UNIVERSITY OF CALIFORNIA AGRICULTURAL EXPERIMENT STATION. BERKELEY, CAL. E. W. HILGARD, Director. BULLETIN No. 108. THE DISTRIBUTION OF THE SALTS IN ALKALI SOILS. AUGUST, 1895. THE DISTRIBUTION OF THE SALTS IN ALKALI SOILS. By E. W. Hilgard and R. H. Loughridge. As time progresses the importance of the alkali question, i. e., of dealing successfully with the cultivation of lands more or less impreg- nated with soluble mineral salts, becomes more and more obvious. It is to be greatly regretted that the frequent mistaken efforts of land- owners to suppress, or at least to ignore, this matter for fear of injuring the selling value of their lands, interpose additional difficulties in deal- ing with an intrinsically sufficiently difficult problem. In view of this circumstance, we bear patiently the disappointment we have undergone in finding that, unexpectedly, one of our geographically most important culture experiment stations is almost wholly located upon ground sub- ject to the difficulties inherent in the cultivation of alkali land; since we are thus enabled to study the problem independently of any private interests. The culture experiment station near the town of Tulare, originally intended to represent the upper San Joaquin Valley at large, has thus, instead, become the station for the study of the alkali problem in all its phases, from the mildest to the worst. Until this problem is solved, no certain conclusions for the region at large can be drawn from the cultural results observed there; since we now know that all the vegeta- tion on the Station grounds is under more or less stress from the alkali in the soil. If, however, we shall be successful in overcoming this influence, as we hope to be, the Station will have rendered, not only to the San Joaquin Valley and the State at large, but to the entire region west of the Rocky Mountains, a most important service. NATURAL CONDITION OF THE LAND. For an understanding of the situation, it may be necessary to re-state here, that in their natural condition the lands of the Station, and for several miles around, as in hundreds of localities elsewhere in the val- ley and the State, show only occasional alkali spots; while outside of these spots, during the spring months, the country is covered with a luxuriant growth of native (largely annual) herbaceous plants, many being showy flowers and affording a most attractive sight; also proving beyond question the great inherent fertility of the land. As the season advances, from April to June, these plants go to seed or dry up, leaving the land more or less bare, or with only a sparse growth of hardy, drought-resisting, partially perennial plants. There is not, in ordinary seasons, any perceptible increase or decrease in the area of the inter- spersed alkali spots. When such land is put under cultivation without irrigation it will in years of unusual moisture bring very heavy crops of grain, which easily make up for at least one other season of almost total failure, when the rainfall is light or unfavorably distributed. It is this " fight- ing chance" of a highly remunerative crop that has in so many cases induced the investment of entire fortunes in such ventures, frequently with a total loss, and financial ruin as the result; a kind of agricultural gambling, little better in itself, and with as many chances against suc- cess, as that at the faro table, but now happily almost a thing of the past. BEHAVIOR UNDER IRRIGATION. With the advent of the irrigation ditch, the heavy grain crop becomes for a few years a matter of certainty. Then there is a gradual change for the worse. First it is noticed that the alkali spots increase their area outward, often merging neighboring small spots into one large one. Then new ones begin to appear, at first "no larger than a man's hand," but enlarging each year, and finally often so cutting up and reducing the producing area, that the land is abandoned in disgust. The "rise of the alkali" thus brought about by irrigation was very generally at first attributed (and sometimes justly) to the saline char- acter of the irrigation water used. But as in time it became apparent that even the purest waters, such as those of Kings and Kaweah Rivers, would produce the same result, the conclusion that the alkali salts are simply brought up by evaporation from the soil itself, forced itself upon the most superficial observers. THE QUESTION TO BE SOLVED. Then arose the question, " How much of these salts does the soil con- tain, or where do they come from?" If it could be shown that trie soil, subsoil, and substrata were equally impregnated with alkali, and would continue to supply indefinite amounts thereof, the reclamation of such lands for permanent cultivation would be almost hopeless. We at first approached the problem by the examination of " bottom waters" in cases where the latter had risen from a considerable depth in consequence of a filling-up from leaky ditches. It was found that in the vast majority of cases, such water contained relatively small amounts of alkali salts only; not more than many waters successfully used for irrigation elsewhere. It thus became evident that the main mass of these salts exists in the soil and subsoil within a short distance of the surface. The chemical examination of the "alkali" moreover showed that it consists, as a rule, of such compounds as are known to be formed in all soils in consequence of weathering; and that it contains all the ingre- dients useful, as well as those useless, to plant growth; substances which, in rainy countries, are currently leached out and carried into the coun- try drainage and finally into the ocean, but which in regions of scanty rainfall remain in the soil mass. We are thus led to the vitally important conclusion that the amount of the salts in these lands is but limited; and that if once removed, or rendered innocuous to crops in some other way, it will take thousands of years in the future, as in the past, before another such accumulation can occur from the very gradual weathering of the soil mass. In view of the extraordinary intrinsic and permanent fertility of alkali lands when once reclaimed, it has seemed desirable to study in detail the manner of the distribution of the soluble salts, as well as their — 5 — kind, at different depths in the soil and at different seasons ; so as to gain an insight into their migrations and transformations, and thus to determine the best and cheapest methods of dealing with them. The problem is a very complex one and involves a great deal of labor, hence cannot be solved in one or a few seasons, because of the great diversit} r of soil conditions in different localities. The investigation has already, however, yielded such striking and practically important results that it seems best to bring them to public notice at once. EXAMINATION OF SOIL PROFILES AND REPRESENTATION OF RESULTS. The obvious mode of determining the points in question was to sam- ple and examine the soil and subsoil at regular intervals of depth, in spots representing the land in its natural (unirrigated) condition on the one hand, and in the irrigated and cultivated on the other; tracing the effects of the latter conditions so definitely as to be enabled to con- trol, and repress them where desirable, at the proper times and by suitable means. For more ready understanding the results thus obtained are platted so as to show by means of curves, or lines drawn from point to point of actual determination, the increase and decrease of the total soluble alkali, as well as of the several salts composing it. As will be seen on the face of the plates below, the samples were taken (by means of a post-hole auger) so that each represented a vertical column of three inches of soil; continuing thus to the depth of two to four feet. Each of these samples was then leached of its salts, and every leaching analyzed separately. It was at first attempted to leach only the average of each foot, but this proved quite unsatisfactory. In the diagrams the depths are shown by horizontal lines at inter- vals of three inches, as marked on the margin to the left; while the unbroken vertical lines represent differences of either two or four hun- dredths of one per cent in the saline contents of the soil layers, as marked at the top of the diagram; increasing from left to right. Inasmuch as each sample represented the average of three inches of soil in vertical depth, in drawing the connecting lines or curves the result of the analysis is assumed to represent the middle portion of each three inches. Hence, the changes of direction always appear as occur- ring in the middle, vertically, of a three-inch space. The area embraced between each curve and the vertical line to the extreme left represents, of course, the aggregate amount of each ingredient enumerated, viz.: Common salt, Glauber's salt, and sal soda as the chief ones, with Chile saltpeter (nitrate of soda), also mentioned on account of its fertilizing value, where present in notable amounts. The potash compounds, usually constituting from 3 to 7 per cent of the salts, are not shown separately, being included in the "Alkali Sulphate" curve. The predominance of carbonate of soda seen in these diagrams shows at once that the Tulare alkali is very " black," so that the use of gyp- sum to change the carbonate into sulphate is the first thing needful in attempting any reclamation or preventive measures. But aside from this, the diagrams suggest, very instructively, the explanation of many points not well understood heretofore. — 6 — EFFECT OF THE RAINFALL. It is well known to residents that in Tulare and northern Kern Counties the greatest depth to which the soil is wetted by the winter rains rarely exceeds three feet. This, then, is the depth to which the soluble salts in the soil may be washed each successive year by the nat- ural rainfall; and from this depth it may partially or wholly reascend toward or to the surface by evaporation during each dry season. It is reasonable to expect that near the lower limit there will be a gradual accumulation of the saline matters, which reach it from above in the form of strong solutions. Plate 1 illustrates this strikingly. It shows the condition of the natural, unirrigated land at a point half a mile north of the Experi- ment Station, which was at the time (May 3, 1895) covered by the native spring growth of herbage and flowers, and which during the dry season shows no sign of alkali on the surface. Evidently, at the time represented here the winter rains had washed the alkali salts so far from the surface down into the subsoil, that the seeds had no difficulty in germinating near the surface; and as the growing herbs covered the ground, practically all the evaporation took place through the roots and leaves, and hence the alkali did not move upward to any great extent. The bulk of the roots only reached to the level (18 to 24 inches), where the impregnation is not strong enough to hurt them. The soil moisture in this upper layer being pretty nearly exhausted by the evaporation through the plants during their growth, evaporation from the soil itself could not, thereafter, bring any perceptible amount of salts to the sur- face. Thus the first rain would, next season, again enable the seeds to germinate without injury from the alkali, despite the heavy impregna- tion farther down; which is seen, in this case, to be greatest about the second half of the third foot. As a matter of course, not only the native growth, but also any crop of which a good stand has been obtained on an alkali soil, will similarly tend to diminish or prevent the rise of the alkali. Hence, a crop of alfalfa, once established, may flourish for years on ground that, so soon as it is left bare during the dry season for the fall sowing of a grain crop, may prove altogether too strong near the surface, and may kill the grain. From about the 35-inch level down we see a sudden and very rapid decrease of the salts, so that toward the end of the fourth foot they are reduced to little more than is shown at the end of the first foot from the surface. Those familiar with "black alkali" lands in the upper San Joaquin Valley will at once recognize the three-foot depth as the one at which, in punching, or in digging post-holes or ditches, a very tough, intract- able, clay hardpan is frequently encountered, which, when exposed to the air, soon becomes covered with abundance of white salts. This is the cause of the thick, loose layer of salts often seen alongside of irrigation ditches in the alkali regions. We see thus demonstrated, beyond any possible cavil, the correctness of the conclusion we have previously drawn from the examination of the bottom waters, viz.: that the bulk of the alkali salts is, even in natural alkali lands, accumulated within easy reach of the surface and of under- drains; and that, if this accumulation is once removed, no more, or at least \ 3 I fc J 1 1 12. /\ )j~ \ 7r ) 3-1 \ *~H f \ X T 3 S3 Ti'rsL- V Fooi- SeccKi V Tool- ^kird. \/~Tt VeptK of- Sifti Column. -> "Fourth. — 8 — not enough to do any harm, will come from below. This points to under- drainage as the ready and complete corrective of all alkali, as has been long ago recommended by us. But it does not therefore follow that the indiscriminate use of under- drainage is to be recommended, since, as we have abundantly shown, enormous amounts of valuable soil ingredients would thus run to waste. In the majority of cases other means, presently to be referred to, will accomplish the reclamation. EFFECTS OF IRRIGATION. Let us now see what effect irrigation, or the establishment of leaky ditches in a pervious soil, will produce in land circumstanced as shown in Plate 1. As regards the latter case, any one can see for himself that as the ditch water, filling up the land from below upward, comes in contact with the alkali-sodden subsoil or hardpan layer, it will dissolve the salts and carry them up toward the surface. Evaporation from the moistened surface will then go on all the year to a greater or less extent, and the alkali will keep steadily moving upward; until, in the course of a few years, the maximum will be found, not three feet below, but right at the surface. This is one phase of the " rise of the alkali," very easily understood in the light of Plate 1; and its outcome is graphically shown in Plate 3, which scarcely requires comment. This diagram shows the condition of land originally similar to that represented by Plate 1, which has been irrigated for four or five years, and, quite lately, has also been influenced by a neighboring leaky ditch, outside of the Station inclosure. Here we see that the alkali has moved bodily upward, and has accumulated near and at the surface to such a degree that any useful growth of ordinary crops has become impossible. Seeds sown (except those of salt bushes) are quickly corroded or "rotted" by such alkali as this, and fail to sprout; anything set out, ready-grown, may live while the rains last, but will be promptly killed by the corrosion of the root-crown, or lower end of the stem, from the effect of the strong solution formed around it whenever a light rain or heavy dew falls, even if the root should be able to resist the action of the alkali within the soil itself. It is not quite so easy to understand why surface irrigation should produce the same general result as the rise of the bottom water from below; and yet a little consideration readily explains it. Under irriga- tion the land receives many times more water than in its natural condition, but rarely enough to leach the alkali salts into the country drainage, even if the impervious hardpan layer did not stand in the way. Practically all this irrigation water therefore ultimately evapo- rates in the course of the year. As it penetrates the soil to a greater depth than the natural rainfall ever goes, it gradually dissolves the alkali salts in the subsoil, and in the progress of its evaporation throughout the season, carries them with it toward the surface, instead of leaving most of them accumulated at between two and three feet depth, as in the natural state. In the course of time, especially in orchards where the soil remains bare and therefore exposed to evapora- tion throughout the season, the accumulation near the surface becomes so great as to injure even the bark of full-grown trees and vines ; while — 9 — Dej?rk Lu.Y*.n. \rCh\J Foot — 10 — t o CO "3 £ a. Depth. of- Soil Col S " i 2 '■~\ — o •t )5» -"- «' — 3 ■*• ^*- — "♦- Z i i * J *-3 S % 3 US s! ^ ^ Z o J Si '-( M.7L -> Depict. o| r Soil Colu-vM-ri-3 -? — 11 — ordinary herbaceous vegetation becomes impossible. If the alkali should be of the "black" kind — i. *- 2j "l , ft "1 .* ■•••*•■•■ »n\ . a « IP a 7 V 4 S'3 / / .....^ f V._ / " © 4\ *'• -■- \ ^y ■3P *■ "S *< A \ \ "■orjV ' \ \ y s "6\ - \ \ X "V L » k 83. |\ A -J \ \ / \ \ i \ / \ * A / . + < * \/ , +* v. ■*>•* \ N^\ V,. ,*•* ^ I.I.T.. '"*""' *......., ! ..**>. **$■* "T" '"13 "±"*c \ 6 9 /■«-/ ^ «" /*- XI '^/ \f/ 30 r jj i JL J 7/ m/- v ' Too /- -Stc unJ » 7-oi »/- 7VW* ^ ? r ««/'- a Jo 5 .! •s *. t> a. W TiysI- ^ Foe/- -S<*««.«* V^ De/jfii of-rSotL Colum-ii — > ;f<>W- Too-trh.'-^F^F — 13 — COUNTERACTING EVAPORATION. From what has been said it is obvious that since evaporation from the soil surface is the cause of any u rise of the alkali" one of the chief pre- ventive measures must be the reduction of surface evaporation to the lowest possible point. This can be done either by mulching or, less effectually, by shading. The best mulch, available in all cases, is a well and deeply tilled sur- face soil, on which a crust is never allowed to form. Then evaporation will be reduced to the minimum, and whatever does take place leaves the alkali distributed through the whole of the tilled layer, instead of at the surface, where the bulk of the damage is usually done. For, a loosely tilled soil will take up little or no moisture from a denser or more compact subsoil, which it protects quite as effectually as would a straw mulch. Of course, the depth or thickness of this protective tilled layer is of the utmost importance, not only for the sake of preventing evaporation and accumulation, but also because, since the maximum of alkali in irrigated land at the end of the dry season is always near the surface, the intermixing of the strong surface alkali with as large a mass of subsoil as possible, is important in order to dilute and diffuse it; so that it may not be strong enough anywhere to hurt the roots or root-crown. After such an intermixture, say to the depth of ten or twelve inches, it takes some time to bring the salts to the surface again to a sufficient extent to hurt the crop. An instinctive recognition of this principle has led cultivators of alkali soils in some cases to resort to sanding the surface, and with temporary good results. But the mainstay in the cultivation of alkali land must always be the maintenance of deep and loose tilth throughout the times when evapora- tion is active. This implies the growing on them of hoed rather than grain crops, unless drill culture (which at present prices would hardly pay) were resorted to. The growing of corn, beans, beets, and possibly of canaigre, always choosing preferably the deep-rooted crops, is there- fore indicated; and experience at Chino has conclusively shown that the very best of beets may be grown on light alkali soils in which com- mon salt is not too prominent. Deep and loose tillage, however, is practically impossible on lands tainted with any considerable amount of "black" alkali. It will remain cloddy, and will crust over even with dew, despite all cultivating, har- rowing, and clod-crushing. The first need, therefore, is the neutraliza- tion of the black alkali with gypsum, by which operation other important benefits are also secured. The saving in cost of cultivation on heavier lands will alone soon pay for the purchase of the gypsum, aside from increased and improved products. It must always be remembered that little or no benefit is to be expected from gypsum in cases of purely <; white," neutral alkali; but there are tens of thousands of acres of land now lying idle, lightly tainted with "black" alkali, that would be definitely reclaimed, and rendered profusely productive, by the use, once for all, of a ton of gypsum per acre. But it is not absolutely necessary to use the entire amount at once; it can also be done by — 14 — annual installments of say five hundred pounds per acre, put in some time before the seed. The latter will thus be protected from being killed by the black alkali, and secure a stand to shade the ground, preventing an injurious rise of salts for the season at least. It must be remembered, however, that gypsum cannot act on alkali without water; and that the action itself takes several weeks before immunity is secured, and continues for several months, and even longer. The dressing of gypsum should therefore be applied in ample time before seeding, and after cultivating or plowing-in should be promptly followed by irrigation, unless the rainy season can be relied upon to perform the service before seeding time. The smaller the seed to be sown the more important is this precaution; beans, peas, or maize may remain unharmed where alfalfa, or other clover seeds, as well as those of meadow and pasture grasses, would perish either before or during germination. One additional point should be emphasized here. It will be seen from the curve lines representing the individual salts — common and Glauber's salt, and sal soda — that the latter is proportionally most abundant in the clay hardpan (Plate 1), where it forms from 80 to over 90 per cent of the whole; while near the surface, in the very same bore- hole, it forms about 23 per cent only. This is due to the moisture and want of aeration in the subsoil, acting in a manner not easily explained in a popular way. But it may be taken for granted that whenever an alkali soil is subjected to the action of stagnant water, or of abundant moisture without aeration, the formation of black alkali will take place. This is the reason why the latter is most commonly found in low, moist ground, and in close, heavy soils; while on the higher ground adjacent the white salts alone may prevail. The " swamping " of alkali lands is thus seen to be doubly pernicious; and the leaky ditches which cause it should, for this reason alone, be considered a public nuisance.