISSISSIPPI.
The diagram below is a sketch-map of the most northern part of Mississippi, showing the narrow parallel belts of successive geological formations or terranes running north and south, which bear the varying zones of vegetation characteristic of each one, as indicated in the legend beneath.
SOIL REGIONS OF NORTHERN MISSISSIPPI, SHOWING CHANGES FROM EAST TO WEST, AND LIME PERCENTAGES IN SOILS.
|Lime, p.c.| Soil Character.| Vegetation. | | | 1. | .40— .60|Clay loams, clay. |Oaks, sweet gum, tulip tree, | | | walnut, red cedar, ash, | | | hickories. | | | 2. | .05— .14|Sandy loams, sands.|Short-leaf pine, post, scarlet | | | and black-jack oaks, black gum, | | | chestnut. | | | 3. |1.00—1.40|“White lime” |Red cedar, crab-apple, Chickasaw | |prairie; clays and | plum, sturdy post and black-jack | |clay loams. | oaks, honey locust. | | | 4. | .30— .50 |Mellow red loams of|Oaks, hickories, walnut, tulip | |“Pontotoc ridge.” | tree, ash, cherry, umbrella | | | tree. | | | 5. | .08— .18 |Heavy gray clay |Scrubby post and black-jack oak, | |soils, some gray | short-leaf pine. | |sands. “Flatwoods.”| | | | 6. | .15— .25|Sandy ridges and |Post, black-jack, scarlet and | |uplands, broken. | upland willow oaks, small; some | | | chestnut. | | | 7. | .25— .35 |Mellow clay loams |Fine black, red, post, Spanish | |of “Table lands.” | and black-jack oaks, hickories, | | | sweet gum. | | | 8. |2.00—5.00|Calcareous sandy |Oaks as above, tulip tree, ash, | |silt, “Bluff loess”| honey locust, linden, sassafras, | |“Cane Hills.” | umbrella tree, cane. ---+----------+-------------------+--------------------------------- 9. | .40—1.10 |Mississippi Bottom.|Basket, white and black oaks, | | | ash, tulip tree' 9a.| 1.12— |Yazoo backland |honey locust, pecan, shell-bark | |buckshot clay. | hickory, walnut, hackberry, | | | cane. 9b.| .40 |Sandy alluvium, |Sweet gum, maple, willow oak, | |“Frontland.” | elm, hackberry. ---+----------+-------------------+--------------------------------- 10.| .26— .40 |Light sandy loam of|Dogwood, sweet gum, holly, ash, | | “Dogwood ridge.” | sassafras, prickly pear. | | | ---+----------+-------------------+---------------------------------
Limestone Belt.—beginning on the east we have, first, a narrow belt of limestones of the carboniferous formation, on which there is a fine growth of various oaks, with walnut, hickory, sweet gum, tulip tree and red cedar, and a very productive soil.
“Pine Hills.”—Next adjoining on the west comes a belt of sandy, non-calcareous beds of the lower Cretaceous formation, about 18 miles wide. It has a hilly surface, and outside of the narrow valleys, the prevalent timber is short-leaved pine and scrubby black-jack oak, with some post oak and small black gum, and a few large chestnut trees.
“Prairie” Belt.—Westward of this belt we descend into a level “prairie” region, six to twelve miles wide; the “white lime country,” having heavy black clay soils, underlaid by the cretaceous “rotten limestones;” which are profusely productive. The sparse tree growth consists of stout, vigorous and dense-topped post and black-jack oaks, with clumps of crab-apple, Chickasaw plum thickets, and an occasional red cedar.
Pontotoc Ridge.—West of the prairie belt we ascend into a ridgy hill country, twelve to fourteen miles wide; the “Pontotoc ridge,” formed of the soft limestones and marls of the upper cretaceous formation, and covered with a deep red soil, which bears a rich growth of oaks, with hickory interspersed, and black walnut, umbrella and tulip tree even on the ridges. This is one of the finest agricultural regions of the State.
Flatwoods.—From the Pontotoc ridge and its fine lands and timber we descend to westward into the “Flatwoods” belt, three to eight miles wide; a level country underlaid by heavy gray non-calcareous clays of the tertiary formation, from which most of its soil is directly formed. It bears a pretty dense growth of the same species of oaks that characterize the prairies farther east, but the form, habit and size of the trees is so different that many of the inhabitants believe them to be different species. The black-jack oak looks like small, dense-topped apple trees; the post oak, on the contrary, has an open top of the form of a short-handled, spreading broom. The soil is poor and unthrifty, as are the few disappointed settlers, who bought the land on the strength of its oak-tree growth. (See page 500).
Brown Loam Region. Table Lands.—Adjoining the Flatwoods on the west is a broad upland region, with a brownish-yellow soil and subsoil, extending nearly to the edge of the Mississippi bottom. In its eastern portion it is rather broken and hilly, with sandy ridge soils, a mixed growth of oaks and short-leaved pine, and occasional chestnuts; a fair farming country only. To westward the ridges become lower and broader, assuming a plateau character. The pine disappears, and black, Spanish, red and white oak, with much hickory, largely replaces the black jack and post oak; thus characterizing the fertile brown-loam “table-lands” that extend through western Tennessee and Mississippi into Louisiana, and have long been noted for their high production of fine upland cotton.
Cane Hills.—On the western border of the table-land region, and here forming a strip only a few miles wide along the edge of the Mississippi bottom, but from 70 to 450 feet above it, lies the remnant of what farther south constitutes a wide and important agricultural belt; the Bluff or Loess formation, locally known as “the Cane Hills.” The soil is largely composed of grains of sand and silt cemented by lime carbonate; it is therefore calcareous, and as on the Pontotoc ridge, described above, we find here the black walnut, the tulip tree, ash and others, elsewhere restricted to the alluvial “bottoms,” on the ridges themselves, from sixty to a hundred feet above the stream beds.
Mississippi Bottom.—At the western foot of this bluff there lies the great Mississippi Bottom, with its rich soils and varied forest growth. This also, however, subdivides into at least three distinct soil and vegetative zones, viz., the sandy “Frontlands,” which lie on the immediate banks of the great river and its main branches, and the heavy clayey “Back-land” areas, whose soils are partly the product of modern swamp deposits from backwaters, partly result from the disintegration of strongly calcareous clays constituting the lower part of the Bluff or Loess formation. A third natural subdivision is the “Dogwood ridge,” a narrow belt of slightly elevated land, mostly above ordinary overflows, which extends diagonally from the Mississippi river to the Yazoo bottom, and seems to be the continuation of “Crowleys ridge” in Arkansas. Each of these soil belts has its own characteristic forest growth, as indicated in the table below the map.
We have here along an east-and-west line of about 200 miles, eleven markedly distinct zones of vegetation, readily recognized as such by every farmer, and each underlaid by a distinct geological terrane. It does seem as though a close study of these and of the soils overlying them should lead to some definite results showing the physico-chemical causes of these differences.
Lime apparently a governing Factor.—The connection of some of these changes in vegetation with the calcareous nature of the corresponding formation has already been referred to. As regards four of the eleven divisions, this is obvious even to the casual observer, and is well known to the population, who speak of the “lime country” or belts being, as a matter of common knowledge, the best land; in full accord with what, in Kentucky and elsewhere, has passed into a popular maxim.[186]
[186] “A lime country is a rich country.”
Taking as a guide the trees and plants which characterize the obviously calcareous lands, our next step should be to verify, if possible, the fact that wherever these occur naturally, lime is abundant in the soil in comparison with those lands in which such vegetation does not occur naturally, or perhaps even fails to flourish when planted without special fertilization. This the writer has sought to do, first in connection with the survey work of the state of Mississippi, and subsequently in the wider field that has since come under his observation.
SOIL BELTS IN SOUTHERN MISSISSIPPI.
In Mississippi, the general conclusions derived from the observations made on the northern cross section, are corroborated many times over in other portions of the state. Aside from the cretaceous prairie region, there runs across the middle of the state a belt of varying width, of calcareous tertiary beds, which also give rise to more or less extensive tracts of “black prairie” lands, interspersed with non-calcareous, mostly sandy ridges, the lower slopes of which, influenced by the calcareous beds, bear an oak and hickory growth, while the higher portions have only pine, and usually remain uncultivated. Southward of this “central prairie” belt lies the long-leaf-pine forest area of the state, underlaid throughout by sandy, non-calcareous formations, with poor sandy soils, save here and there in patches, which can be at once recognized by the replacement of the long-leaved pine by a vigorous oak growth; as is also the case where the pine area abuts against the calcareous “Cane Hills” on the west. The bottom soils of this region are largely “sour,” and bear the gallberry (Prinos glaber), bay galls (Persea Carolina), ti-ti (Cliftonia monophylla), candleberry (Myrica cerifera), various whortle-berries, the pitcher plants (Sarracenia), yellow star grass (Aletris), sundews, Xyris, Eriocaulon, and other plants of similar habits.
Vegetative and Soil Features of the Mississippi Coast Belt.—South of the long-leaf pine area lie the coast flats, with sour, sandy soils underlaid by stiff clays. On these “pine meadows” of the Mississippi coast occur some of the most striking cases of modifications of vegetation due to physical and chemical causes.
As is well known, the long-leaved pine habitually belongs to the dry sandy uplands of the Gulf States; the deciduous cypress, on the other hand, is most characteristic of the swamps, where its roots are permanently submerged in water. But on the pine meadows of the Mississippi coast we see these two incongruous trees growing side by side, though sadly worsted by their mutual concessions; their heights usually ranging from 12 to 15, rarely as much as 18 feet.[187] Yet both preserve their characteristic forms, the cypress being an exact miniature reproduction of the usual level-topped swamp form, except as to the “knee” feature; while the pine differs only in stature from its giant brethren of the pine hills, from which it can be traced down through all grades of transition. The soil on which this growth occurs is a sour, sandy one, one and a half to three feet in depth, underlaid by a solid, impervious gray clay, above which is usually found several inches of coffee-colored bottom water, which drains slowly into the sluggish water-courses, themselves carrying brownish, sour, but very clear waters. Analysis shows the soil to be sour and extremely poor, especially in its lime and phosphates (see chapter 19, p. 352); its herbaceous vegetation consists exclusively of very small-seeded, “calcifuge” plants (sedges, orchids, Juncus, Hæmodoraceæ, Xyris, Polygala, etc.). This land is wholly unproductive and affords but indifferent pasturage, except the first season after burning-over; probably because of the effect of the minute amount of ashes so added. As the coast is approached, the clay subsoil has an increasing depth of sandy soil-mass above it, and on these “sand hammocks” the long-leaved pine gradually assumes more and more of its usual stature; the cypress disappears, and the Cuban pine (here called pitch pine) gradually comes in; while the sedgy vegetation diminishes and finally disappears. On this land crops may be grown as in the long-leaf-pine uplands.
[187] R. M. Harper, who has graphically described the vegetative features of the coastal plain of Georgia (Contr. from the Dep. of Bot. Colum. Univ. Nos. 192, 215, 216, 1902-05; also Bull. Torr. Bot. Club 29-32), claims the deciduous cypress of the wet pine-barrens and ponds therein, the vegetation of which greatly resembles that of the pine meadows of the Mississippi sea-coast, to be a distinct species, Taxodium imbricarium, the leaves of which are imbricated, instead of two-ranked and with spreading leaflets. He supports this distinction mainly by the differences in habit from the Louisiana swamp cypress, and the fact that the imbricated form occurs wholly on non-calcareous land, while the other is at home in the calcareous alluvial areas. The imbricated form has been observed and commented on before, as a mere ecological variation, and in the writer’s opinion this is all that can be claimed, in view of the much greater differences in the form of other trees, notably oaks, illustrated below, caused also by lime. There would, à fortiori, be reason for claiming at least three different species of post oak and black-jack (and two of willow oak), which differ not only in tree form but also in the form and number of leaf lobes, and yet can be traced into one another by innumerable transition forms. If new species are to be established on such grounds, it is hard to see where the variations manifestly due to environment are to come in.
But on the immediate coast, evidently under the influence of the aboriginal “shell mounds,” the yellow sandy soil becomes blackish from the (humus-forming) effect of the lime thus supplied; and concurrently the coast live-oak (Q. virens), grape vines, the Hercules club (Aralia spinosa), “l’herbe a trois quarts” (Verbesina sp.), and numerous leguminous plants (which are wholly absent from the pine meadows) take possession of the land, which is very productive and has been specially utilized in the growing of Sea Island cotton. Here the clay stratum is 15 to 20 feet below the surface, and roots penetrate to great depths in the pervious soil, whose great thickness makes up for its low percentage of plant-food (see table below). This land is distinctly limited by the extent of the shell heaps, past or present, and shows a respectable percentage of lime.
The annexed schematic profile (fig. 78) illustrates these changes of soil and vegetation, which furnish a striking example of the effective modification of vegetative features by physical and chemical soil-conditions.
It would be difficult to find a more striking exemplification of the effect of lime carbonate, not only upon the vegetation but also upon the physical and chemical characters of the hopelessly unproductive soil of the sand hammocks and pine meadows; no longer brown and sour, but jet black and neutral, modifying favorably every physical quality. Humus likewise nowhere shows its benefits more strikingly.
Table of Lime-Percentages.—The table below shows the average lime percentages observed in most of the several vegetative areas mentioned above. To meet the objection sometimes made that the vegetative changes noted may be due to the larger amounts of phosphoric acid and potash frequently found in calcareous lands, the percentages of the latter are also given. Considering the origin of limestones, such a connection is not unexpected, but it is far from constant. On the contrary, the frequent co-occurrence of much lime and high production with small percentages of phosphoric acid and potash leads to the conclusion, already discussed (see chapter 19, p. 365), that in presence of abundance of calcic carbonate, smaller percentages of phosphoric acid may be considered adequate than when lime is deficient, on account of greater availability. Almost the same may be said of potash; and it is quite possible that the presence of large amounts of lime tends to prevent the leaching-out of this base, in consequence of greater facility for the formation of zeolites. Illustrations of this kind have already been given (chapters 3, 22).
Definition of “Calcareous Soils.”—It will be noted that the very obvious and important changes of vegetation are brought about by comparatively slight differences in lime-content. In fact, only two of the soils enumerated above would, according to the estimates usually given in books on soil composition, be considered as properly calcareous. But the decisive feature in this matter must evidently be the native vegetation, which expresses the nature of the land much more clearly and authoritatively than any arbitrary definition or nomenclature can possibly claim to do. A soil must be considered as being calcareous whenever it naturally supports the vegetation characteristic of calcareous soils.
TABLE SHOWING NATIVE FOREST GROWTH, POPULAR ESTIMATE OF DURABILITY AND INITIAL PRODUCTION, AND PERCENTAGES OF LIME, PHOSPHORIC ACID AND POTASH, IN MISSISSIPPI LANDS. ===+==========+============================+======================= No.| Name. | Natural Vegetation. | Production Per Acre. | | | ---+----------+----------------------------+----------------------- | Black |Mainly sturdy black-jack and|400 lbs. cotton lint, 172| Prairie | post oak, red cedar, crab | decreasing to 200 lbs. | Soil. | apple and honey locust. | in 30 years. | | | ---+----------+----------------------------+----------------------- | Pale |Scarlet, post and Spanish |200 lbs. cotton first 164| Yellow | oak, small. | year, tailing off | Ridge | | to 75 to 100 lbs. | Loam. | | by 5th year. ---+----------+----------------------------+----------------------- | Pontotoc |Oak, hickory, walnut, sweet |350-400 lbs. cotton 226| Ridge |and black gum, honey locust.| lint, 300 lbs. after | Soil. | | 20 years. ---+----------+----------------------------+----------------------- | Heavy |Post and black-jack oak, |20 bushels of corn 230| Flatwood | and some short-leaved pine.| first year--then | Soil. | | nubbins only. ---+----------+----------------------------+----------------------- |Black-Jack|Black-jack oak, pine, |Unproductive. 345| Ridge | huckleberry. | | Soil. | | ---+----------+----------------------------+----------------------- | Oak and |Red and post oak, pig-nut |200 lbs. cotton lint | Pine | hickory, short-leaved pine.| at first; 100 lbs. 142| Upland | | 6-8 years. | Loam. | | ---+----------+----------------------------+----------------------- | Brown |Black, post, Spanish and |400 lbs. cotton--250 219|Table-land| black-jack oak, hickory, | lbs. after 20 years. | soil. | sweet and black gum. | ---+----------+----------------------------+----------------------- | Bluff or |Cane, black and white oak, |400 lbs. cotton, 237| Loess | tulip tree, linden, | decreasing to 250 lbs. | Soil. | sassafras. | after 30 years. ---+----------+----------------------------+----------------------- |“Buckshot”|Hickory, ash, sweet gum, |800 lbs. cotton lint, 390| Soil. | pecan, cow oak, honey | reduced to 500 lbs. | | locust, cane, crab-apple, | in 30 years | | plum. | cultivation. ---+----------+----------------------------+----------------------- | Pine |Long-leaved pine, with |20-30 bushels corn for 206| Hill | scarlet and post oak, | one year--then | Soil. | scattered small and | nubbins. Usually | | occasional pig-nut | good sweet potatoes | | hickory. | for 2-3 years. ---+----------+----------------------------+----------------------- | Pine |Dwarf long-leaved pine, |Unproductive. Bears 215| Meadow | cypress, sedges, orchids, | small-seeded “sour” | Soil. | Hæmodoracæ, etc. | vegetation. ---+----------+----------------------------+----------------------- | Shell |Live and water oak, cedar, |300 lbs. sea-island 88| Hammock | magnolia, holly, dogwood, |cotton for 15 years. | Soil. | sweet gum, hickory, | | | sassafras, grape, Hercules | | | club, etc. | ---+----------+----------------------------+-----------------------
===+==========+===============+=======+=====+=====+======+======= No.| Name. | Physical | K₂O. | CaO.| MgO.| P₂O₅.| Humus. | | Character. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Black |Heavy adhesive | | | | | 172| Prairie | dark-colored | .333 |1.367| .363| .104 | 1.25 | Soil. | clay. | | | | | | | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pale | Pale yellow | | | | |★ 164| Yellow | sandy loam. | .093 | .069| .126| .033 | .50 | Ridge | | | | | | | Loam. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pontotoc | “Mulatto” | | | | | 226| Ridge | medium loam. | .374 | .281| .234| .082 | 1.00 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Heavy | Heavy gray | .753 | .178| .831| .052 | .305 230| Flatwood | clay. | | | | | | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- |Black-Jack| Very sandy | | | | |★ 345| Ridge | loam. | .073 | .142| .100|Trace.| .20 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Oak and | Medium | | | | | | Pine | loam. | | | | |★ 142| Upland | | .236 | .092| .196| .091 | .50 | Loam. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Brown | | | | | | 219|Table-land| Clay loam. | .630 | .270| .450| .210 | .79 | soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Bluff or | Sandy loam. | .511 |5.921|3.278| .143 | .72 237| Loess | | | | | | | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- |“Buckshot”| Heavy | | | | |★ 390| Soil. | calcareous | 1.104 |1.349|1.665| .304 | 1.0 | | clay soil. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pine | Light sandy | | | | | 206| Hill | loam; mere | .259 | .129| .180| .030 | .35 | Soil. | sand at | | | | | | | 3 feet. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pine | Very sandy | | | | | 215| Meadow | loam, gray | .061 | .023| .069| .021 | | Soil. | clay subsoil. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Shell | Very sandy | | | | | 88| Hammock | loam, deep. | .080 | .115| .065| .107 | .75 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- Starred values (★) are approximate.
DIFFERENCES IN THE FORM AND DEVELOPMENT OF TREES.[188]
It will be noted that in the above table, as well as in the discussion preceding it, identical species of trees are ascribed to vegetative areas of widely different productive capacity. Perhaps the most striking example is that the cretaceous prairies and the adjoining flatwoods belt, standing respectively highest and lowest in the scale of productiveness, are yet bearing specifically identical tree-growth, to-wit, the post oak (Quercus minor) and the black-jack oak (Q. marylandica). While to the field botanist[189] there can be no question as to the absolute specific identity of the two trees as growing on the respective areas, yet the mode of development of both is so different in the two cases, that, as before remarked they are popularly supposed to be different “kinds.”
[188] It is a matter of regret to the writer that owing to the long distance intervening and the difficulty of securing competent and sympathetic observers for such work, it has not been possible for him to secure photographs of the tree-forms here discussed. At the time his own observations were made, photography was practically unavailable as yet, and the figures given are therefore based upon sketches made at the time, and partly upon recollection. They represent types rather than definite individuals, which were however described when fresh in mind, in the Report on the Agriculture and Geology of Mississippi, 1860, pages 254 et seq.
[189] It has been already, and doubtless will be again and increasingly, attempted to make distinct “species” of these widely different forms of trees. But this is simply begging the question. Mere external diagnostic marks will not avail here; it would have to be shown that the seed of these different forms do not produce the other forms under changed conditions. Until this has been done, the number-less transition forms which he that runs may observe in the field, throw upon the species-makers the onus of proof of differences of specific value—if it be possible to define such value.
Forms of the Post Oak.—The post oak of the prairie lands is a tree 50 to 70 feet high, with a stout, excurrent, rather conical trunk, often somewhat curved to one side above, and densely clothed from within 12 or 15 feet of the ground with comparatively short, sturdy branches set squarely to the trunk, much crooked (geniculate), often reflexed downward; altogether forming a dense head, beneath whose thick foliage, a bird or squirrel is quite secure from the hunter’s aim.—In the flatwoods, on the contrary, the post oak has a thin, rather short trunk, divided up at 15 or 20 feet height into long, rod-like branches, spreading broom-fashion, and scantily clothed with short twigs bearing tufts of leaves; thus forming an open head, in which no creature can hide effectually. On the brown-loam table-lands, again, the post oak has a straight, rather slender, excurrent trunk with long and more or less crooked limbs projecting at a large angle, sometimes even drooping, and freely divided up into lateral, leafy branches; the trees attain from 40 to 55 feet in height. Again, on the high sandy ridges which are interspersed in the eastern portion of the brown loam area, we find, generally associated with a similarly depauperated form of the black-jack oak, and with the Upland Willow oak (Q. cinerea), a form of the post oak intermediate between that of the Flatwoods and the Table lands; twelve to fifteen feet high, with thin trunk, “sprangling” long, crooked branches, clothed with sparse tufts of leaves. These four strikingly distinct types are shown schematically, in their extreme development, in the subjoined figures.
It is hardly necessary to say that between these extreme forms there are many degrees of transition, corresponding to the transitions between the several soil-classes respectively represented by them; or they may be developed into depauperated types. Thus, for example, the forms of the post and black-jack oak found on the sandy ridges of the yellow loam region, hardly need experience in the observer to interpret them as characterizing a wretchedly poor soil.
Forms of the Black-jack Oak.—Not less striking are the characteristics of the forms of the black-jack oak as developed upon these several kinds of land. The black-jack of the prairies is a low tree with a dense rounded head, often somewhat flattened above, and a low, thick-set trunk divided up into square-set branches, so densely clad with foliage that no light penetrates into the interior, and birds can safely hide and nest within it. The height rarely exceeds 35 feet, the head being 20 to 30 feet across.
The Flatwoods form, on the contrary, rarely exceeds 15 feet in height, with a very rough bark and a small, rather dense, rounded top, giving the whole the appearance of a small apple tree. Practically the same form is seen on poor, clay ridges of “hog-wallow” land.
On the brown-loam lands the black-jack, like the post oak, has a rather slender, often somewhat crooked, but excurrent trunk 35 to 50 feet high, with more or less crooked limbs of moderate length, well provided with leafy branches, but forming altogether a rather open crown. A depauperated form of this type occurs on the sandy ridges of the yellow-loam region and is 12 to 15 feet high, with slender, crooked branches, clothed with scanty foliage; as shown in Figure No. 80, alongside of the other typical forms.
In all these variations of the tree forms, there is also a concomitant variation in the forms and other characters of the leaves. Thus in the compact forms of the black-jack oak, the trilobate leaf is almost completely obliterated, the leaf being simply rounded-cuneate, somewhat auriculate at base. In the sparse-branched upland forms the leaves are deeply three-lobed, and the ferruginous tomentum of the lower surface is much less pronounced. The lobation of the post oak also varies considerably both in the numbers of lobes and in their obtuseness. Similar differences prevail in the case of the black and Spanish oaks; thus in the latter, the long terminal, falcate lobe is always most pronounced on “rich” soils, while on poor ones the trilobate leaf predominates.
Of course all these forms may be found bearing acorns, so that they undoubtedly represent adult trees.
Characteristic Forms of other Oaks.—Similar general features are repeated in the case of the other species of oaks, and also more or less in other kinds of trees; though mostly less pronouncedly than with the two species above described. Among the more striking are the two forms of the willow oak (Q. phellos), which on low, undrained ground assumes the low, rounded, “apple-tree” form, while on well-drained uplands of good fertility it is a beautiful, slender tree producing almost the effect of the acacia type; it is then a sign of first-class land. The scarlet oak rather reverses these types; on good, “brown-loam” upland it is of rounded form, not very tall, with sturdy, rough-barked trunk; while on poor hillside lands its tall, smooth, white trunk stands out as a conspicuous admonition to the land-seeker to beware of a poor purchase. The black and Spanish oaks also indicate, by tall thin trunks, a deterioration of the land as compared with the lower and more sturdy growth on areas relatively richer in lime.
Sturdy Growth on Calcareous Lands.—One feature invariably repeated, not only in Mississippi but throughout the United States, is that in many strongly calcareous soils the growth of all trees, as well as of shrubs and of many herbaceous plants, is of a more sturdy and thick-set habit than that of the same species grown on thin, sandy, or generally on non-calcareous land. This effect is quite as apparent in the arid region of the Pacific Coast as in the Atlantic States, on the prairies of the Middle West, and of the Gulf Coast. The experienced farmer recognizes this habit of the tree-growth as a sign of good land, and the reverse, viz., trees of lank, tall and thin growth, as evidence to the contrary, from the Atlantic to the Pacific.
Cotton Plant.—The cotton plant affords very striking evidences of this influence of lime. On the bottom lands of a creek in Rankin county, Mississippi, the writer found a “patch” of cotton with luxuriant stalks reaching above the head of a man on horseback, but almost devoid of “squares” or blooms. The soil was very dark and rich-looking, but was derived from a non-calcareous tertiary terrane surrounding the heads of the stream. A few rods below, the latter crosses the line of a calcareous terrane, from which copious marly debris have been washed down on the bottom soil. Here the cotton was just half as high as above, and thickly covered with squares, blooms, and bolls.
Another similar example was noted on the Chickasawhay river, in Wayne county, Miss. Where that stream flows through the non-calcareous, lignitiferous area of the tertiary formation, its bottom lands bear cotton crops of medium productiveness only, the stalks being of the usual height of about three feet, and only fairly bolled. But a short distance below the point where the soft marls of the marine tertiary are cut into by the stream, the cotton plants on the bottom lands are from 18 to 20 inches high only, closely branched, and literally thronged with cotton bolls, so that the fields appear a solid mass of white. The only objection urged against this land is that to pick such cotton “breaks the backs” of the pickers. The tree growth of the bottom, of course shows a corresponding change.
Lime Favors Fruiting.—In connection with the obvious changes of form and stature caused by the presence of an abundant supply of lime carbonate in soils, there is another that has been long noted in cultivation, but is no less striking in the native vegetation. The abundant fruiting of oaks on such lands as compared with the same species on non-calcareous soils is a matter of common note in the Mississippi Valley states; and the same is true of other trees, and of herbaceous plants as well. The fruit on the lime soils is often smaller, unless much humus is present; but the statement made in Europe that cultivated fruits, and especially grapes, are sweeter on calcareous lands, is abundantly verified in the native fruits of the Mississippi Valley states as well; where the various wild berries, haws, plums, etc., are well known to the younger part of the population to be much sweeter and higher-flavored in certain (calcareous) localities than in others, besides being usually more abundant.
This is entirely in accord with the well-known fact that the application of lime checks the excessive wood and leaf growth resulting from excess of nitrogen as well as moisture; while on the other hand, the injurious effects of overdressing with lime or marl are known to be repressed by the use of stable manure, or by green-manuring. The repression of excessive wood growth by lime would seem to offer a simple explanation of the compact habit of growth on calcareous lands; and the extraordinary sweetness of fruits grown in the arid region as compared with the same in the humid, is fully in accord with the high lime-content of the arid lands.
Stunted Growth.—In practice it will be found in most cases that a stunted native growth is due not so much to lack of plant-food in the soil, as to unfavorable physical conditions. Among these, shallowness, and extreme heaviness of the soil are the most common causes. The “scab lands,” underlaid by impervious rock at a depth too slight for culture plants, as in many plateaus of the Pacific Northwest, and in rocky or mountainous regions generally, are cases in point. Strata of impervious clay often produce the same result; but in this case, should such clay be intrinsically capable of supporting plant growth, the land can often be made available for orchard purposes by blasting with dynamite (see chapter 10, p. 181).
The post oak (and black-jack) flats of the Mississippi Valley states are familiar examples of land whose dwarfed tree growth causes it to be avoided by settlers; similarly, a dwarfed growth of red elm (Ulmus rubra), hackberry and ash indicates in the flood plain of the Red river of Louisiana a heavy “waxy” red clay, or “gumbo” land, scarcely available for agricultural purposes.[190] The gray or white “cray-fishy” bottom and bench lands of the Southwestern States, so poor in lime, phosphates and humus as to be worthless under existing conditions, are characterized by an easily recognized scrubby growth of Water and Willow Oaks (Q. nigra, or aquatica, and phellos), with low, rounded tops; while the same trees, when well developed, indicate highly productive lands.
[190] Rep. of Geological Reconnaissance of Louisiana; New Orleans, 1873, p. 27.
Physical vs. Chemical Causes of Vegetative Features.—The extent to which the modifications of form alluded to above are referable to chemical and physical causes respectively, can be approached by the discussion of the presence or absence of certain trees from soils of extreme physical character, but otherwise normally constituted. As has been shown above, the black-jack and post oaks belong, as species, equally to the heaviest and lightest soils within the state of Mississippi; to the black and yellow “prairie” soils, as well as to the sandy ridges of the yellow-loam region; showing for these two species as such, an independence of physical conditions and an extraordinary adaptability, found in few other trees. They are frequently found either alone or associated with only a few other species of local adaptation, such as, in the prairie lands, the crab-apple, wild plum, and the juniper or red cedar. On the soils of intermediate or loam character, on the contrary, they are always associated with other oaks as well as with hickory, and in that association attain what may be considered their normal type or form.
From the fact that the dense, rounded top is formed by the black-jack oak both on the rich prairie lands and on the poor soils of the Flatwoods, it would seem that that form is the outcome of a physical cause, viz., the extreme “heavy-clay” character of both kinds of land; and we may note that exactly the reverse effect is observed in the form growing on the poor sandy ridges, as shown in fig’s 79 and 80. Yet it will also be noted that in the case of the post oak, the poor, heavy-clay soil of the Flatwoods produces an open, broom-shaped top, while the form assumed on the sandy ridges is substantially the same for both species. Care must therefore be exercised in drawing general conclusions as to the effects produced by either physical or chemical causes, alone, upon tree forms.
Lowland Tree Growth.—The variations occurring in the valleys or alluvial bottoms are less obvious to superficial observation, yet equally important and cogent to the close observer. In the properly alluvial lands, one dominant condition, that of adequate moisture supply, is almost always fulfilled, irrespective of soil quality. In addition to this, as stated in chapter 2 (see page 24), practically all the alluvial lands of the humid region may be considered as being of a more or less calcareous character, as compared with the adjacent uplands. These two important conditions dominate in a great measure the minor ones of variation in soil-texture. Yet where, as is largely the case in the southern part of the State of Mississippi, the amount of calcic carbonate is insufficient to overcome the sourness of the soil, the vegetative contrasts become extremely striking and characteristic, as explained above.
Contrast Between “First” and “Second” Bottoms.—A very striking phase of transition between the alluvial bottoms and the uplands proper in the Cotton States are the second bottoms or hammocks of the streams, whose soil and tree-growth in most cases differ markedly from those of the first bottom; and these being usually closely adjacent, often afford a very striking contrast to the latter. From some antecedent geological cause not fully understood, these hammocks, usually elevated from 4 to 10 feet above the present flood plain, have almost throughout soils of a fine sandy, pulverulent or silty nature, frequently in strong contrast to heavy clay soils in the first bottom.
They seem, moreover, to have been at some time subject to prolonged maceration under water, resulting in the reduction of the ferric oxid, and its accumulation in the lower portion of the deposit in the form of bog-ore spots or “black gravel.” Since such a process always results in the abstraction of phosphoric acid from the general mass of the soil, to be accumulated in the bog ore in an inert condition,[191] these hammock soils, usually whitish or gray in color, are almost throughout poor in phosphates as well as in lime; the latter having been definitively leached out. The resulting vegetation, as may be imagined, is widely different from that of the bottom proper, as well as, frequently, from that of the adjacent uplands; and though level and fair to see, these hammocks are usually unthrifty and last but a short time under exhaustive cultivation. Accordingly, their forest growth is prevalently that of the poorer class of uplands, viz., small-sized post and black-jack oaks, and in the low ground depauperated water oak, or less commonly willow oak, of the low, stunted type indicative of a soil of inferior productiveness. The luxuriant growth of the present alluvial bottom is often seen within a few feet of the unthrifty vegetation of these hammocks. It is usually only in the limestone regions, and in the lower course of the larger streams, that the hammocks or second bottoms are found to be of good fertility.
[191] See Chapter 2, p. 24.
The Tree Growth of the First Bottoms. The Cypress.—Among the trees occupying the low ground of the first bottom in the southern Mississippi states, the deciduous cypress (Taxodium distichum) deserves special mention as an example of extreme variation in form. In sloughs and swampy tracts, as is well known, the cypress grows with roots submerged throughout the season, excepting only the excrescences known as “knees,” which project above the water, probably performing some function in connection with the aeration of the root, which is essential to the root functions in all plants. The trunk rising from the water is supported by numerous projecting buttresses for from 8 to 15 feet above the water; higher up it becomes cylindrical for a height of from 40 to 70 feet, then divides up into a few widely spreading, thick, almost conical branches, whose twigs and foliage form an almost level surface to the head. This level-topped forest growth characterizes at once the submerged areas of the river and coast swamps.
But the cypress is by no means confined to the swamps and sloughs; it is also found occupying the better class of hammock lands, 12 or 15 feet above water level. In this case, however, the tree assumes a shape and growth so wholly different from that described above as to lead to a popular assertion of a difference of species. As a matter of fact, however, the cones of these upland cypresses, when dropping into the water below them, reproduce exactly the common swamp form. The extraordinary difference in the aspect of the tree under these different conditions is best seen in the subjoined diagram, showing the upland cypress to assume the form of the tall willow oak, with which it is sometimes locally associated.
The trees from which the annexed sketch is taken grew within thirty feet of each other, on Yellow creek, a small tributary of the Tennessee river, in Tishomingo county, Miss. The soil stratum is underlaid by a shaly limestone, and bears lime vegetation.
The fact that the deciduous cypress grows without difficulty on the moister class of lowlands in California, 12 or 15 feet above bottom water, is of interest in this connection. It then assumes the upland form shown in the figure above, although not growing quite as tall. The calcareous nature of these soils is probably an important factor in this apparently incongruous adaptation of a subtropical swamp tree to arid conditions. In its swamp form the cypress usually grows in rather shallow, heavy clay soil, into the dense subsoil of which the roots penetrate but little.
Other Lowland Trees.—The lowland hickories, like their brethren on the highlands, seem on the whole to prefer the lighter or loamy bottom soils to those of a heavier character. This is especially true of the Pecan. The latter, as well as the shell-bark hickory, is especially indicative of the highest class of bottom soils. The black walnut, while apparently also best suited in loamy soils, is also more or less found on heavy bottom lands, provided they are sufficiently calcareous; and the same is measurably true of the tulip or white-wood tree. The most frequent occupants of heavy bottom lands, however, are the black gum and sweet gum, so that “gum swamps” are usually found to be of that character.[192] But in the prairie region, where the bottom soils are very calcareous and heavy, as well as in corresponding soils of the “buckshot” lands of the great Mississippi Bottom, the chestnut-white (cow- or basket-) oak sometimes occupies such ground almost exclusively. Among the accompanying trees are especially the honey locust, the crab-apple, mulberry and sweet gum, as well as ash.
[192] Hence perhaps the vernacular name “gumbo” for heavy, adhesive clay soils in the north central states; which may also, however, be derived from a comparison with the “gummy” pods of the cultivated okra or gumbo plant.
General Forecasts of Soil Quality in Forest Lands.—While the oaks and pines mentioned as forming the bulk of the timber constitute in the cotton states the primà facié evidence, as it were, of the general character of the land, there are numerous other trees and plants which serve the discriminating land-seeker as a guide for the quality of the soils in different localities. While everywhere, well-developed black, red, Spanish and white oaks are considered as signs of a high quality of land, the tall, thin scarlet, the upland willow, and the barrens scrub oak are considered as indications detracting materially from the producing value wherever they prevail. The various hickories are throughout considered as indicating good land when mixed with the oaks, or by themselves; while the presence of walnut, linden and tulip tree will usually raise the estimate of uplands to the highest class. On the other hand, the occurrence of small black-gum trees and short-leaved pine, with low huckleberry, among the oaks of whatever kind, accompanied as they usually are by the disappearance of the black, white and Spanish oaks, will materially depress the land-values.
The appearance of well-formed oaks, as well as of hickory, is therefore at once welcomed as an evidence of soil improvement, while that of low huckleberry bushes and small black gums indicates the reverse. An increase in the thickness and retentiveness of the soil stratum is also usually indicated by the occurrence of short-leaved pine in the long-leaf-pine areas.
The black, red, white, and Spanish oaks belong altogether to soils of medium physical constitution, only their size upon such lands depending upon the relative richness in plant-food; but without such changes producing any notable variation in their form. Clearly then, these species are intolerant of extreme physical conditions, and are practically restricted to soils of “loamy” character and easy cultivation.
Chapter XXV
RECOGNITION OF THE CHARACTER OF SOILS FROM THEIR NATIVE VEGETATION. UNITED STATES AT LARGE. EUROPE.
The application of the above data outside of Mississippi can mostly be verified only in a fragmentary way from such data as are casually given in the reports of State Surveys, as well as from such observations as the writer has been able to make personally elsewhere. In the latter category the most copious refer to the states of Alabama, Louisiana and Illinois.
ALABAMA.—The observations of Prof. Eugene A. Smith, and those of Dr. Chas. Mohr, are especially valuable and cogent as to the close correspondence of the soil and vegetative phenomena with those observed in Mississippi.[193] They are faithfully reproduced on the corresponding geological areas, including also the Flatwoods. Northwest of Mobile, on the Mississippi line, the long-leaf-pine forest is interspersed with more or less continuous areas bearing a fine oak growth, with hickories and other trees indicating a calcareous soil. This feature is most extensively developed in Alabama in what is known as the “lime-sink region,” on the borders of which the vegetative transition in passing from the non-calcareous sandy pine land, can be observed in the most striking manner and with frequent alternations. Northward of the long-leaf-pine belt, the tertiary and cretaceous areas show in Alabama the same features as in Mississippi, viz., black calcareous prairies alternating with ridge lands, among which in the cretaceous area the Pontotoc ridge is represented by a series of isolated knobs, popularly known as Chunnenugga ridge, closely resembling the former in its soils and vegetative character.
[193] See Plant Life of Alabama, by Charles Mohr, Vol. VI. Contr. U. S. Nat. Herb., U. S. Dep’t Agr.; Alabama Ed. of Same, Ala. Geol. Survey, 1901.
In northern Alabama, according to Dr. Smith, on the various stages of the Carboniferous formation, ranging from a sandy or conglomerate character to that of limestones of various degrees of purity, soils contrast strikingly with each other, agreeing closely with those seen in the neighboring part of Mississippi. Here, moreover, the contrast between the natural vegetative character as well as cultural value of the lands derived from the magnesian limestones (the “barrens”) contrasts strikingly with those originating in the purer limestones, on which the blue grass is at home.
LOUISIANA.—As to Louisiana, whose geological formations correspond closely to those of Mississippi, it may be said in general that the vegetative phenomena coincide completely with those observed in Mississippi. The “white-lime country” of northeastern Mississippi is represented in Louisiana only by patches occurring here and there on a line laid from Lake Bistineau to the coast at Petite Anse Island. But the chief characteristics of the calcareous area, among them especially that of the occurrence of red cedar and clumps of crab-apple, persistently reappear. The “Central Prairie Region” of Louisiana is quite narrow, but on it there reappear precisely the same characteristics described in connection with that area in Mississippi. In the long-leaf-pine region of Louisiana there occur, as in Mississippi, some isolated patches of a calcareous character, the largest of which is on the Bayou Anacoco in Vernon Parish, near the western border of the State. As we emerge from the sandy lands of the long-leaf pine area to that underlaid by the calcareous formation, we find, first, a change to oak and short-leaved pine, then the oak forest alone; finally, on a level black prairie of considerable extent, the post and black-jack oak in their thick-set form, clumps of crab-apple, red haw and honey locust, here and there a red cedar; exactly as has already been described in connection with the prairie lands of Mississippi. To southward of the long-leaf-pine area lies a broad belt of level, generally treeless, sandy prairie, in part dotted with groves of timber, but otherwise with nearly the same peculiar, small-seeded herbaceous vegetation observed in the corresponding portion of Mississippi. But in Louisiana there intervenes between these gray sour lands and the shell hammocks of the immediate sea-coast with their groves of live-oak, a belt of black calcareous prairie, increasing in width and clayeyness towards the West, and acquiring considerable extension in the corresponding portion of Texas. On these prairies we again find the calciphile vegetation, including the honey locust, clumps of crab-apple and red haw, etc., but not usually any oak growth, except (near the sea-coast) the live-oak. In the hilly country of northern Louisiana there is reproduced substantially the vegetative character of the “short-leaf pine and oak” uplands of Mississippi (see map on p. 490, chapter 24), save in that, owing to the occasional outcropping of the calcareous materials of the Tertiary, small prairies with black soil are spotted about here and there. Bordering the Mississippi Bottom there are a series of oak-upland ridges with a brown loam soil corresponding to the fertile area in northwestern Mississippi, with small patches of the “Cane hills” loess soils, bearing a corresponding tree growth.[194]
[194] See “Final Report of a Geological Reconnoisssance of Louisiana,” published by the New Orleans Academy of Science in 1871.
In Western Tennessee the vegetative zones so distinctly shown in the adjacent portion of Mississippi are not so strikingly outlined, but so far as they do exist, the phenomena observed accord exactly with those heretofore described. The same holds true of Western Kentucky, as is well set forth and graphically described in the reports of the geological surveys of that state by Dr. David Dale Owen, and later by Dr. R. H. Loughridge.
North Central States.—North of the Ohio River the materials of the geological formations are not nearly as much varied as they are south of the same; consequently the vegetative features are also much more uniform. It must be remembered that from the Alleghenies nearly to the Mississippi, the states of Ohio, Southern Michigan, Indiana and Illinois are largely covered by drift deposits overlying the older formations, except that along the Ohio and Mississippi rivers lies the calcareous loam of the Loess or Bluff formation.
Within the states mentioned, however, not only are the older underlying formations very generally calcareous, but calcareous sand and gravel form a large proportion of the drift deposits, which in most cases overlie the rocks. Hence we find from the Alleghenies to the Mississippi a predominance of the oak forests which characterizes calcareous soils, as in the better class of uplands in Mississippi and Tennessee; interrupted only here and there by sandy belts or ridges bearing inferior growth, among which, again, the black-jack and post oaks, with short-leaved pine, are conspicuous. But in a large portion of Illinois, as well as in Western Indiana, the oak forest is interrupted by more or less continuous belts, and sometimes by a wide expanse, of black prairie, generally treeless or bearing only clumps of crab-apple and haw, and underlaid more or less directly by the carboniferous limestones, whose disintegration has materially contributed to the black prairie soils; which are noted for their high and long-continued productiveness. The lower ground is characterized, besides clumps of crab-apple and red haw, by the frequent occurrence of the honey locust, the lead plant (Amorpha fruticosa), the button-bush (Cephalanthus occidentalis), and among herbs by the polar plant (Silphium laciniatum), the prairie burdock (S. terebinthinaceum), the swamp rose-mallow (Hibiscus moscheutos), the sneezewort (Helenium autumnale), the wild indigo (Baptisia tinctoria and leucophcæa).
The black-jack and post oak are not nearly as frequently found on the prairies of Illinois as on those of Mississippi and Alabama; but where they occur they assume a similar habit, including the occurrence of the dwarfed, apple-tree-shaped form on the low ridges with heavy yellow clay soil, that sometimes intersect the prairies. The post oak, moreover, in a form quite similar to that described as occurring on the Flatwoods of Mississippi, forms the timber of the “post oak flats” occasionally found between the low ridges bordering the streams, or along the edges of the prairies. The herbaceous vegetation of these post oak flats distinctly characterizes them as being poor in lime. In the loamy uplands, where the calcareous ingredient is more abundant, the open-headed form of the black-jack and post oak are also found, interspersed with a luxuriant growth of black, red and white oak, with more or less of hickory, which here assume a magnificent development, much superior to that seen south of the Ohio. These yellow-loam uplands correspond very closely in their soil-composition and agricultural character to the brown-loam area of Mississippi and Tennessee, which lies inland from the Loess belt. Where these uplands approach the prairie or the outcrops of a limestone formation, there is usually added to the oak growth the linden, the wild cherry and the ash; the latter two also usually appear in the bottoms of the streams and on the slopes adjacent, together with the walnut and butternut, and in the lowest ground the sycamore.
The tree growth of the Loess belt bordering the Ohio and Mississippi, so far as climatic differences permit, agrees almost precisely with that described in the corresponding portions of Mississippi and Tennessee. The change from the oak and hickory growth covering the yellow-loam uplands toward the more calcareous area is evidenced by the appearance of large sturdy trees of sassafras, together with the linden and sugar maple. Descending from the “bluff” toward the rich bottom-prairie with its black, heavy soil, we at once encounter the familiar indices of the more highly calcareous land, viz., the honey locust, clumps of crab-apple and red haw, with hackberry, Kentucky coffee tree and mulberry on the lower ground. In late summer and during autumn, a tall growth of the iron weed (Vernonia), several Eupatoriums (E. perfoliatum and purpureum, the white and the purple boneset) and of the blue-spiked Verbena are very characteristic, as are also several species of Cassia (Carolina coffee, etc.,) and the swamp rose-mallow.
Upland and Lowland Vegetation in the Arid and Humid Regions.—In the humid countries there is commonly a marked difference between the vegetation of the uplands and lowlands, arising not merely from the difference in the moisture supply, but evidently of a specific nature. When we discuss the characteristic plants in detail, it becomes obvious that it is lime vegetation that, in most cases, forms the characteristic differences between upland and lowland forest growth; a natural consequence of the leaching-down of the lime from the higher land to the lower levels. By way of counter-proof we find that when the uplands themselves are of a calcareous nature, a part at least of the lowland flora ascends into them. As prominent examples may be mentioned the Tulip tree (Liriodendron), black walnut, ash, Kentucky coffee tree, Hercules’ club, etc., which are lowland trees over the greater part of their area of occurrence; but in the loess or Cane hills bordering the Mississippi and its larger tributaries, as well as in the limestone regions of the southwestern and western states, are conspicuous in the uplands as well. The tall southern cane (Arundinaria macrosperma), usually considered a plant of the low river bottoms, originally covered the loess or “Cane hills” of the lower Mississippi, with their highly calcareous soils. The same is true of many other trees and shrubs characterizing limy lands. Of course there are some whose habitat is dependent upon the concurrent presence of both lime and moisture, such as the sycamore, cottonwood, hackberry, pawpaw, etc., which are naturally found only in stream bottoms or on low hammocks.
In the arid region, on the contrary, the main difference in upland and lowland vegetation is (outside of mountain influences) entirely referable to moisture-conditions; the proof being that so soon as the uplands are irrigated the lowland flora takes possession. Both uplands and lowlands being abundantly calcareous, there then is no cause for any material differences. This substantial uniformity of upland and lowland plant growth is particularly striking in the comparatively restricted floras of Eastern Oregon and Washington, and in Montana, where the more luxuriant growth of the valleys is almost the only contrast seen when their vegetation is compared with that of the uplands adjacent.
Forms of Deciduous Trees in the Arid Regions.—Since, as shown above, the soils of the arid regions are almost throughout calcareous, we should expect that the forms of the native trees would in general conform to the rule given above. As regards the deciduous trees this is very generally true: We rarely see on the Pacific slope, south of Oregon, anything to compare with the tall oaks of the Atlantic forests. The native oaks are as a rule of low, spreading growth, with stout, short trunks; and as they rarely form dense forests, the timbered areas have an orchard-like appearance, characteristic of the landscapes of the arid region, from the Mezquit Plains of Texas to Eastern Oregon and Washington. Only where a very abundant supply of moisture prevails do we find occasional exceptions. The trees of the humid region when transplanted to California have a perverse tendency to branch low, so that only the most persistent trimming-up will induce them to form trunks at all like those found in their native climes. In some cases no amount of trimming will result in the formation of anything more than bushes.
It may be objected that the arid climate as such, and not the calcareous nature of the soil, is the cause of this tendency. It is unquestionable that this low-branching habit is a distinct advantage to the plants, whose trunks would otherwise be frequently scorched by the hot summer sun; as happens when Eastern settlers try to grow “standard” fruit trees, with the result that a “sore,” or sunburnt streak is formed on the southwest side of the exposed trunk. All orchard trees should therefore be pruned “vase-shape” in arid climates, partly for this, partly for other reasons. But this cannot explain the fact that seedlings from eastern acorns act precisely as do acclimated trees; so that it is not a case of the survival of the fittest to endure arid conditions.
Tall Growths of Conifers. Moreover, while the rule holds good with almost all deciduous trees, it is not applicable to the Conifers; which in the case of the Sequoias (redwoods and “big-trees”), sugar pine and others, exemplify some of the tallest growths known in the world. The Eastern Cedar or Juniper grows tall only on sufficiently calcareous soils, and in the Mississippi Valley states at least, wherever it occurs is an unfailing indication of calcareous lands. The extended occurrence of the spruce on the Allegheny Ranges, where limestone formations prevail so largely, seems to indicate a similar preference for calcareous lands. And this is certainly true of the black locust, which reaches its extreme southern range in the cretaceous hills of Northeastern Mississippi, showing the stout, stocky form it also assumes when planted in the calcareous black-prairie lands of Illinois.
Herbaceous Plants as Soil Indicators. While herbaceous plants are not as generally considered by land-seekers in judging of soil fertility and character, it goes without saying that very many are quite as characteristic as the tree vegetation, especially when deep-rooting, so as not to indicate merely the character of a few inches of surface soil.
In the Middle West of the United States especially, a large number of the Compositæ serve as marks of high productive capacity. This is particularly true of the larger species of the sunflower tribe, among which Helianthus grosse-serratus and doronicoides are perhaps the most generally notable; while farther west, beginning with Kansas, the “Sunflower State,” and its northern neighbor, H. annuus, whether native or introduced, becomes conspicuous also. The Silphiums (compass sunflowers) have nearly the same significance, S. laciniatum and perfoliatum being prominent on the prairies of Illinois and Indiana; but in land under cultivation they are mostly replaced by a luxuriant growth of the Ragweed, Ambrosia trifida. Various species of Bidens (beggar ticks), notably the B. aristata and cernua, accompany the true sunflowers in the lower grounds of these regions, as do also Heliopsis laevis, Coreopsis triperis and Rudbeckia (Obeliscaria) pinnata. Rudbeckia hirta and purpurea, though also occurring on rich soils, are not characteristic of them. The larger species of golden rods (Solidago), notably S. canadensis, rigida and speciosa (not ordinarily distinguished by farmers) share substantially the distribution of the large sunflowers mentioned above. Of the Asters, only A. novæ-angliæ serves as a reliable guide to high-class lands in the Middle West,[195] but a very copious growth of asters and solidago of various species is always a welcome indication of land quality, and indicates soils of good lime content, if not absolutely calcareous.
[195] In view of its specific designation and the reputed poverty of New England soils, this is rather unexpected.
Leguminous Plants.—It is generally understood that most leguminous plants, and among them especially the clovers, indicate rich, or rather, calcareous lands. The very large proportion of lime contained in the ash of legumes at once creates this presumption, which is fully confirmed by experience so far as our ordinary culture plants of that relationship are concerned. The favoring effect of lime on the development of bacteria, so essential to the full development of cultivated legumes, has already been referred to. The favoring effect of gypsum sown even in small amounts with clover and other legumes, may probably be referable to the known action of that salt in promoting nitrification, which in the first stages of leguminous growth is so highly favorable to a vigorous and early start of the crop, and to a more copious production of the nitrogen-assimilating nodules. The quick change noted in meadows and pastures of languishing production so soon as moderately limed, by the appearance of clover among the herbage, at once reminds us that the Rhizobia do not flourish in acid lands. The great prevalence of leguminous plants of all kinds in the arid region—clovers (not fewer than twenty-three species in California alone), Lupins, Astragalus and related genera, at once remind us of the universal prevalence of calcareous soils in these regions, as shown above. Mutatis mutandis, we find precisely the same general facts in the arid regions of the other continents.
Nevertheless, it must be kept in mind that not all plants of the leguminous order are positively “calciphile.” Within the United States, it is especially the genera Desmodium (Meibomia) and Lespedeza, which are very numerously represented in the long-leaf pine region of Mississippi, where the soils are so poor in lime. Whether under these conditions these plants develop the rhizobian nodules, has not, so far as the writer is aware, been definitely observed. Certain it is that quite a number of these plants occur on both calcareous and non-calcareous soils, and on the latter assume a much more vigorous development than in the pine woods. But it is evident that they, with a few others (e. g. Galactia mollis, Cassia chamæcrista and nictitans) are more or less indifferent to the lime-content of soils, and cannot therefore be relied upon in judging the quality of lands. In Mississippi and northern Alabama, the Tephrosia virginica (“devil’s shoestring”), associated with chestnut and short-leaved pine, is characteristic of the poorest non-calcareous lands, and bears seeds but very scantily. It disappears so soon as calcareous lands are approached, together with the chestnut tree.
EUROPEAN OBSERVATIONS AND VIEWS ON PLANT DISTRIBUTION AND ITS CONTROLLING CAUSES.
The writer has thus far presented and discussed mainly his own observations made in the United States, without reference to the previous and contemporaneous work on the same subject in Europe. There arose certain discrepancies which could not well be explained without a previous full consideration of American conditions.
As is well known, for nearly twenty years the accepted theory in Europe was that of Thurman,[196] which attributes the distribution of the native floras entirely to physical conditions; thus anticipating by more than half a century the corresponding hypothesis lately brought forward by the U. S. Bureau of Soils. Thurmann classes plants simply as hydrophile and xerophile, thus differing from most of our modern ecologists merely in omitting the transition phase of “mesophytes,” which now serves as a convenient pigeon-hole for an indefinite variety of plants.
[196] Essai de Phytostatique appliquée à la chaine du Jura et aux contrées voisines. 2 vols. 8vo. Berne, 1849.
While gradually many were led by their observations to doubt the correctness of Thurmann’s exclusive physical theory, Fliche and Grandeau[197] were apparently the first to impair by their investigations the confidence in the accepted view. They investigated exhaustively the conditions under which the maritime pine and the chestnut tree, both antagonistic to lime, would flourish, and proved that the presence of any considerable amount of lime in the land would cause them to languish or die, although the physical conditions so far as ascertainable were exactly alike. It is interesting to note what were the lime-percentages which caused these differences; viz., for the “non-calcareous” soil and subsoil, respectively, .35 and .20%; for the calcareous land, 3.25 and 24.04%, the latter evidently being decidedly “marly.” The composition of the ash of these trees is very instructive, and is therefore given in full. Alongside of the ash of the maritime pine on the two soils is given that of the Corsican pine, a lime-loving tree.
COMPOSITION OF PINE ASHES ON CALCAREOUS AND NON-CALCAREOUS LANDS. -----------------+-------------------------------+-------------- | MARITIME PINE, | CORSICAN PINE, | PINUS PINASTER. |PINUS LARICIO. -----------------+-----------------+-------------+-------------- |On non-calcareous|On calcareous|On calcareous | soil. | soil. | soil. | | | Potash | 16.04 | 4.95 | 13.56 Soda | 1.91 | 2.52 | 2.24 Lime | 40.20 | 56.15 | 49.13 Magnesia | 20.09 | 18.80 | 13.49 Ferric Oxid | 3.83 | 2.07 | 3.29 Silica | 9.18 | 6.42 | 7.14 Phosphoric acid | 9.00 | 9.14 | 11.33 -----------------+-----------------+-------------+-------------- Total | 100.25 | 100.04 | 100.18 -----------------+-----------------+-------------+-------------- Ash per cent. | 1.32 | 1.54 | 2.45 -----------------+-----------------+-------------+--------------
[197] Annales de Chimie et de Physique, 4me série, tome 29; ibid. 5me série, Tome 2. Also, ibid, tome 18, 1879.
It is very interesting to note in these analyses the inverse ratio in the absorption of potash and lime by the maritime pine, which seems to be unable to defend itself against excessive absorption of lime and thus experiences a dearth of potash which naturally interferes with the formation of starch and chlorophyl; hence probably induces the chlorosis so well known to occur on excessively calcareous soils. The lime-loving Corsican pine takes up a larger total amount of ash and more phosphoric acid, and nearly three times as much potash, but considerably less lime than did the maritime pine on the same calcareous soil.
The corresponding analyses made by Fliche and Grandeau, of the leaves and wood of chestnut grown on the same two kinds of soils, gave in general the same results; and they add that the smaller content of iron absorbed by the calcifuge trees when grown on calcareous soil point also to a deleterious influence upon the normal formation of chlorophyl.
Following Fliche and Grandeau, Bonnier[198] made corroborative tests by sowing seeds of the same plants, both calciphile and calcifuge, upon the two kinds of soils, and noting the differences in their mode of growth and internal structure.
[198] Bull. de la Société Botanique de France, tome 26, 1879.
Calciphile, Calcifuge and Silicophile plants.
The subject has been somewhat exhaustively discussed by Contejean[199] who enumerates and has classified under the three general heads of calciphile, calcifuge and indifferent, over 1700 species of European plants. Unfortunately he had but few soil analyses at his disposal, and was inclined to consider as non-calcareous, most soils that gave no effervescence with acids. But notwithstanding this disadvantage so far as his contention of the efficacy of chemical soil-composition, and especially of lime is concerned, he disproves very effectually the physical theory of Thurmann, by numerous examples from France and elsewhere in Europe; and also disposes very definitely of the claim that there is a special class of “silicophile” plants. He concludes that silica (and sand) is merely a neutral and inert medium which offers refuge to the plants “expelled” by lime; and that clay similarly exerts no chemical but only a purely physical action. That potash, phosphoric acid and nitrogen, while most essential as plant-foods, exert otherwise little if any effect on general plant distribution. He alludes similarly to magnesia; and his final conclusion is that “chemical are in general more potent than physical influences,” and that the most widely active influences are carbonate of lime and chlorid of sodium. He does not, of course, deny the potent influence of moisture upon plant distribution.
[199] Geographie botanique. Influence du terrain sur la vegetation. Baillère et Fils, Paris, 1881, 143 pp.
Since these publications were made, many observers have investigated the subject, and the broad distinction between lime-loving or calciphile and lime-repelled or calcifuge plants has been very generally recognized and discussed: but the cause of this discrimination by plants is still more or less the subject of controversy. Some still claim that the calcifuge plants (such as the chestnut, the huckleberries and whortle-berries, the heather and many other Ericaceæ, most sedges, etc.) are repelled by calcareous lands because they need a large supply of silica, which they suppose cannot well be assimilated in presence of much lime; hence they also designate the calcifuge plants as “silicophile”; while others attribute the preference of calciphile plants to the physical effects produced upon the soil by lime, as outlined above (chapter 20, page 379).
The contention that the presence of much lime in soils renders silica insoluble and hence unassimilable by plants, is at once negatived by the fact that waters exceptionally rich in silica, partly simply dissolved by carbonic acid, partly in the form of water-soluble alkali-silicates, are very abundantly found in the arid region. This is especially the case in California, where moreover a number of species of very rough-surfaced horsetail rushes and grasses prove the ready absorption of silica when wanted, even in strongly calcareous soils. But the question is whether the supposed class of silicophile plants is a reality or merely a theoretical fiction, based upon the habit of speaking of “siliceous” soils as a class apart from other and especially heavier or clay soils. As a matter of fact, the siliceous soils usually so called are simply those poor in clay and lime—in other words, “light” lands, the outcome of the weathering of quartzose rocks into sandy soils, which in the humid region are always poor in lime because thoroughly leached. In the arid region, on the contrary, sandy lands are quite commonly just as calcareous as the heavier soils, and show no “silicophile” flora.
According to the writer’s observations and views, it being obvious that some plants are practically indifferent to the presence or absence of lime in the soil except in so far as it influences favorably the physical conditions, moisture must always stand first as the condition of maximum crop production, and as a conditio sine qua non of the best development of plants on all kinds of soils; its best measure being a matter of special adaptation to each species. But this being understood, he agrees with Contejean as to the commanding influence of lime in determining the adaptation of soils to plants, both cultivated and wild. At the same time, it is obvious that the absence of the opportunity to observe really native vegetation, adapted to the soils through ages, has created for European observers difficulties which are readily solved where original native floras are available.
Schimper[200] says pointedly that observations prove that the differences between the location of plants on calcareous and siliceous soils are not constant, but vary from province to province; that e. g., the list of indifferent (bodensteter) plants for the Alps do not hold good in the Dauphiné, still less between the Carpathians and Skandinavia. According to Wahlenberg the following species are calciphile in the Carpathians, and according to Christ indifferent in Switzerland: Dryas octopetala, Saxifraga oppositifolia, most of the leguminous species, Gentiana nivalis, G. tenella, G. verna, Erica carnea, Chamæorchis alpina, Carex capillaris. Geum reptans is reported by Bonnier to be exclusively calciphile on Mont Blanc, exclusively silicophile in the Dauphiné; indifferent in Switzerland. A great number of similar contradictions are reported by others as well, and the entire subject thus becomes rather vague; so that Schimper and others suggest that climatic conditions may in part be responsible for these discrepancies.
[200] Pflanzengeographie, p. 111 & ff.
In all, or nearly all these cases, it is tacitly assumed that the underlying geological formation has essentially been the source of the soil, and that its character is determined accordingly. But this assumption is wholly arbitrary unless confirmed by actual direct examination. A soil-formation overlying limestone on the slopes of a range may be wholly derived from non-calcareous formations lying at a higher elevation, or may have been leached of its original lime-content by abundant rains. The feldspars constituting rocks designated as granite, may or may not be partially or wholly of the soda-lime instead of the potash series; the mica may or may not be partially replaced by hornblende, in which cases the soil would be calcareous to the extent of determining the character of the flora as calcifuge or calciphile, without its being at all evident in the physical character of the soil, which would still be “granitic” or “siliceous.” Such observations in order to be critically decisive, clearly require that the observer should be, not merely a systematic botanist, nor a mere geologist or chemist, but all these combined. There is good reason to believe that most or all of these supposed contradictions would disappear before a critical physical and chemical examination of both the soils and the rocks from which they are supposed to have been derived. Contejean himself, in placing so many of his long catalogue of plants into the doubtful groups, suggests many cases in which the above considerations may explain the apparent discrepancies.
What is a calcareous soil? The definition adopted for this volume has been given in a previous chapter (chapter 19, page 367); viz, that a soil must be considered calcareous so soon as it naturally supports a calciphile flora—the “lime vegetation” so often referred to above and named in detail. Upon this basis it has been seen that some (sandy) soils containing only a little over one-tenth of one per cent of lime show all the characters and advantages of calcareous soils; while in the case of heavy clay soils, as has been shown, the lime-percentage must rise to over one-half per cent to produce native lime growth. While in the United States observations of the contrasts between calciphile and calcifuge floras are easily made in the field, and the facts must attract the attention of any fairly qualified observer, in Europe they would have to be made the subject of special cultural investigation based upon soil analysis; a procedure not yet fully accredited abroad, any more than in the United States. In a general way it has however been recognized by Maercker, as shown at the end of the preceding chapter. How far this estimate was based upon American precedents, can now be only conjectured. Certain it is that the European definition of calcareous soils remains to the present day a wholly different one from that stated above; and from this have arisen the greater part of the doubts and differences of opinions among European botanists as to the classification of plants in relation to calcareous soils. Two per cent of lime (equivalent to nearly double the amount of carbonate) is the prevailing European postulate for a calcareous soil. Some go so far as to postulate effervescence with acids, requiring about 5% of the carbonate.
Predominance of Calcareous Formations in Europe.—It is not generally recognized even among geologists how abnormally predominant are limestone formations in Europe. In all works on European agriculture we find the “lime sand” mentioned as a normal ingredient of soils, specially provided for (or against) in the operations of soil examination. Its presence is the rule, its absence the exception. Soils as poor in lime as are those of the long-leaf and short-leaf pine regions of the United States, are there very exceptional and (like the “Haideböden” of northern Germany) have long remained almost uncultivated. Calcareous soils being the rule in the regions of intense culture, the ideas of both agriculturists and agricultural chemists have in Europe, in the main, been based upon them as normal soils; so that instead of comparing calcareous, and non-calcareous soils properly speaking—i. e., such as would not bear native lime-vegetation—the majority of comparisons has actually been made between soils which, in the American sense, were all or chiefly within the calcareous class. It is characteristic of this state of things that the injuriousness of an excess of lime is among the foremost themes of European (especially French and English) agricultural writers, as against the beneficent effects prominently assigned to lime in America. No such popular saying as that “a lime country is a rich country” exists in Europe; on the contrary, we constantly hear, and see in books, the mention of “poor chalk lands,” and in France especially the deleterious effects of excess of lime upon crops is the theme of remark. Excess of lime in their marly lands has been the despair of French vintners, and Viala was specially sent to America to find some vine to serve as a grafting stock which would resist the tendency to chlorosis which renders many of the American phylloxera-resistant vines useless to the viticulturists of France. Viala did not find such grapevines until he reached the cretaceous (chalk) area of Texas, where the native vines had long ago adapted themselves to marly soils; and these vines have solved the problem for French viticulture.
And England, France, Belgium and most of western Europe are rich countries, largely owing to their abundant limestone formations; and it may be questioned whether, had this been otherwise, Europe would so long have remained the center of civilization; for starving populations are not a good substratum for high mental culture and progress. It may equally be asked whether the invariably calcareous character of arid soils, as heretofore shown, has not, together with their general high quality, been largely a determining factor in the location and persistence of so many ancient civilizations in arid lands; as outlined in chapter 21, page 417. In this connection, the proper distinction between calcareous and non-calcareous soils passes from the domain of natural science to that of the history of human civilization.