CHAPTER VII
STORING WATER IN THE SOIL


THE large amount of water required for the productionof plant substance is taken from the soil by the roots. Leaves and stems do not absorbappreciable quantities of water. The scanty rainfall of dry-farm districts or themore abundant precipitation of humid regions must, therefore, be made to enter thesoil in such a manner as to be readily available as soil-moisture to the roots atthe right periods of plant growth.

In humid countries, the rain that falls duringthe growing season is looked upon, and very properly, as the really effective factorin the production of large crops. The root systems of plants grown under such humidconditions are near the surface, ready to absorb immediately the rains that fall,even if they do not soak deeply into the soil. As has been shown in Chapter IV, itis only over a small portion of the dry-farm territory that the bulk of the scantyprecipitation occurs during the growing season. Over a large portion of the aridand semiarid region the summers are almost rainless and the bulk of the precipitationcomes in the winter, late fall, or early spring when plants are not growing. If therains that fall during the growing season are indispensable in crop production, thepossible area to be reclaimed by dry-farming will be greatly limited. Even when muchof the total precipitation comes in summer, the amount in dry-farm districts is seldomsufficient for the proper maturing of crops. In fact, successful dry-farming dependschiefly upon the success with which the rains that fall during any season of theyear may be stored and kept in the soil until needed by plants in their growth. Thefundamental operations of dry-farming include a soil treatment which enables thelargest possible proportion of the annual precipitation to be stored in the soil.For this purpose, the deep, somewhat porous soils, characteristic of arid regions,are unusually well adapted.


Alway's demonstration

An important and unique demonstration of thepossibility of bringing crops to maturity on the moisture stored in the soil at thetime of planting has been made by Alway. Cylinders of galvanized iron, 6 feet long,were filled with soil as nearly as possible in its natural position and conditionWater was added until seepage began, after which the excess was allowed to drainaway. When the seepage had closed, the cylinders were entirely closed except at thesurface. Sprouted grains of spring wheat were placed in the moist surface soil, and1 inch of dry soil added to the surface to prevent evaporation. No more water wasadded; the air of the greenhouse was kept as dry as possible. The wheat developednormally. The first ear was ripe in 132 days after planting and the last in 143 days.The three cylinders of soil from semiarid western Nebraska produced 37.8 grams ofstraw and 29 ears, containing 415 kernels weighing 11.188 grams. The three cylindersof soil from humid eastern Nebraska produced only 11.2 grams of straw and 13 earscontaining 114 kernels, weighing 3 grams. This experiment shows conclusively thatrains are not needed during the growing season, if the soil is well filled with moistureat seedtime, to bring crops to maturity.


What becomes of the rainfall ?

The water that falls on the land is disposedof in three ways: First, under ordinary conditions, a large portion runs off withoutentering the soil; secondly, a portion enters the soil, but remains near the surface,and is rapidly evaporated back into the air; and, thirdly, a portion enters the lowersoil layers, from which it is removed at later periods by several distinct processes.The run-off is usually large and is a serious loss, especially in dry-farming regions,where the absence of luxuriant vegetation, the somewhat hard, sun-baked soils, andthe numerous drainage channels, formed by successive torrents, combine to furnishthe rains with an easy escape into the torrential rivers. Persons familiar with aridconditions know how quickly the narrow box cañons, which often drain thousandsof square miles, are filled with roaring water after a comparatively light rainfall.


The run-off

The proper cultivation of the soil diminishesvery greatly the loss due to run-off, but even on such soils the proportion may oftenbe very great. Farrel observed at one of the Utah stations that during a torrentialrain--2.6 inches in 4 hours--the surface of the summer fallowed plats was packedso solid that only one fourth inch, or less than one tenth of the whole amount, soakedinto the soil, while on a neighboring stubble field, which offered greater hindranceto the run-off, 1-1/2 inches or about 60 per cent were absorbed.

It is not possible under any condition to preventthe run-off altogether, although it can usually be reduced exceedingly. It is a commondry-farm custom to plow along the slopes of the farm instead of plowing up and downthem. When this is done, the water which runs down the slopes is caught by the successionof furrows and in that way the runoff is diminished. During the fallow season thedisk and smoothing harrows are run along the hillsides for the same purpose and withresults that are nearly always advantageous to the dry-farmer. Of necessity, eachman must study his own farm in order to devise methods that will prevent the run-off.


The structure of soils

Before examining more closely the possibilityof storing water in soils a brief review of the structure of soils is desirable.As previously explained, soil is essentially a mixture of disintegrated rock andthe decomposing remains of plants. The rock particles which constitute the majorportion of soils vary greatly in size. The largest ones are often 500 times the sizesof the smallest. It would take 50 of the coarsest sand particles, and 25,000 of thefinest silt particles, to form one lineal inch. The clay particles are often smallerand of such a nature that they cannot be accurately measured. The total number ofsoil particles in even a small quantity of cultivated soil is far beyond the ordinarylimits of thought, ranging from 125,000 particles of coarse sand to 15,625,000,000,000particles of the finest silt in one cubic inch. In other words, if all the particlesin one cubic inch of soil consisting of fine silt were placed side by side, theywould form a continuous chain over a thousand miles long. The farmer, when he tillsthe soil, deals with countless numbers of individual soil grains, far surpassingthe understanding of the human mind. It is the immense number of constituent soilparticles that gives to the soil many of its most valuable properties.

It must be remembered that no natural soil ismade up of particles all of which are of the same size; all sizes, from the coarsestsand to the finest clay, are usually present. These particles of all sizes are notarranged in the soil in a regular, orderly way; they are not placed side by sidewith geometrical regularity; they are rather jumbled together in every possible way.The larger sand grains touch and form comparatively large interstitial spaces intowhich the finer silt and clay grains filter. Then, again, the clay particles, whichhave cementing properties, bind, as it were, one particle to another. A sand grainmay have attached to it hundreds, or it may be thousands, of the smaller silt grains;or a regiment of smaller soil grains may themselves be clustered into one large grainby cementing power of the clay. Further, in the presence of lime and similar substances,these complex soil grains are grouped into yet larger and more complex groups. Thebeneficial effect of lime is usually due to this power of grouping untold numbersof soil particles into larger groups. When by correct soil culture the individualsoil grains are thus grouped into large clusters, the soil is said to be in goodtilth. Anything that tends to destroy these complex soil grains, as, for instance,plowing the soil when it is too wet, weakens the crop-producing power of the soil.This complexity of structure is one of the chief reasons for the difficulty of understandingclearly the physical laws governing soils.


Pore-space of soils

It follows from this description of soil structurethat the soil grains do not fill the whole of the soil space. The tendency is ratherto form clusters of soil grains which, though touching at many points, leave comparativelylarge empty spaces. This pore space in soils varies greatly, but with a maximum ofabout 55 per cent. In soils formed under arid conditions the percentage of pore-spaceis somewhere in the neighborhood of 50 per cent. There are some arid soils, notablygypsum soils, the particles of which are so uniform size that the pore-space is exceedinglysmall. Such soils are always difficult to prepare for agricultural purposes.

It is the pore-space in soils that permits thestorage of soil- moisture; and it is always important for the farmer so to maintainhis soil that the pore-space is large enough to give him the best results, not onlyfor the storage of moisture, but for the growth and development of roots, and forthe entrance into the soil of air, germ life, and other forces that aid in makingthe soil fit for the habitation of plants. This can always be best accomplished,as will be shown hereafter, by deep plowing, when the soil is not too wet, the exposureof the plowed soil to the elements, the frequent cultivation of the soil throughthe growing season, and the admixture of organic matter. The natural soil structureat depths not reached by the plow evidently cannot be vitally changed by the farmer.


Hygroscopic soil-water

Under normal conditions, a certain amount ofwater is always found in all things occurring naturally, soils included. Clingingto every tree, stone, or animal tissue is a small quantity of moisture varying withthe temperature, the amount of water in the air, and with other well-known factors.It is impossible to rid any natural substance wholly of water without heating itto a high temperature. This water which, apparently, belongs to all natural objectsis commonly called hygroscopic water. Hilgard states that the soils of the arid regionscontain, under a temperature of 15° C. and an atmosphere saturated with water,approximately 5-1/2 per cent of hygroscopic water. In fact, however, the air overthe arid region is far from being saturated with water and the temperature is evenhigher than 15° C., and the hygroscopic moisture actually found in the soilsof the dry-farm territory is considerably smaller than the average above given. Underthe conditions prevailing in the Great Basin the hygroscopic water of soils variesfrom .75 per cent to 3-1/2 per cent; the average amount is not far from 12 per cent.

Whether or not the hygroscopic water of soilsis of value in plant growth is a disputed question. Hilgard believes that the hygroscopicmoisture can be of considerable help in carrying plants through rainless summers,and further, that its presence prevents the heating of the soil particles to a pointdangerous to plant roots. Other authorities maintain earnestly that the hygroscopicsoil-water is practically useless to plants. Considering the fact that wilting occurslong before the hygroscopic water contained in the soil is reached, it is very unlikelythat water so held is of any real benefit to plant growth.


Gravitational water

It often happens that a portion of the waterin the soil is under the immediate influence of gravitation. For instance, a stonewhich, normally, is covered with hygroscopic water is dipped into water The hydroscopicwater is not thereby affected, but as the stone is drawn out of the water a goodpart of the water runs off. This is gravitational water That is, the gravitationalwater of soils is that portion of the soil-water which filling the soil pores, flowsdownward through the soil under the influence of gravity. When the soil pores arecompletely filled, the maximum amount of gravitational water is found there. In ordinarydry-farm soils this total water capacity is between 35 and 40 per cent of the dryweight of soil.

The gravitational soil-water cannot long remainin that condition; for, necessarily, the pull of gravity moves it downward throughthe soil pores and if conditions are favorable, it finally reaches the standing water-table,whence it is carried to the great rivers, and finally to the ocean. In humid soils,under a large precipitation, gravitational water moves down to the standing water-tableafter every rain. In dry-farm soils the gravitational water seldom reaches the standingwater-table; for, as it moves downward, it wets the soil grains and remains in thecapillary condition as a thin film around the soil grains.

To the dry-farmer, the full water capacity isof importance only as it pertains to the upper foot of soil. If, by proper plowingand cultivation, the upper soil be loose and porous, the precipitation is allowedto soak quickly into the soil, away from the action of the wind and sun. From thistemporary reservoir, the water, in obedience to the pull of gravity, will move slowlydownward to the greater soil depths, where it will be stored permanently until neededby plants. It is for this reason that dry-farmers find it profitable to plow in thefall, as soon as possible after harvesting. In fact, Campbell advocates that theharvester be followed immediately by the disk, later to be followed by the plow Theessential thing is to keep the topsoil open and receptive to a rain.


Capillary soil-water

The so-called capillary soil-water is of greatestimportance to the dry-farmer. This is the water that clings as a film around a marblethat has been dipped into water. There is a natural attraction between water andnearly all known substances, as is witnessed by the fact that nearly all things maybe moistened. The water is held around the marble because the attraction betweenthe marble and the water is greater than the pull of gravity upon the water. Thegreater the attraction, the thicker the film; the smaller the attraction, the thinnerthe film will be. The water that rises in a capillary glass tube when placed in waterdoes so by virtue of the attraction between water and glass. Frequently, the forcethat makes capillary water possible is called surface tension.

Whenever there is a sufficient amount of wateravailable, a thin film of water is found around every soil grain; and where the soilgrains touch, or where they are very near together, water is held pretty much asin capillary tubes. Not only are the soil particles enveloped by such a film, butthe plant roots foraging in the soil are likewise covered; that is, the whole systemof soil grains and roots is covered, under favorable conditions, with a thin filmof capillary water. It is the water in this form upon which plants draw during theirperiods of growth. The hygroscopic water and the gravitational water are of comparativelylittle value in plant growth.


Field capacity of soils for capillary water

The tremendously large number of soil grainsfound in even a small amount of soil makes it possible for the soil to hold verylarge quantities of capillary water. To illustrate: In one cubic inch of sand soilthe total surface exposed by the soil grains varies from 42 square inches to 27 squarefeet; in one cubic inch of silt soil, from 27 square feet to 72 square feet, andin one cubic inch of an ordinary soil the total surface exposed by the soil grainsis about 25 square feet. This means that the total surface of the soil grains containedin a column of soil 1 square foot at the top and 10 feet deep is approximately 10acres. When even a thin film of water is spread over such a large area, it is clearthat the total amount of water involved must be large It is to be noticed, therefore,that the fineness of the soil particles previously discussed has a direct bearingupon the amount of water that soils may retain for the use of plant growth. As thefineness of the soil grains increases, the total surface increases' and the water-holdingcapacity also increases.

Naturally, the thickness of a water film heldaround the soil grains is very minute. King has calculated that a film 275 millionthsof an inch thick, clinging around the soil particles, is equivalent to 14.24 percent of water in a heavy clay; 7.2 per cent in a loam; 5.21 per cent in a sandy loam,and 1.41 per cent in a sandy soil.

It is important to know the largest amount ofwater that soils can hold in a capillary condition, for upon it depend, in a measure,the possibilities of crop production under dry-farming conditions. King states thatthe largest amount of capillary water that can be held in sandy loams varies from17.65 per cent to 10.67 per cent; in clay loams from 22.67 per cent to 18.16 percent, and in humus soils (which are practically unknown in dry-farm sections) from44.72 per cent to 21.29 per cent. These results were not obtained under dry-farmconditions and must be confirmed by investigations of arid soils.

The water that falls upon dry-farms is very seldomsufficient in quantity to reach the standing water-table, and it is necessary, therefore,to determine the largest percentage of water that a soil can hold under the influenceof gravity down to a depth of 8 or 10 feet--the depth to which the roots penetrateand in which root action is distinctly felt. This is somewhat difficult to determinebecause the many conflicting factors acting upon the soil-water are seldom in equilibrium.Moreover, a considerable time must usually elapse before the rain-water is thoroughlydistributed throughout the soil. For instance, in sandy soils, the downward descentof water is very rapid; in clay soils, where the preponderance of fine particlesmakes minute soil pores, there is considerable hindrance to the descent of water,and it may take weeks or months for equilibrium to be established. It is believedthat in a dry-farm district, where the major part of the precipitation comes duringwinter, the early springtime, before the spring rains come, is the best time fordetermining the maximum water capacity of a soil. At that season the water-dissipatinginfluences, such as sunshine and high temperature, are at a minimum, and a sufficienttime has elapsed to permit the rains of fall and winter to distribute themselvesuniformly throughout the soil. In districts of high summer precipitation, the latefall after a fallow season will probably be the best time for the determination ofthe field-water capacity.

Experiments on this subject have been conductedat the Utah Station. As a result of several thousand trials it was found that, inthe spring, a uniform, sandy loam soil of true arid properties contained, from yearto year, an average of nearly 16-1/2 per cent of water to a depth of 8 feet. Thisappeared to be practically the maximum water capacity of that soil under field conditions,and it may be called the field capacity of that soil for capillary water. Other experimentson dry-farms showed the field capacity of a clay soil to a depth of 8 feet to be19 per cent; of a clay loam, to be 18 per cent; of a loam, 17 per cent; of anotherloam somewhat more sandy, 16 per cent; of a sandy loam, 14-1/2 per cent; and of avery sandy loam, 14 per cent. Leather found that in the calcareous arid soil of Indiathe upper 5 feet contained 18 per cent of water at the close of the wet season.

It may be concluded, therefore, that the field-watercapacities of ordinary dry-farm soils are not very high, ranging from 15 to 20 percent, with an average for ordinary dry-farm soils in the neighborhood of 16 or 17per cent. Expressed in another way this means that a layer of water from 2 to 3 inchesdeep can be stored in the soil to a depth of 12 inches. Sandy soils will hold lesswater than clayey ones. It must not be forgotten that in the dry-farm region arenumerous types of soils, among them some consisting chiefly of very fine soil grainsand which would; consequently, possess field-water capacities above the average herestated. The first endeavor of the dry-farmer should be to have the soil filled toits full field-water capacity before a crop is planted.


Downward movement of soil-moisture

One of the chief considerations in a discussionof the storing of water in soils is the depth to which water may move under ordinarydry-farm conditions. In humid regions, where the water table is near the surfaceand where the rainfall is very abundant, no question has been raised concerning thepossibility of the descent of water through the soil to the standing water. Considerableobjection, however, has been offered to the doctrine that the rainfall of arid districtspenetrates the soil to any great extent. Numerous writers on the subject intimatethat the rainfall under dry-farm conditions reaches at the best the upper 3 or 4feet of soil. This cannot be true, for the deep rich soils of the arid region, whichnever have been disturbed by the husbandman, are moist to very great depths. In thedeserts of the Great Basin, where vegetation is very scanty, soil borings made almostanywhere will reveal the fact that moisture exists in considerable quantities tothe full depth of the ordinary soil auger, usually 10 feet. The same is true forpractically every district of the arid region.

Such water has not come from below, for in themajority of cases the standing water is 50 to 500 feet below the surface. Whitneymade this observation many years ago and reported it as a striking feature of agriculturein arid regions, worthy of serious consideration. Investigations made at the UtahStation have shown that undisturbed soils within the Great Basin frequently contain,to a depth of 10 feet, an amount of water equivalent to 2 or 3 years of the rainfallwhich normally occurs in that locality. These quantities of water could not be foundin such soils, unless, under arid conditions, water has the power to move downwardto considerably greater depths than is usually believed by dry-farmers.

In a series of irrigation experiments conductedat the Utah Station it was demonstrated that on a loam soil, within a few hours afteran irrigation, some of the water applied had reached the eighth foot, or at leasthad increased the percentage of water in the eighth foot. In soil that was alreadywell filled with water, the addition of water was felt distinctly to the full depthof 8 feet. Moreover, it was observed in these experiments that even very small rainscaused moisture changes to considerable depths a few hours after the rain was over.For instance, 0.14 of an inch of rainfall was felt to a depth of 2 feet within 3hours; 0.93 of an inch was felt to a depth of 3 feet within the same period.

To determine whether or not the natural winterprecipitation, upon which the crops of a large portion of the dry-farm territorydepend, penetrates the soil to any great depth a series of tests were undertaken.At the close of the harvest in August or September the soil was carefully sampledto a depth of 8 feet, and in the following spring similar samples were taken on thesame soils to the same depth. In every case, it was found that the winter precipitationhad caused moisture changes to the full depth reached by the soil auger. Moreover,these changes were so great as to lead the investigators to believe that moisturechanges had occurred to greater depths.

In districts where the major part of the precipitationoccurs during the summer the same law is undoubtedly in operation; but, since evaporationis most active in the summer, it is probable that a smaller proportion reaches thegreater soil depths. In the Great Plains district, therefore, greater care will haveto be exercised during the summer in securing proper water storage than in the GreatBasin, for instance. The principle is, nevertheless, the same. Burr, working underGreat Plains conditions in Nebraska, has shown that the spring and summer rains penetratethe soil to the depth of 6 feet, the average depth of the borings, and that it undoubtedlyaffects the soil-moisture to the depth of 10 feet. In general, the dry-farmer maysafely accept the doctrine that the water that falls upon his land penetrates thesoil far beyond the immediate reach of the sun, though not so far away that plantroots cannot make use of it.


Importance of a moist subsoil

In the consideration of the downward movementof soil-water it is to be noted that it is only when the soil is tolerably moistthat the natural precipitation moves rapidly and freely to the deeper soil layers.When the soil is dry, the downward movement of the water is much slower and the bulkof the water is then stored near the surface where the loss of moisture goes on mostrapidly. It has been observed repeatedly in the investigations at the Utah Stationthat when desert land is broken for dry-farm purposes and then properly cultivated,the precipitation penetrates farther and farther into the soil with every year ofcultivation. For example, on a dry-farm, the soil of which is clay loam, and whichwas plowed in the fall of 1904 and farmed annually thereafter, the eighth foot containedin the spring of 1905, 6.59 per cent of moisture; in the spring of 1906, 13.11 percent, and in the spring of 1907, 14.75 per cent of moisture. On another farm, witha very sandy soil and also plowed in the fall of 1904, there was found in the eighthfoot in the spring of 1905, 5.63 per cent of moisture, in the spring of 1906, 11.41per cent of moisture, and in the spring of 1907, 15.49 per cent of moisture. In bothof these typical cases it is evident that as the topsoil was loosened, the full fieldwater capacity of the soil was more nearly approached to a greater depth. It wouldseem that, as the lower soil layers are moistened, the water is enabled, so to speak,to slide down more easily into the depths of the soil.

This is a very important principle for the dryfarmer to understand. It is always dangerous to permit the soil of a dry-farm tobecome very dry, especially below the first foot. Dry-farms should be so manipulatedthat even at the harvesting season a comparatively large quantity of water remainsin the soil to a depth of 8 feet or more. The larger the quantity of water in thesoil in the fall, the more readily and quickly will the water that falls on the landduring the resting period of fall, winter, and early spring sink into the soil andmove away from the topsoil. The top or first foot will always contain the largestpercentage of water because it is the chief receptacle of the water that falls asrain or snow but when the subsoil is properly moist, the water will more completelyleave the topsoil. Further, crops planted on a soil saturated with water to a depthof 8 feet are almost certain to mature and yield well.

If the field-water capacity has not been filled,there is always the danger that an unusually dry season or a series of hot windsor other like circumstances may either seriously injure the crop or cause a completefailure. The dry-farmer should keep a surplus of moisture in the soil to be carriedover from year to year, just as the wise business man maintains a sufficient workingcapital for the needs of his business. In fact, it is often safe to advise the prospectivedry-farmer to plow his newly cleared or broken land carefully and then to grow nocrop on it the first year, so that, when crop production begins, the soil will havestored in it an amount of water sufficient to carry a crop over periods of drouth.Especially in districts of very low rainfall is this practice to be recommended.In the Great Plains area, where the summer rains tempt the farmer to give less attentionto the soil-moisture problem than in the dry districts with winter precipitationfarther West, it is important that a fallow season be occasionally given the landto prevent the store of soil moisture from becoming dangerously low.


To what extent is the rainfall stored in soils?

What proportion of the actual amount of waterfalling upon the soil can be stored in the soil and carried over from season to season?This question naturally arises in view of the conclusion that water penetrates thesoil to considerable depths. There is comparatively little available informationwith which to answer this question, because the great majority of students of soilmoisture have concerned themselves wholly with the upper two, three, or four feetof soil. The results of such investigations are practically useless in answeringthis question. In humid regions it may be very satisfactory to confine soil-moistureinvestigations to the upper few feet; but in arid regions, where dry-farming is aliving question, such a method leads to erroneous or incomplete conclusions.

Since the average field capacity of soils forwater is about 2.5 inches per foot, it follows that it is possible to store 25 inchesof water in 10 feet of soil. This is from two to one and a half times one year'srainfall over the better dry-farming sections. Theoretically, therefore, there isno reason why the rainfall of one season or more could not be stored in the soil.Careful investigations have borne out this theory. Atkinson found, for example, atthe Montana Station, that soil, which to a depth of 9 feet contained 7.7 per centof moisture in the fall contained 11.5 per cent in the spring and, after carryingit through the summer by proper methods of cultivation, 11 per cent.

It may certainly be concluded from this experimentthat it is possible to carry over the soil moisture from season to season. The elaborateinvestigations at the Utah Station have demonstrated that the winter precipitation,that is, the precipitation that comes during the wettest period of the year, maybe retained in a large measure in the soil. Naturally, the amount of the naturalprecipitation accounted for in the upper eight feet will depend upon the drynessof the soil at the time the investigation commenced. If at the beginning of the wetseason the upper eight feet of soil are fairly well stored with moisture, the precipitationwill move down to even greater depths, beyond the reach of the soil auger. If, onthe other hand, the soil is comparatively dry at the beginning of the season, thenatural precipitation will distribute itself through the upper few feet, and thusbe readily measured by the soil auger.

In the Utah investigations it was found thatof the water which fell as rain and snow during the winter, as high as 95-1/2 percent was found stored in the first eight feet of soil at the beginning of the growingseason. Naturally, much smaller percentages were also found, but on an average, insoils somewhat dry at the beginning of the dry season, more than three fourths ofthe natural precipitation was found stored in the soil in the spring. The resultswere all obtained in a locality where the bulk of the precipitation comes in thewinter, yet similar results would undoubtedly be obtained where the precipitationoccurs mainly in the summer. The storage of water in the soil cannot be a whit lessimportant on the Great Plains than in the Great Basin. In fact, Burr has clearlydemonstrated for western Nebraska that over 50 per cent of the rainfall of the springand summer may be stored in the soil to the depth of six feet. Without question,some is stored also at greater depths.

All the evidence at hand shows that a large portionof the precipitation falling upon properly prepared soil, whether it be summer orwinter, is stored in the soil until evaporation is allowed to withdraw it Whetheror not water so stored may be made to remain in the soil throughout the season orthe year will be discussed in the next chapter. It must be said, however, that thepossibility of storing water in the soil, that is, making the water descend to relativelygreat soil depths away from the immediate and direct action of the sunshine and winds,is the most fundamental principle in successful dry-farming.


The fallow

It may be safely concluded that a large portionof the water that falls as rain or snow may be stored in the soil to considerabledepths (eight feet or more). However, the question remains, Is it possible to storethe rainfall of successive years in the soil for the use of one crop? In short, Doesthe practice of clean fallowing or resting the ground with proper cultivation forone season enable the farmer to store in the soil the larger portion of the rainfallof two years, to be used for one crop? It is unquestionably true, as will be shownlater, that clean fallowing or "summer tillage" is one of the oldest andsafest practices of dry-farming as practiced in the West, but it is not generallyunderstood why fallowing is desirable.

Considerable doubt has recently been cast uponthe doctrine that one of the beneficial effects of fallowing in dry-farming is tostore the rainfall of successive seasons in the soil for the use of one crop. Sinceit has been shown that a large proportion of the winter precipitation can be storedin the soil during the wet season, it merely becomes a question of the possibilityof preventing the evaporation of this water during the drier season. As will be shownin the next chapter, this can well be effected by proper cultivation.

There is no good reason, therefore, for believingthat the precipitation of successive seasons may not be added to water already storedin the soil. King has shown that fallowing the soil one year carried over per squarefoot, in the upper four feet, 9.38 pounds of water more than was found in a croppedsoil in a parallel experiment; and, moreover, the beneficial effect of this. wateradvantage was felt for a whole succeeding season. King concludes, therefore, thatone of the advantages of fallowing is to increase the moisture content of the soil.The Utah experiments show that the tendency of fallowing is always to increase thesoil-moisture content. In dry-farming, water is the critical factor, and any practicethat helps to conserve water should be adopted. For that reason, fallowing, whichgathers soil-moisture, should be strongly advocated. In Chapter IX another importantvalue of the fallow will be discussed.

In view of the discussion in this chapter itis easily understood why students of soil-moisture have not found a material increasein soil-moisture due to fallowing. Usually such investigations have been made toshallow depths which already were fairly well filled with moisture. Water fallingupon such soils would sink beyond the depth reached by the soil augers, and it becameimpossible to judge accurately of the moisture-storing advantage of the fallow. Acritical analysis of the literature on this subject will reveal the weakness of mostexperiments in this respect.

It may be mentioned here that the only fallowthat should be practiced by the dry-farmer is the clean fallow. Water storage ismanifestly impossible when crops are growing upon a soil. A healthy crop of sagebrush,sunflowers, or other weeds consumes as much water as a first-class stand of corn,wheat, or potatoes. Weeds should be abhorred by the farmer. A weedy fallow is a sureforerunner of a crop failure. How to maintain a good fallow is discussed in ChapterVIII, under the head of Cultivation. Moreover, the practice of fallowing should bevaried with the climatic conditions. In districts of low rainfall, 10-15 inches,the land should be clean summer-fallowed every other year; under very low rainfallperhaps even two out of three years; in districts of more abundant rainfall, 15-20inches, perhaps one year out of every three or four is sufficient. Where the precipitationcomes during the growing season, as in the Great Plains area, fallowing for the storageof water is less important than where the major part of the rainfall comes duringthe fall and winter. However, any system of dry-farming that omits fallowing whollyfrom its practices is in danger of failure in dry years.


Deep plowing for water storage

It has been attempted in this chapter to demonstratethat water falling upon a soil may descend to great depths, and may be stored inthe soil from year to year, subject to the needs of the crop that may be planted.By what cultural treatment may this downward descent of the water be acceleratedby the farmer? First and foremost, by plowing at the right time and to the rightdepth. Plowing should be done deeply and thoroughly so that the falling water mayimmediately be drawn down to the full depth of the loose, spongy, plowed soil, awayfrom the action of the sunshine or winds. The moisture thus caught will slowly workits way down into the lower layers of the soil. Deep plowing is always to be recommendedfor successful dry-farming.

In humid districts where there is a great differencebetween the soil and the subsoil, it is often dangerous to turn up the lifeless subsoil,but in arid districts where there is no real differentiation between the soil andthe subsoil, deep plowing may safely be recommended. True, occasionally, soils arefound in the dry-farm territory which are underlaid near the surface by an inertclay or infertile layer of lime or gypsum which forbids the farmer putting the plowtoo deeply into the soil. Such soils, however' are seldom worth while trying fordry-farm purposes. Deep plowing must be practiced for the best dry-farming results.

It naturally follows that subsoiling should bea beneficial practice on dry-farms. Whether or not the great cost of subsoiling isoffset by the resulting increased yields is an open question; it is, in fact, quitedoubtful. Deep plowing done at the right time and frequently enough is possibly sufficient.By deep plowing is meant stirring or turning the soil to a depth of six to ten inchesbelow the surface of the land.


Fall plowing far water storage

It is not alone sufficient to plow and to plowdeeply; it is also necessary that the plowing be done at the right time. In the verygreat majority of cases over the whole dry-farm territory, plowing should be donein the fall. There are three reasons for this: First, after the crop is harvested,the soil should be stirred immediately, so that it can be exposed to the full actionof the weathering agencies, whether the winters be open or closed. If for any reasonplowing cannot be done early it is often advantageous to follow the harvester witha disk and to plow later when convenient. The chemical effect on the soil resultingfrom the weathering, made possible by fall plowing, as will be shown in Chapter IX,is of itself so great as to warrant the teaching of the general practice of fallplowing. Secondly, the early stirring of the soil prevents evaporation of the moisturein the soil during late summer and the fall. Thirdly, in the parts of the dry-farmterritory where much precipitation occurs in the fall, winter, or early spring, fallplowing permits much of this precipitation to enter the soil and be stored thereuntil needed by plants.

A number of experiment stations have comparedplowing done in the early fall with plowing done late in the fall or in the spring,and with almost no exception it has been found that early fall plowing is water-conservingand in other ways advantageous. It was observed on a Utah dry-farm that the fall-plowedland contained, to a depth of 10 feet, 7.47 acre-inches more water than the adjoiningspring-plowed land--a saving of nearly one half of a year's precipitation. The groundshould be plowed in the early fall as soon as possible after the crop is harvested.It should then be left in the rough throughout the winter, so that it may be mellowedand broken down by the elements. The rough lend further has a tendency to catch andhold the snow that may be blown by the wind, thus insuring a more even distributionof the water from the melting snow.

A common objection to fall plowing is that theground is so dry in the fall that it does not plow up well, and that the great dryclods of earth do much to injure the physical condition of the soil. It is very doubtfulif such an objection is generally valid, especially if the soil is so cropped asto leave a fair margin of moisture in the soil at harvest time. The atmospheric agencieswill usually break down the clods, and the physical result of the treatment willbe beneficial. Undoubtedly, the fall plowing of dry land is somewhat difficult, butthe good results more than pay the farmer for his trouble. Late fall plowing, afterthe fall rains have softened the land, is preferable to spring plowing. If for anyreason the farmer feels that he must practice spring plowing, he should do it asearly as possible in the spring. Of course, it is inadvisable to plow the soil whenit is so wet as to injure its tilth seriously, but as soon as that danger periodhas passed, the plow should be placed in the ground. The moisture in the soil willthereby be conserved, and whatever water may fall during the spring months will beconserved also. This is of especial importance in the Great Plains region and inany district where the precipitation comes in the spring and winter months.

Likewise, after fall plowing, the land must bewell stirred in the early spring with the disk harrow or a similar implement, toenable the spring rains to enter the soil easily and to prevent the evaporation ofthe water already stored. Where the rainfall is quite abundant and the plowed landhas been beaten down by the frequent rains, the land should be plowed again in thespring. Where such conditions do not exist, the treatment of the soil with the diskand harrow in the spring is usually sufficient.

In recent dry-farm experience it has been fairlycompletely demonstrated that, providing the soil is well stored with water, cropswill mature even if no rain falls during the growing season. Naturally, under mostcircumstances, any rains that may fall on a well-prepared soil during the seasonof crop growth will tend to increase the crop yield, but some profitable yield isassured, in spite of the season, if the soil is well stored with water at seed time.This is an important principle in the system of dry-farming.