CHAPTER V.

ADVANTAGES OF DRAINING RETENTIVE SOILS.

As there are many farms that do not need draining, it may be well to inquire under what conditions it can be profitably practiced. It would certainly be a foolish expenditure of money and labor, to lay drains in land that has a permeable subsoil and allows the free percolation of hydrostatic water, so that the water table is at least four feet below the surface in wet seasons, or after heavy rains. There are extensive tracts of open, porous soils that are not fertile from lack of power to retain capillary water in sufficient quantity to support vegetation, in which irrigation rather than draining is indicated.

Draining can only be recommended when there is a retentive subsoil, which holds the drainage water for a considerable time in the spring and fall months, or after a heavy rainfall in the growing season. It will at once be admitted that swamps and bogs that are saturated with water for several months in the year, and lands overflowed by springs, need draining, but on high lands there are less obvious indications of deficient drainage, which the intelligent observer will not fail to notice.

Indications that High Lands Need Draining. Where water stands on the surface after heavy showers, or is seen in the furrows when plowing in the spring, the soil will, undoubtedly, be improved by draining. Even where water does not show itself at the surface, the dark patches of soil in a recently plowed field, and the growth of mosses, or molds, and aquatic plants, later in the season, show that the water table must be lowered

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to provide favorable conditions for the growth of upland plants of greater economic value. The accumulation of water in trial pits, that may be dug to the depth of three or four feet, in wet seasons, is another indication that is quite conclusive.

The indications of deficient drainage are likewise manifest in time of drouth, among which may be mentioned, as the most striking, the appearance of wide cracks in heavy soils that have been saturated with water early in the season, and then dried by evaporation. In such soils there is a lack of porosity, or capillarity; the roots of plants are not well developed, from the absence of suitable conditions for their distribution throughout the soil, and the rolling of the leaves indicates a deficient supply of capillary water for healthy nutrition. After copious showers the plants frequently have a yellowish tinge, from defective assimilation arising from the presence of hydrostatic water in the soil, and at the close of the season the crop matures, or ripens unevenly in the field. Soil metabolism is not active; the conditions do not favor the free circulation of capillary water in the soil, or vigorous root development, and the crop suffers from the check given to its general processes of nutrition. In contrast with these unfavorable conditions for growing crops, we may summarize some of the benefits that may be derived from a judicious system of farm drainage.

Advantages of Draining Retentive Soils. As the surface of the water table is the limit of the healthy root development of farm crops, one of the most obvious effects of draining is to deepen the soil, and thus furnish a wider range for these important agents of nutrition and growth. If the water table is within four feet of the surface of the soil for any considerable time during the growing season, it must materially interfere with the development and distribution of the roots of

most of our farm crops, as, under favorable conditions, they penetrate the soil to greater depths than the limit mentioned, which may be considered the minimum for profitable production.

Schubert made excavations in the field six feet, or more, in depth, and then laid bare the roots of plants by gently washing the soil with a stream of water. He found that rye, beans and garden peas had a dense mat of fine fibrous roots to a depth of four feet from the surface, and wheat roots were traced to the depth of seven feet forty-seven days after sowing, while other crops had roots ranging to the depth of three or four feet.* A greater range of root development has frequently been reported by other observers.

There are numerous indirect advantages of thorough draining which should not be overlooked. On well drained land the rain falling upon the soil, in excess of its capacity for absorption, or the demands of the crop, percolates downwards to the level of the drains, warming the soil in its progress, and increasing its porosity, while the air follows the descending water between the particles of the soil, where its constituents are needed for the nutrition of the plants, and in the processes of soil metabolism. Next to carbon we find oxygen is the most abundant element in the composition of plants. It is freely absorbed by the roots of plants, and "“deprived of oxygen the movements of protoplasm, the movements of the roots and of the leaves cease, other manifestations of activity are put a stop to, and the plant dies of suffocation." Atmospheric nitrogen, also, as we have seen, is appropriated by micro-organisms in the soil, and made available as combined nitrogen for the use of plants. The free admission of the atmosphere between the particles of soils is, therefore, important, and this can only be secured on well drained land.

*How Crops Grow, p. 264.

† Plant Life on the Farm, p. 25.

When the hydrostatic water of soils is discharged by drainage, instead of evaporation, there is an immense saving of energy in the form of heat, as has been pointed out in a preceding chapter (p. 63), that may be made available for other purposes, of direct advantage to the growing crops. The enormous amount of heat saved from useless work by drainage would be utilized in warming the soil, and in the metabolic processes that are essential to the healthy, luxuriant growth of crops. Soil metabolism would be promoted, the micro-organisms concerned in the disintegration of organic matters in the soil, and, in the processes of nitrification, would find more favorable conditions for the exercise of their vital activities, plant food would be more rapidly elaborated, and the power of the soil to hold water by capillary attraction in the form best suited for the use of growing plants, would be materially increased.

enhanced porosity of the soil would not only favor beneficial metabolic activities in the soil itself, but, from the improved biological conditions, the roots of plants would be more widely distributed, as they could readily penetrate the soil in all directions, so that its entire mass would be utilized.

Heavy soils, when saturated with water, are injured by working, or by the treading of cattle, as the process of "puddling," as it is technically called, takes place and renders them more retentive and compact. When the water absorbed by such soils is removed by evaporation they become hard and tough, and they do not readily absorb water again, or allow it to percolate through them. In drying they shrink and crack, to the injury of the feeble roots that may have been formed near the surface. They are difficult to work, from their tenacity, and are not easily pulverized, so that thorough tillage, or the preparation of a good seed bed, is made impracticable. These "heavy" soils weigh least,

The sum of the ameliorating effects of draining such soils is to lengthen the season, as they can then be worked earlier in the spring and later in the fall, plants have a longer period of active growth, and a thorough preparation of the soil for seeding can be secured, with economy and increased efficiency in the labor expended.

Among the incidental advantages of draining we should not omit to notice that the surface soil is not washed by heavy rains; and water furrows, that interfere with cultivation and the use of harvesting machinery, may be dispensed with; that crops are not injured by the heaving of the soil by frost; that they are of better quality, and ripen evenly, which is an important consideration in harvesting. It is only on well drained land that manures produce their full effect, either as supplies of plant food, or through their indirect action of increasing soil metabolism.

There are retentive, undrained soils, which yield fair crops in the exceptional seasons, that furnish the most favorable conditions of temperature and distribution of rainfall for their special requirements, while in bad seasons the total failure of the crop, or the decidedly low yield in ordinary seasons, tends to reduce the average below the point of profitable production.

Drainage and Drouths. In localities where the average annual rainfall considerably exceeds the amount required by crops, drouths are liable to occur from an unequal distribution of rain throughout the year, and an absolute deficiency in the growing season. The influence of drainage in promoting the growth of crops in time of drouth should, therefore, receive particular attention.

On well drained land, of fair quality, plants have a vigorous habit of growth that enables them to resist, or overcome, to a certain extent, the injurious influences which, under less favorable conditions, would be mani