In irrigated regions, there is a conviction that the best agriculture, and therefore the best country life, is to develop in arid America. This is a result of the belief that a completer and exacter control of the land can be secured by means of irrigation than by relying on the uncertainties of rainfall. Many persons think that the only really predictable and dependable agriculture must rest on irrigation. It is true that a dependable irrigation reduces one of the great elements of uncertainty and risk; but not all irrigation is dependable in the amount and quality of water, and the extent of land that can be brought into cultivation solely on irrigationsupply of water is relatively small. It is a fair question whether the highest skill may not be required in those regions in which the elements of risk are most numerous, for the greater the number of the problems the more alert and resourceful must the farmer be. At all events, the humid regions must be cultivated; but in these very regions, one of the largest risks will be removed by supplementary irrigation. The question, then, in these humid regions will be not only the adding of water at certain times of the year but the removing of superfluous water at other times irrigation and drainage will be coördinate practices. Fig. 558. Artesian irrigation. A reservoir near St. Davids, Arizona, for collecting the flow of three small artesian wells, securing a large head of water for irrigation. The days of pioneering in the old way are now practically done. The irrigation systems worked out by the Mormons and others have shown the way for the development of most of the farther West. This experience has now culminated in the national Reclamation Act, setting aside sales of public lands for the constructing of irrigation works. This act was signed by President Roosevelt June 17, 1902. This signalizes a system of national undertakings comparable, in many ways, with the river and harbor improvements. It has also put the moral support of the nation behind the development of the West; and it is easy for the political philosopher to follow out what some of the consequences are likely to be. It is not to be expected that the national reclamation service is to reclaim to cultivation all of the arid West, or even any considerable part of it; but in setting its machinery at work, it has also stimulated the discussion of all the questions that center about irrigation, and, therefore, around the development of the western country, and is helping to take this development out of haphazard and pioneer and propagandic methods into ways of permanent orderly procedure. The irrigation movement has now reached its educational and scientific phase. A definite line of policy in respect to settlement of reclaimed lands was voiced by President Roosevelt in his message to the Thirteenth National Irrigation Congress, at Portland, in 1905, and also by President Pardee, Governor of California, in his presidential address, and re-echoed at many times and in many ways during the convention. In President Roosevelt's language, it is this: "No man should be permitted to take or occupy more of the public land than he can put to beneficial use. And so far as it can be done with safety to the great interests of the nation, every man who will put public land to its highest use by making his permanent home upon it should be allowed to take enough of it to support that home, of course under the necessary restrictions." Governor Pardee stated the subject thus: "The economic welfare of the whole country is involved, for the ultimate object to be attained is the upbuilding of national prosperity upon the most enduring of all foundations: the largest possible increase in the number of small property owners and the multiplication of homes." The tone of the convention was wholly removed from land-grabbing schemes or mere "promoting" enterprises: the West must grow and improve, and the irrigation service is the result of a perfectly normal natural development. No such tremendous areas of land will be suddenly thrown on the market, to the upset of eastern agriculture, as many per Fig. 559. Irrigation of a garden. The water from the Gila River is carried through furrows. Prima, Arizona. sons have feared. The areas that can be reclaimed are, after all, relatively small; and the expansion may be expected to be nearly all absorbed by the natural growth of the West itself. A most impressive note in the irrigation conventions and congresses is the forward look and the spiritual significance of the gatherings. This note signifies how fundamental are the questions involved in the discussions. One could not hear the great Mormon chorus of more than two hundred voices rendering the "Irrigation Ode" at Portland, with mighty volume and swing, without feeling that in arid America a new kind of poetry and literature is to be born and a new direction is to be given to some of the currents of civilization. One feels that this western civilization is fastened directly to the land, and that the effort is always to stand on the soil; and it therefore has an indigenousness and nativeness that one vainly longs for in many other countries. It is inspiring to hear an ode on the actual affairs whereby men subsist. Two stanzas from the Irrigation Ode, by Mrs. Gilbert McClurg, will show its spirit. The first stanza is "The Desert": The land of the smiting sun-glare, deep-blue of the star-pierced night, Of rock-piled heights and chasms, awe-fraught to the dizzying sight, With purple and pink and crimson, opalescent and far away! The candlesticks of the cactus flame-torches here up-hold; Sunflower disks and feath'ry mustard spread fields of the cloth of gold. When the desert wind arises,-and they fade as they are born! The rainbow-colored spaces, wan and withered in a breath;- Life of sky and sand awaking to prey when all is done; Land of the desolate people, born of sirocco and sun! (Recitative) Oh! desert land! The land of homes for the homeless; of shepherded flocks and herds; Of the faith that sees in the desert the promise of verdant blades, Where, on glimmering heights of future, gleam fair regenerate years, In the garden grows the Tree of Life where Eden's rivers run, THE MOISTURE OF THE SOIL By J. A. Bonsteel The importance of a proper amount of soil moisture in crop production cannot be overestimated. The higher plant forms, which constitute the forage, grain and food crops of the country, are able to secure their nourishment from the soil only through the medium of the soil moisture and of the material which is dissolved in it. The same plants, though abundantly supplied with dissolved plantfood, cannot live unless relatively large amounts of soil water are taken from the ground, carried through the plant and evaporated at the surface of the leaves. The failure to perform these two functions gives rise to the respective results of plant starvation and drought. Soil moisture also performs other functions, such as the equalization of soil temperatures, the distribution of soluble fertilizing materials, the maintenance of chemical and physical activities, and even the function of controlling in a measure the bacterial life of the soil. The dissipation of rain-water. The common source of soil moisture is rainwater. When the moisture of the air condenses into drops and falls to the surface of the ground its fall seems to be stopped, but is in reality only retarded. A part of the rain-water is speedily A third part of the rainfall passes slowly into the soil. It is a mistake to suppose that it sinks into the soil through the innumerable pore spaces which exist between the individual soil grains, or that these pore spaces are filled until the soil is saturated. On the contrary, in the case of all of the heavier clays and loams, in fact in all but the most porous sands, the rainfall penetrates the soil chiefly through cracks, joints, crevices, angleworm burrows and the tubular spaces left by the decay of plant roots. Only a gentle, long-continued "soaking" rain is capable of utilizing fully the many avenues of circulation presented by the average arable soil. However, when the atmospheric moisture has begun its career as soil moisture by passing into the larger openings, it speedily soaks into the mass of the soil through the smaller pore spaces that are found in even the stiffest clays. In a majority of cases even a large rainfall is rapidly absorbed within the surface six inches or one foot of ordinary cultivated soils. Some part of the water does not cease its movement at this stage. It continues to fall through the larger openings until it meets with some less pervious layer of clay or with rock. It may then flow away along the surface of such a stratum, finally escaping at a lower level in the form of springs, or it may be denied such an outlet and accumulate as ground water. When the ground water approaches near to the surface the land is called boggy or wet. When it reaches the surface, a swamp, a spring, or a lake may be formed. The water that runs off the surface is of little use to vegetation. That which forms springs by flowing far under ground is usually of small value to growing plants. That which accumulates as swamps or marshy spots is of positive harm to all but a few species of cultivated plants. So far as agriculture is concerned, it is the relatively small amount of moisture that remains absorbed in the partially dry surface layers of the soil on which crops depend not only for their water-supply, but also for their supply of mineral plant-food. This soil moisture usually forms rather thin films surrounding the small soil grains and occupying the small angles where they touch. This moisture is in contact on one side with the mineral and dead organic matter of the soil and on the other with the soil air which almost always occupies a large part of the open porous space in the soil. When plants are growing on a soil, their roots and root-hairs are also in contact with the soil, the soil moisture and the soil air. The function of the soil moisture. As a solvent. The rôle played by soil moisture is extremely complex. No water which falls on the soil is pure. During its passage through the air as rain it has absorbed small but measurable amounts of carbonic acid gas, ammonia and oxygen, besides WHEAT LAND EARLY TRUCK LAND • a b c b c d co o d d d d d d a c d d la d d e bll Fig. 560. Water content of typical soils. Soil moisture actually found in thirty samples of wheat soils and in twenty-eight samples of truck soils. Figures at left (5, 10, 15) indicate percentage of moisture by weight. other impurities. When it comes in contact with vegetation and particularly with the decaying litter found on the surface of almost all soils, it takes on more carbonic acid gas and also certain other weak acids that are the product of vegetable decay. Thus armed, it sinks into the soil in the form of an active solvent of many materials. Almost all of the minerals that compose soils may be dissolved by water that is chemically pure. There are no known minerals occurring in the soils that cannot be dissolved to some extent by the impure water that enters the soil after a rain. Even those minerals, like feldspar, which are least soluble directly, are chemically attacked by the soil water and by the impurities which it bears, so that their store of material suitable to form plant-food is slowly but surely and continuously liberated. In this way the supply of plant-food is derived from the mineral matter of the soil, and few known soils are so simple mineralogically or so difficult of solution but that plenty of water properly supplied is able to continue to unlock plant-food at a rate sufficiently rapid to nourish plants. Whether plants can grow on soil depends on a variety of other factors, some of which are totally unconnected with the soil itself. As a carrier.-Soil moisture is required to transport plant-food into the plant as well as to prepare the food for presentation to the plant. This transportation may be accomplished in a variety of ways. The water and the plant-food dissolved in it may pass bodily into the plant-tissues to supply the place of the water evaporated from the leaves. The water after evaporation is pure, or distilled water. The impurities, whether helpful or harmful to plant-life, remain behind to be disposed of by the plant. Again, the dissolved material in the soil moisture may pass into the plant-tissues independently of any movement of water or in a contrary direction to that of water movement, just as a lump of salt placed in the bottom of a tumbler of water will dissolve and its particles pass to all parts of the water of the tumbler. This process is known as diffusion, and it plays an extremely important part in plant feeding. Whenever the amount of any dissolved matter in the soil moisture is reduced through diffusion and its use by the plant, the soil moisture gains new power to dissolve more mineral matter of the same kind to take its place, so that the soil moisture is capable of continually replacing the used material by further solution of the mineral matter of the soil. This is one of the chief functions of soil moisture and one which is just coming to be understood. To maintain turgidity.-All growing plants require water to distend the many cells of which they are composed and thus to maintain the plant Fig. 561. Moisture determined by the method of drying samples. A comparison of the weights before and after drying gives the amount of moisture in the soil. This method may be used by the farmer to determine the moisture. A tin cup full of soil can be dried in an ordinary oven; the loss of weight constitutes the moisture lost. against what is called wilting. An immense amount of water is evaporated constantly from the large total surface of the leaves, and this water must be re-supplied from the soil moisture. It has been estimated that in order to produce a full crop of any one of the cereal grains at least 250 pounds of water must be supplied for every pound of dry matter produced, both stalk and grain. It would then require 200 tons of water to produce the grain alone of 30 bushels of wheat. The straw would require as much more, while the roots and stubble would also need to be provided for. Of course the amount of moisture required to prevent drought or wilting varies with the kind of crop, the character of the climate and the texture of the soil. Oats and corn require large amounts of moisture, potatoes smaller amounts. More water is normally required when the air around the plants is dry than when it is wet. No two soils have the same characteristics in regard to the rapidity with which they can supply water to plants, nor in regard to the total amount they must contain to remain above the drought limit. Moreover, the same individual plant requires water supplied more rapidly at some stages of its growth than at others. The effect on temperature. The soil moisture exerts another very important influence through its effect on the temperature of soils. It is a fact that five times as much heat, or even more, is required to warm one cubic foot of water as is required to warm equally one cubic foot of soil. Thus a saturated, water-logged soil is always spoken of as a "cold, wet soil." Such soils are late to germinate seed, since most seeds must be warmed above 45° F. before they can sprout, and plant growth is favored by temperatures ranging from 60° to 80° F. "A hot, wet day makes corn grow," is a familiar saying in some sections of the country. Soil saturation. The excess of water must be removed from a saturated soil before ordinary farm crops can grow. This may be accomplished by drainage, but too frequently this is not provided and the sun is depended on to evaporate the water. It requires nearly one thousand times as much heat to evaporate one cubic foot of water as it does to raise the temperature of the same mass one degree in temperature, so that the loss of heat energy experienced in warming and drying the saturated soils of the United States in one year, represents an enormous amount of horse-power if it could be so calculated. A proper amount of soil moisture helps to preserve the soil from overheating during the burning days of the dry summer, just as free perspiration preserves a man from sunstroke; but more soils are suffering from an excess of moisture than from a lack of it in the humid regions of the United States. An excess of soil moisture is present whenever the pore-spaces of a soil are clogged with water. In this condition the soil is hermetically sealed against the entrance of air, as was the milk in certain old, deep-setting cream cans. Every part of a plant which is growing, that is, which is forming new plant-cells and enlarging its tissues, must have free access to oxygen, and the air is one source of that element. Consequently, the saturation of a soil and the resulting exclusion of fresh supplies of air must result in stunted plantgrowth or in the death of the plant. Even eel-grass grows only when it is exposed above tide for a part of the day; and the cypress sends its knees above water-level even when submerged only a part of the year. Cypress trees on dry land have no knees. The conservation or saving of moisture. The importance of soil moisture is plainly evident. The proper methods for its maintenance and control are among the most fundamental problems in soil management and farm practice. Plowing and cultivation are processes intended to prepare a seed-bed for germinating and growing plants. At the same time, they are the most common methods of providing for the accumulation, storage and retention of soil moisture. Rain Fig. 562. Electrical apparatus for field determination of moisture in soils. Electrodes are buried in the ground at various depths in different parts of the field, and readings of the moisture conditions may be taken daily to secure a record of the moisture at different depths over an entire field. (This method is used chiefly for research work.) 66 falling on a puddled clay surface runs off. That is why tiles are used as roof coverings. If the puddled clay surface is carefully plowed, so that a fine, porous layer of dirt is formed, as mellow as an ash heap," a much greater amount of moisture is absorbed and retained by the soil, its distribution is more even, and the washing away of valuable surface soil is largely prevented. If, after the rain has fallen on a properly prepared soil, the sun comes out and burns and bakes a crust on the surface, a large amount of water may be evaporated into the air before the growing plants have had an opportunity to use it. But if the crust be broken and the surface soil stirred to a shallow depth, a mulch is formed which not only reduces the rate of evaporation but which causes it to take place well down within the soil rather than at the surface, and it has been pointed out that when the evaporation takes place there the dissolved plant-food is left in the soil in the proper place. Proper cultivation also aids the plant materially in securing its supply of moisture by allowing its roots greater freedom. The subsoil below plowing depth is usually much more compact and much less porous than the fined and mellowed surface soil. As a result, plant-roots develop and spread to the best advantage down to the normal depth of plowing. Below that, "hardpan" is frequently struck. Proper plowing to a good depth not only increases the total reservoir space for storing soil moisture, but it also allows the roots to spread widely and freely to all points where moisture and food and air, the three essentials of plantlife, may be secured. The removal of excess moisture. Excess moisture can be removed only by drainage. In many cases it is necessary to dispose of temporary surface excesses of water only. For this purpose, shallow open ditches of broad U-shaped contour may best be employed. Teams and tools can be driven across them. Crops may grow in them while they are not performing their duties as drains. Frost and flood do not cave in their sides as is the case with steep-sided ditches. [This subject is discussed in Professor King's article, following.] Summary. In conclusion, the dominant facts connected with the problem of soil moisture may be summarized briefly : (1) Soil moisture is an essential part or factor of the soil, since it prepares and distributes the foodsupply of plants. (2) Soil moisture largely dominates the temperature of soils, and hence influences the vitality of seeds and plants. (3) Soil moisture admits air to the soil or excludes it, and all growing parts of a plant must have air with the oxygen it contains. (4) Moisture in slow motion in the soil and not saturating it is uniformly beneficial to plant-life even in large amounts. (5) Moisture stagnant in soils, or saturating them, though in motion, is uniformly harmful to all plants except especially adapted swamp species. (6) The problem of securing, distributing, conserving and supplying soil moisture is a fundamental problem in agriculture, and many failures in farm management may be traced directly to a failure on the part of the farmer to understand or to solve this problem. (7) The control of the kind and the amount of crops raised on the ordinary soil is so closely related to the control of soil moisture that this one factor in crop-production is the dominant factor in all ordinary agriculture. This is well known in irrigated areas. Literature. The subject of soil moisture is considered to some extent in most general works on soils, and the literature is varied and scattered. Specific treatment of the subject will be found in the following: Various papers of United States Geological Survey, Hydrographic Division; How Crops Grow, by S. W. Johnson; The Soil, by F. H. King; Physical Properties of Soils, by R. Warington; Mechanics of Soil Moisture, by L. J. Briggs, Bulletin No. 10, Bureau of Soils, United States Department of Agriculture; Investigations in Soil Fertility, Whitney & Cameron, Bulletin No. 23, Bureau of Soils; Mineral Constituents of the Soil Solution, Bulletin No. 30, Bureau of Soils. |