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CHAPTER XVIII

SOIL WATER: HOW IT IS LOST; HOW IT MAY BE HELD

The operation of loosening and stirring the soil usually is spoken of as tillage or cultivation. Heretofore four reasons have been advanced in support of tillage: it increases the root room for the plant; it admits air into the soil so that plant food may be more readily prepared; it secures oxygen for plant roots; and it destroys weeds.

[graphic]

THE RESULT WHEN WATER IS SECURED AND HELD

The annual rainfall where these sugar beets were grown was but 20 inches

We must not overlook two other tillage operations that stand out prominently in any rational treatment of the soil. These are: the rainfall is enabled to enter the soil easily; the loss of water by evaporation is checked.

While each of these operations deserves careful attention, the last two are open to more gentle treatment and to more sensitive consideration than the operations previously described.

Transpiration: the exit through the leaves. We have learned that roots gather moisture and carry it into the

plant. This moisture, or water, conveys the soil nutriment with it to the plants. It then passes on up through the stems and leaves, to be exhaled, finally, through the leaves. The loss of water to the soil, by this means, is very large. For ordinary crops, from 300 to 500 pounds. of water are required to produce one pound of dry matter.

[graphic]

EFFECT OF CULTIVATION OF CORN CROP

Plot at right received ordinary good cultivation, and yielded 64 bushels of corn Plot at left received no cultivation, and yielded 4 bushels of corn

per acre. per acre

It has been estimated that for average production of some common crops, the amount of water required for producing a single acre is as follows: Clover, 400 tons; corn, 350 tons; grapes, 375 tons; oats, 375 tons; potatoes, 450 tons; wheat, 350 tons; and peas, 375 tons.

As the rainfall during the growing season is not sufficient as a means of supplying water to the crop, the water stored in the soil must be drawn upon considerably. This fact lays stress upon the importance of large water supplies in the soil, not as stagnant water, but as capillary

water, closely identified with soil grains. It should be remembered that drainage applies to lands only that are flat or naturally wet, and then mainly in the early part of the season, while the saving of moisture is the main factor in most soils.

Evaporation: drying out by sun and wind.-A second source of water loss is due to the action of the sun and wind, which cause water vapor to rise directly from the

[graphic][merged small]

We cultivate to kill weeds, to conserve the moisture in the soil, and to render plant food available

surface of the soil. It matters not how much or how little moisture there is present in the soil; just the same, there is a constant loss, and notably so if the atmosphere is hot or dry. This escape of moisture is of prime importance to every farmer. It is needed in the soil; particularly is this true in dry seasons and during the summer months.

While it is true that every soil has a reserve store of water, it is just as true that this reserve supply often gets low, and especially is this so when the weather is hot

and dry. Capillarity causes the trouble. We suppose that capillarity is an agent at work bringing water from lower depths up to roots for our good, only; but let us remember that this same force carries water higher than the root region, merely; it carries it up to the very top, where, when in contact with the surface, it is licked up by winds and atmosphere, and borne away beyond reach of soil or plant or man.

Cultivation checks evaporation.-It now becomes manifest that soils must be cultivated, not only to make them wholesome and attractive to seeds, and to kill weeds, but to cultivate them, also, to conserve this moisture-to check the loss occasioned by evaporation.

Naturally, a question arises: Does cultivation conserve moisture in the soil? In answer to this, let us consult the soil about the matter. In New Hampshire the observed differences between two plots are given below:

[blocks in formation]

Here is a saving of 352.64 tons of water per acre on the cultivated plot. Certainly, a saving of tremendous bearing during seasons of dry weather.

Water must be carried into the soil.-As a preliminary step in conserving soil moisture, water must be admitted to the soil. And right here is one of the spots where it is well to give close attention: you must get water into the soil before you can save it. Often the supply is short, and

the least bit wasted acts as a handicap for the coming crop. Good farm practice aims to have and to hold the surface of the soil in such condition that the whole of the rain supply shall be received into it, and by gravitation drawn to the lower regions where the water stores are held and preserved.

Whenever the surface of the soil is tight and stiff and impervious, you may be sure that a good part of every rain will never get into the soil, but will be lost by surface drainage. And you must aim to get the rains of the entire year; not those that come during the growing season, only, but those of fall and winter and early spring, as well. Often the summer rains fall far short of the plants' demands, even though they are utilized in their entirety. Good crops often are produced when the rainfall, during the period of growth, is no more than a quarter of the quantity demanded and used by the plant. This is possible solely for the reason that there has been got into the soil a large part of the water that fell as rain earlier in the season-during the fall and winter months.

It is not stating the facts too loosely to say that in humid regions as much as 25 per cent. of the entire rainfall is lost to the soil, and for this reason: The streams get it, because the surface crust acts so slowly in absorbing the waters that come to it, the real amount obtained being much less than what it ought to be. And the same fault is applicable to semi-arid regions. While the loss here is not so great, it is only because the rainfall is less and the land more level and attractive to rain. A loss in this way of 10 per cent.—a most conservative estimatemeans much, considering the fact that the average rainfall is but twenty inches annually.

It will be worth your while to remember that the water that runs off of the surface is not only lost to plants, but

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