We must underdrain all the land we cultivate, that Nature has not already underdrained, and we shall cease complaints of the seasons. The advice of Cromwell to his soldiers: "Trust God, and keep your powder dry," affords a good lesson of faith and works to the farmer. We shall seldom have a season, upon properly drained land, that is too wet, or too cold, or even too dry; for thorough draining is almost as sure a remedy for a drought, as for a flood.
Do lands need under draining in America? It is a common error to suppose that, because the sun shines more brightly upon this country than upon England, and because almost every Summer brings such a drought here as is unknown there, her system of thorough drainage can have no place in agriculture on this side of the Atlantic. It is true that we have a clearer sky and a drier climate than are experienced in England; but it is also true that, although we have a far less number of showers and of rainy days, we have a greater quantity of rain in the year.
The necessity of drainage, however, does not depend so much upon the quantity of water which falls or flows upon land, nor upon the power of the sun to carry it off by evaporation, as upon the character of the subsoil. The vast quantity of water which Nature pours upon every acre of soil annually, were it all to be removed by evaporation alone, would render the whole country barren; but Nature herself has kindly done the work of draining upon a large proportion of our land, so that only a healthful proportion of the water which falls on the earth, passes off at the surface by the influence of the sun.
If the subsoil is of sand or gravel, or of other porous earth, that portion of the water not evaporated, passes off below by natural drainage. If the subsoil be of clay, rock, or other impervious substances, the downward course of the water is checked, and it remains stagnant, or bursts out upon the surface in the form of springs.
As the primary object of drainage is to remove surplus water, it may be well to consider with some care
THE SOURCES OF MOISTURE.
Springs.—These are, as has been suggested, merely the water of rain and snow, impeded in its downward percolation, and collected and poured forth in a perennial flow at a lower level.
The water which falls in the form of rain and snow upon the soil of the whole territory of the United States, east of the Rocky Mountains, each year, is sufficient to cover it to the depth of more than 3 feet. It comes upon the earth, not daily in gentle dews to water the plants, but at long, unequal intervals, often in storms, tempests, and showers, pouring out, sometimes, in a single day, more than usually falls in a whole month.
What becomes of all this moisture, is an inquiry especially interesting to the agriculturist, upon whose fruitful fields this flood of water annually descends, and whose labor in seed-time would be destroyed by a single Summer shower, were not Nature more thoughtful than he, of his welfare. Of the water which thus falls upon cultivated fields, a part runs away into the streams, either upon the surface, or by percolation through the soil; a part is taken up into the air by evaporation, while a very small proportion enters into the constitution of vegetation. The proportion which passes off by percolation varies according to the nature of the soil in the locality where it falls.
Usually, we find the crust of the earth in our cultivated fields, in strata, or layers: first, a surface-soil of a few inches of a loamy nature, in which clay or sand predominates; and then, it may be, a layer of sand or gravel, freely admitting the passage of water; and, perhaps, next, and within two or three feet of the surface, a stratum of clay, or of sand or gravel cemented with some oxyd of iron, through which water passes very slowly, or not at all. These strata are sometimes regular, extending at an equal depth over large tracts, and having a uniform dip, or inclination. Oftener, however, in hilly regions especially, they are quite irregular—the impervious stratum frequently having depressions of greater or less extent, and holding water, like a bowl. Not unfrequently, as we cut a ditch upon a declivity, we find that the dip of the strata below has no correspondence with the visible surface of the field, but that the different strata lie nearly level, or are much broken, while the surface has a regular inclination.