Dry-Farming

In dry-farm districts such loss is a rare occurrence, for the natural precipitation is not sufficiently large to connect with the country drainage, and it may, therefore, be eliminated from

is, in districts where dry-farming is properly carried on, very much larger than that resulting either from seepage or from direct evaporation. While plants are growing, evaporation from plants, ordinarily called transpiration, continues. Experiments performed in various arid districts have shown that one and a half to three times more water evaporates f

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uence in water absorption. All parts of the roots do not possess equal power of taking up soil-water. In the process of water absorption the younger roots are most active and effective. Even of the young roots, however, only certain parts are actively engaged in water absorption. At the very tips of the young growing roots are numerous fine hairs. These root-hairs, which cluster about the growing point of the young roots, are the organs of the plant that absorb soil-water. They are of value only for lim

solution within the root-hair is of different degree from the soil-water solution. The water tends, therefore, to move from the soil into the root, in order to make the solutions inside and outside of the root of the same concentration. If it should ever occur that the soil-water and the water within the root-hair became the same concentration, that is to say, contained the same s

one of them is absent, it is absolutely impossible for the plant to continue its life functions. The indispensable plant-foods gathered from the soil by the root-hairs, in addition to water, are: potassium, calcium, magnesium, iron, nitrogen, and phosphorus,-all in their proper combinations. How the plant uses these substa

nished in their content of particular plant-foods, more enters from the soil solution. The necessary plant-foods do not alone enter the plant but whatever may be in solution in the soil-water enters the plant in variable quantities. Nevertheless, since the plant uses only a few definite substances and leaves the unnecessar

f water th

ell, but moves through tubes that apparently have been formed for the specific purpose of aiding the movement of water through the plant. The rapidity of this current is often considerable. Ordinarily, it varies from one foot to six feet per hour, though observ

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mbined with the carbon and these mineral substances to form the characteristic products of plant life. The carbon which forms over half of the plant substance is gathered from the air by the leaves and it is evident that the leaves are very active agents of plant growth. The atmosphere consists chiefly of the gases oxygen and nitrogen in the proportion of one to four, but associated with them are small quantities of various other substances. Chief among the secondary constituents of the atmosphere is the gas carbon d

the upper side of plants. In fact, there is often five times more on the under side than on the upper side of a leaf. It has been estimated that 150,000 stomata or more are often found per square inch on the under side of the leaves of ordinary cultivated plants. The stomata or breathing-pores are so constructed t

of plants, but it is seldom more than a thirtieth or a fortieth of the total transpiration. The evaporation of water from the leaves through the breathing-pores is the so-called transpiration, wh

spir

es of the absorption of water from the soil. As evaporation is diminished the amount of water that enters the plants is also diminished. Yet transpiration appears to be a process wholly necessary for plant life. The question is, simply, to what extent it may be diminishe

wholly stopped for even a few hours, the plant is likely to be so

ssimilation of the carbon by the leaves; thirdly, because it is not unlikely that the heat required to evaporate water, in large part taken from the plant itself, prevents the plant from being overheated. This last mentioned value of t

nfluencing t

full powers. That the evaporation of water from the soil or from a free water surface is not the same as that from plant leaves may be shown in a general way from the fact that the amount of water transpired from a given area of leaf surface may be very much larger or very much smaller than that evaporated from an equal surface of free wate

uencing the transpiration m

from a free water surface, the transpiration of plants still continues in a small degree. This is explained by the observation that since the life process of a plant produces a certain amount of heat, the plant is always warmer than the surrounding air and

tions otherwise the same, transpiration is more rapid on a warm day than on a cold one

air currents, which is to say, that on a windy day t

ity, temperature, and wind, transpiration is reduced to a minimum during the night and increases manyfold during the day when direct sunlight

of large quantities of the substances which the plant needs for its

ome effect upon the transpiration. At times it is increased

Just before blooming it is very much larger and in time of bloom it is the largest in the history of the p

in the reclamation of dry-farm districts. Moreover, the same crop grown under different conditions varies in its rate of transpiration. For instance, plants grown for some time under arid conditions greatly modify their rate of transpiration, as shown by Spalding, who reports that a plant reared under humid conditions gave off 3.7 times as much water as the same plant reared under arid conditions. This very interesting observation tends to confirm the view commonly h

s, the more rapidly does it transpire water, for it is well known that the most luxuriant plant growth occurs in the tropics, where the transpiration is ex

rate of transpiration. The more vigorous and extensive the root sys

ted that the subject of transpiration is yet poorly understood, though it is one of the most important subjects in its applications to plant production in localities where water is scaree. It should also be noted that

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the amount of water transpired by the plant in the comparatively pure rain water was nearly 20 per cent higher than that used by the plant growing in the notoriously impure water of the River Thames. Sachs, in 1859, carried on an elaborate series of experiments on transpiration in which he showed that the addition of potassium nitrate, ammonium sulphate or common salt to the solution in which plants grew reduced the transpiration; in fact, the reduction was large, varying from 10 to 75 per cent. This was confirmed by a number of later workers, among them, for instance, Buergerstein, who, in

ction in transpiration; if they are added to the soil on which plants are growing, the same effect will result. The addition of commercial fertilizers to the soil will therefore diminish transpiration. It was further discovered nearly half a century ago that similar plants growing on different soils evaporate different amounts of water from their leaves; this difference, undoubt

for a pound

study of transpiration. If varying the transpiration varies the growth, there would be no special advantage in reducing the transpiration. From an economic point of view the important question is this: Doe

down the law that poor plant nutrition increases the water-cost of every pound of dry matter produced. It was about this time that the Rothamsted Experiment Station reported that its experiments had shown that during periods of drouth the well-tilled and well-fertilized fields yielded good crops, while the unfertilized fields yielded poor crops or crop failures-indicating thereby, since rainfall was the critical factor, that the fertility of the soil is important in determining whether or not with a small amount of water a good crop can be produced. Pagnoul, working in 1895 with fescue grass, arrived at the same conclusion. On a poor clay soil it required 1109 pounds of water to produce one pound of dry matter, while on a rich calcareous soil only 574 pounds were required. Gardner of the United States Department of Agriculture, Bureau of Soils, working in 1908, on the manuring of soils, came to the conclusion that the more fertile the soil the less water is required to produce a pound of dry matter. He incidentally called attention to the fact that in countries of limited rainfall this might be a very important principle to apply in crop production. Hopkins in his study of the soils of Illinois has repeatedly observed, in connection with certai

ontrolling t

s in reducing the amount of water required by plants. The experiments at the Utah Station, already referred to, bring out very strikingly the value of cultivation in reducing the transpiration. For instance, in a series of experiments the following results were obtained. On a sandy loam, not cultivated, 603 pounds of water were transpired to produce one pound of dry matter of corn; on the same soil, cultivated, only 252 pounds were required. On a clay loam, not cultivated, 535 pounds of water were transpired for each pound of dry matter, whereas on the cultivated soil only 428 pounds were necessary. On a clay soil, not cultivated, 753 pounds of water were transpired for each pound of dry matter; on the cultivated soil, only 582 pounds. The farm

r each pound of dry matter. For the clay 7466 pounds on the cropped part and 1739 pounds on the previously bare part were required for each pound of dry matter. These results teach clearly and emphatically that the fertile condition of the soil induced by fallowing makes it possible to produce dry matter with a smaller amount of water than can be done on soils that are cropped continuously. The beneficial effects of fallowing are therefore clearly twofold: to store the moisture of two seasons for the use of one crop; and to set free fertility to enable the plant to grow with the least amount of water. It is not yet fully understood what changes occur in fallowing to give the soil the fertility which reduces the water needs of the plant. The researches of Atkinson in Montana, Stewart and Graves in Utah, and Jensen in South Dakota ma

elow the surface by the plant roots. When this stubble is plowed under there is a valuable addition of the plant-food to the upper soil. Further, as the stubble decays, acid substances are produced that act upon the soil grains to set free the plant-food locked up in them. The plowing un

orating directly from the soil; but the soil must be kept in such a state of high fertility that plants are enabled to utilize the stored moisture in the most economical manne