Farm drainage Part 4

RAIN, EVAPORATION, AND FILTRATION.

Fertilizing Substances in Rain Water.--Amount of Rain Fall in United States--in England.--Tables of Rain Fall.--Number of Rainy Days, and Quant.i.ty of Rain each Month.--Snow, how Computed as Water.--Proportion of Rain Evaporated.--What Quant.i.ty of Water Dry Soil will Hold.--Dew Point.--How Evaporation Cools Bodies.--Artificial Heat Underground.--Tables of Filtration and Evaporation.

Although we usually regard drainage as a means of rendering land sufficiently dry for cultivation, that is by no means a comprehensive view of the objects of the operation.

Rain is the princ.i.p.al source of moisture, and a surplus of moisture is the evil against which we contend in draining. But rain is also a princ.i.p.al source of fertility, not only because it affords the necessary moisture to dissolve the elements of fertility already in the soil, but also because it contains in itself, or brings with it from the atmosphere, valuable fertilizing substances. In a learned article by Mr.

Caird, in the Cyclopedia of Agriculture, on the Rotation of Crops, he says:

"The surprising effects of a fallow, even when unaided by any manure, has received some explanation by the recent discovery of Mr. Barral, that rain-water contains within itself, and conveys into the soil, fertilizing substances of the utmost importance, equivalent, in a fall of rain of 24 inches per annum, to the quant.i.ty of ammonia contained in 2 cwt. of Peruvian guano, with 150 lbs. of nitrogeneous matter besides, all suited to the nutrition of our crops."

About 42 inches of rain may be taken as a fair general average of the rain-fall in the United States. If this supplies as much ammonia to the soil as 3 cwt. of Peruvian guano to the acre, which is considered a liberal manuring, and which is valuable princ.i.p.ally for its ammonia, we at once see the importance of retaining the rain-water long enough upon our fields, at least, to rob it of its treasures. But rain-water has a farther value than has yet been suggested:

"Rain-water always contains in solution, air, carbonic acid, and ammonia. The two first ingredients are among the most powerful disintegrators of a soil. The oxygen of the air, and the carbonic acid being both in a highly condensed form, by being dissolved, possess very powerful affinities for the ingredients of the soil.

The oxygen attacks and oxydizes the iron; the carbonic acid seizing the lime and potash and other alkaline ingredients of the soil, produces a further disintegration, and renders available the locked-up ingredients of this magazine of nutriment. Before these can be used by plants, they must be rendered soluble; and this is only affected by the free and renewed access of rain and air. The ready pa.s.sage of both of these, therefore, enables the soil to yield up its concealed nutriment."

We see, then, that the rains of heaven bring us not only water, but food for our plants, and that, while we would remove by proper drainage the surplus moisture, we should take care to first conduct it through the soil far enough to fulfill its mission of fertility. We cannot suppose that all rain-water brings to our fields precisely the same proportion of the elements of fertility, because the foreign properties with which it is charged, must continually vary with the condition of the atmosphere through which it falls, whether it be the thick and murky cloud which overhangs the coal-burning city, or the transparent ether of the mountain tops. We may see, too, by the tables, that the quant.i.ty of rain that falls, varies much, not only with the varying seasons of the year, and with the different seasons of different years, but with the distance from the equator, the diversity of mountain and river, and lake and wood, and especially with locality as to the ocean. Yet the average results of nature's operations through a series of years, are startlingly constant and uniform, and we may deduce from tables of rain-falls, as from bills of mortality and tables of longevity, conclusions almost as reliable as from mathematical premises.

The quant.i.ty of rain is generally increased by the locality of mountain ranges. "Thus, at the Edinburgh Water Company's works, on the Pentland Hills, there fell in 1849, nearly twice as much rain as at Edinburgh, although the distance between the two places is only seven miles."

Although a much greater quant.i.ty of rain falls in mountainous districts (within certain limits of elevation) than in the plains, yet a greater quant.i.ty of rain falls at the surface of the ground than at an elevation of a few hundred feet. Thus, from experiments which were carefully made at York, it was ascertained that there fell eight and a half inches more rain at the surface of the ground, in the course of twelve months, than at the top of the Minster, which is 212 feet high. Similar results have been obtained in many other places.

Some observations upon this point may also be found in the Report of the Smithsonian Inst.i.tution for 1855, at p. 210, given by Professor C. W.

Morris, of New York.

Again, the evaporation from the surface of water being much greater than from the land, clouds that are wafted by the winds from the sea to the land, condense their vapor upon the colder hills and mountain sides, and yield rain, so that high lands near the sea or other large bodies of water, from which the winds generally blow, have a greater proportion of rainy days and a greater fall of rain than lands more remote from water.

The annual rain-fall in the lake districts in c.u.mberland County, in England, sometimes amounts to more than 150 inches.

With a desire to contribute as much as possible to the stock of accurate knowledge on this subject, we availed ourselves of the kindly offered services of our friends, Shedd and Edson, in preparing a carefully considered article upon a part of our general subject, which has much engaged their attention. Neither the article itself, nor the observations of Dr. Hobbs, which form a part of its basis, has ever before been published, and we believe our pages cannot be better occupied than by giving them in the language of our friends:

"All vegetables, in the various stages of growth, require warmth, air, and moisture, to support life and health.

Below the surface of the ground there is a body of stagnant water, sometimes at a great depth, but in retentive soils usually within a foot or two of the surface. This stagnant water not only excludes the air, but renders the soil much colder, and, being in itself of no benefit, without warmth and air, its removal to a greater depth is very desirable.

A knowledge of the depth to which this water-table should be removed, and of the means of removing it, const.i.tutes the science of draining, and in its discussion, a knowledge of the rain-fall, humidity of the atmosphere, and amount of evaporation, is very important.

The amount of rain-fall, as shown by the hyetal, or rain-chart, of North America, by Lorin Blodget, is thirty inches vertical depth in the basin of the great lakes; thirty-two inches on Lake Erie and Lake Champlain; thirty-six inches in the valley of the Hudson, on the head waters of the Ohio, through the middle portions of Pennsylvania and Virginia, and western portion of North Carolina; forty inches in the extreme eastern and the northern portion of Maine, northern portions of New Hampshire and Vermont, south-eastern counties of Ma.s.sachusetts, Central New York, north-east portion of Pennsylvania, south-east portion of New Jersey and Delaware; also, on a narrow belt running down from the western portion of Maryland, through Virginia and North Carolina, to the north-western portion of South Carolina; thence, up through the western portion of Virginia, north-east portion of Ohio, Northern Indiana and Illinois, to Prairie du Chien; forty-two inches on the east coast of Maine, Eastern Ma.s.sachusetts, Rhode Island, and Connecticut, and middle portion of Maryland; thence, on a narrow belt to South Carolina; thence, up through Eastern Tennessee, through Central Ohio, Indiana, and Illinois, to Iowa; thence, down through Western Missouri and Texas to the Gulf of Mexico; forty-five inches from Concord, New Hampshire, through Worcester, Ma.s.s., Western Connecticut, and the City of New York, to the Susquehanna River, just north of Maryland; also, at Richmond, Va., Raleigh, N. C., Augusta, Geo., Knoxville, Tenn., Indianopolis, Ind., Springfield, Ill., St.

Louis, Mo.; thence, through Western Arkansas, across Red River to the Gulf of Mexico. From the belt just described, the rain-fall increases inland and southward, until at Mobile, Ala., the rain-fall is sixty-three inches. The same amount also falls in the extreme southern portion of Florida.

In England, the average rain-fall in the eastern portion is represented at twenty inches; in the middle portion, twenty-two inches; in the southern and western, thirty inches; in the extreme south-western, forty-five inches; and in Wales, fifty inches. In the eastern portion of Ireland, it is twenty-five inches; and in the western, forty inches.

Observations at London for forty years, by Dalton, gave average fall of 20.69 inches. Observations at New Bedford, Ma.s.s., for forty-three years, by S. Rodman, gave average fall of 41.03 inches--about double the amount in London. The mean quant.i.ty for each month, at both places, is as follows:

_New Bedford._ _London._

January 3.36 1.46 February 3.32 1.25 March 3.44 1.17 April 3.60 1.28 May 3.63 1.64 June 2.71 1.74 July 2.86 2.45 August 3.61 1.81 September 3.33 1.84 October 3.46 2.09 November 3.97 2.22 December 3.74 1.74 ----- ---- Spring 10.67 4.09 Summer 9.18 6.00 Autumn 10.76 6.15 Winter 10.42 4.45 ----- ----- Year 41.03 20.69

Another very striking difference between the two countries is shown by a comparison of the quant.i.ty of water falling in single days. The following table, given in the Radcliffe Observatory Reports, Oxford, England, 15th volume, shows the proportion of very light rains there.

The observation was in the year 1854. Rain fell on 156 days:

73 days gave less than .05 inch.

30 " between that and .10 "

27 " between .10 " .20 "

9 " " .20 " .30 "

9 " " .30 " .40 "

4 " " .40 " .50 "

1 gave .60 "

2 " .80 "

1 " 1.00 "

Nearly half the number gave less fall than five-hundredths of an inch, and more than four-fifths the number gave less than one-fifth of an inch, and none gave over an inch.

There is more rain in the United States, by a large measure, than there; but the amount falls in less time, and the average of saturation is certainly much less here. From ma.n.u.script records, furnished us by Dr.

Hobbs, of Waltham, Ma.s.s., we find, that the quant.i.ty falling in the year 1854, was equal to the average quant.i.ty for thirty years, and that rain fell on fifty-four days, in the proportion as follows:

Number of rainy days, 54; total rain-fall, 41.29.

0 days gave less than .05 inch.

2 " between that and .10 "

8 " between .10 " .20 "

7 " " .20 " .30 "

5 " " .30 " .40 "

4 " " .40 " .50 "

2 " " .50 " .60 "

4 " " .60 " .70 "

4 " " .70 " .80 "

3 " " .80 " .90 "

0 " " .90 " 1.00 "

0 " " 1.00 " 1.10 "

2 " " 1.10 " 1.20 "

1 " " 1.20 " 1.30 "

1 " " 1.30 " 1.40 "

3 " " 1.40 " 1.50 "

2 " " 1.50 " 1.60 "

1 " " 1.60 " 1.70 "

2 " " 1.80 " 1.90 "

1 " " 2.30 " 2.40 "

1 " " 2.50 " 2.60 "

1 " " 3.20 " 3.30 "

No rain-fall gave less than five-hundredths of an inch; and more than one-fourth the number of days gave more than one inch. In 1850, four years earlier, the rain-fall for the year, in Waltham, was 62.13 inches, the greatest recorded by observations kept since 1824. It fell as shown in the table:

Number of rainy days, 58; total rain-fall, 62.13.

3 days gave between .05 and .10 inches.

4 " .10 " .20 "

6 " .20 " .30 "

3 " .30 " .40 "