The Working Farmer 2(7): 158-159 (September 1, 1850)

The Composition of Land Drainage Water.
BY CUTHBERT W. JOHNSON, ESQ., F.R.S.

The following article will clearly show what matters pass through the upper soil into the under-drains, by solution from excess of rains, and the very small quantities of organic substances, even in highly manured lands, which are found in the drainage, clearly proves the power of the sub-soil to retain such matters. We could wish that the writer had experimented with soils fairly charged with carbonaceous matters, such as charcoal dust, or decomposed swamp or river muck, for he would have then found the entire organic matter to have been retained, and the inorganic alone and in smaller quantities, to pass off with the drainage. It will be observed, that in these experiments no part of the ammonia of the rain-water found its way to the drains.—[Prof. James J. Mapes, Editor]

The composition of the surplus water which in various proportions drains away from all soils, is a question of very considerable interest to the landholder. It. involves not only several great collateral objects of examination, but the result of an analysis of such water points out in many instances courses of practical inquiry as to the plants best adapted to the soil, and the elevation of the land most conducive to their prosperity, as well as the mineral or more permanent fertilisers which it will be found advantageous or useless to apply to the soil. In the course of such an inquiry it will almost invariably be found that the water which filters from a calcareous soil abounds with the carbonate of lime, with a portion of sulphate of lime; and that such waters are known to the housekeeper as the hard waters for domestic purposes. On the soils from which these waters drain, or which they are wont to cover during floods, the farmer notices the superior growth of sainfoin or lucerne, and one or two other grasses whose ashes abound with the carbonate or sulphate of lime. Such soils he finds little benefited by marling or chalking, and only to a limited extent by topdressings with gypsum (sulphate of lime.) In examining the water flowing from siliceous sand, however, or gravels, a different series of phenomena commonly present themselves. The water in such places generally contains but a small portion of carbonate of lime; they do not present the bright sparkling appearance of the waters of the chalk or other calcareous districts; they are the soft waters of every-day life. The lands from which those waters flow do not commonly produce good crops of sainfoin or the other grasses to which I have alluded; the red clover plant, too, languishes there; the ryegrass, abounding as it does in siliceous matters is unwillingly preferred by the farmers of these lands as an artificial grass. The use of calcareous fertilizers on such soils is found very beneficial: they supply a deficiency which the cultivator feels the effects of, without always being aware of the cause. The effect of such additions to the soil naturally alters the composition of the land or drainage-water (since all such waters are merely rain-water filtered through the soil) which is pretty certain to dissolve the soluble substances which it meets with in the earth. We should not, perhaps, be prepared to expect that the change in the composition of such waters was so rapid, and so considerable as it is even by the application of two or three hundred weights of guano or gypsum per acre. I have on one or two occasions in Essex had an opportunity of noticing the effect produced upon the water of a well, by a small dressing of gypsum applied to the adjoining pasture, its softness being very materially diminished, an effect, too, which continued for several months afterwards. In some experiments of Mr. J. Wilson, the present excellent Principal of the college of Cirencester, the drainage-water of a field was examined both before and after the application of a top-dressing of the soil with guano (Farmer's Almanac vol. iii., p. 247.) These trials were made in East Lothian in 1845, the water draining from the soil of a winter fallow was found by him to contain, when examined firstly on the 29th of April, (18 gallons held then 15.2 grains of solid matter,) just before being dressed with guano and sown with barley, and secondly on the 16th of May, (when 18 gallons held 27.5 grains,) the water in both cases being obtained from the same drains, the result of the comparative analysis was as follows:—

  April 29. May 16.
Organic matter and water 8.4 7.8
Silica 0.9 0.7
Silicate of alumina 0.4 0.2
Chloride of magnesium 1.12
Common salt 1.8 2.61
Carbonate of lime 2.7
Chloride of calcium 3.0 2.1
Sulphate of alumina 0.86
Peroxide of iron 2.1 2.25
Magnesia 1.69
Phosphate of lime 0.3 3.1
Phosphate of magnesia 1.8
Phosphate of alumina 0.45
 
  13.87 25.41

The turbid portion of the drainage-water first discharged first on the soil, after heavy rains, being examined by Mr. Wilson, was not found to differ materially from the drained soil: it held, however, less silica and more lime, the matter deposited by the turbid water containing per cent.

Silica 60.0
Silicate of alumina 17.5
Protoxide of iron 6.6
Sulphate of lime 8.4
Sulphate of magnesia 0.76
Phosphate of lime 0.6
Alumina 4.0
Water, &c. 1.25

These waters wore both what would be called very soft water by the housekeeper, the amount of the carbonate of lime being in one case very small, (only 2.7 grains in 18 gallons) and in the other its amount was not definable. The difference in this respect of waters from even adjacent sources of supply is very noticeable: it is a fact in every respect worthy of the serious consideration of the owners of lands which it is intended to convert into water meads. To give an instance: There is a reservoir on the common at Southampton, into which is gathered the drainage-waters of the surrounding land. This surface-water contains only about 3.2 grains of chalk per imperial gallon. Close by the reservoir a shaft has been sunk to a considerable depth down to the chalk. The water obtained from this contains 18.4 grains per imperial gallon. (Ranger's Report on the Sanitary state of Southampton, p. 98) In my own neighborhood in Surrey, the difference between the water from different sources is equally remarkable: that which flows from a spring at nearly the highest portion of the parish of Sydenham, contains only about two grains of the salts of lime; that of the Thames, furnished to the parish by the Lambeth Water Works Company, holds more than ten grains, and that of some of the water draining from the London Basin clay nearly three times this amount. At Croydon the same dissimilarity in the composition of the waters exist. That of the River Wandle containing about 16 grains of calcareous salts per gallon, that of some of the adjacent land springs varying from 17 1/2 to 48 grains per gallon.

The composition of surface-drainage water is naturally affected by the amount of the rain which falls on the land. Now this amount is not only affected very considerably by the latitude of the place, but by its elevation above the level of the sea; truths which, however applicable by the farmer, as aiding him in the choice of his rotations, are but seldom sufficiently regarded. This difference has not, in the south of England, been accurately determined by careful observations. In the north the rain-registers kept by Mr. J. F. Miller, in the lake district of Cumberland and Westmoreland, have shown some remarkable and little anticipated results. He observes, in his valuable yet cautiously drawn report, (Trans. Roy. Soc, 1849, p. 85,) that it would be premature, from the limited data already obtained, to draw any decided inference as to the gradation in the quantity of rain, at these great elevation above the sea. But it seems probable, that, in mountainous districts, the amount of rain increases from the valley upwards, to an altitude of about 2,000 feet, where it reaches a maximum, and that above this elevation it rapidly decreases. The observations made during the summer of 1846, and the year 1847, during every variety of season, confirm the above deductions in every essential particular: so that we may fairly assume he combined results to be indicative of a physical law, so far, at least, as relates to the particular locality in question, which it is observable is a most remarkably wet district.

In twenty-one months the valley, 160 feet above the
sea, received of rain a depth, in inches, equal to
170.35
Stye Head 1200 feet, 185.74
Sea-tollar common 1334 180.23
Sparkling Tarn 1900 207.91
Great Gable 2925 136.98
Sea Fell 3166 128.15

Mr. Miller notices an apparent exception to this law, in the case of the rain-guage stationed at Brant Rigg, about midway between the top of Stye Head and the Vale of Westdale, at an estimated height of 500 feet above the sea, and which, in 1847, received about one-eighth less rain than the valley. This is the only one of the guages situated on the slope of a mountain; it is on the windward side, and I imagine that, in such a position, eddies or counter-currents are produced in windy weather, which cause a less quantity of water to be deposited in the instrument than is due to the elevation. We know, indeed, that all sloping roofs, from the same cause, materially diminish the receipts of rain-guages. These observations may tempt some of my numerous country readers to examine, with easily constructed rain-guages, some of the meteorological questions, to which I have been alluding in this paper; and if they are thus led to examine into a few of the phenomena of nature, which are exhibited around them, it is almost certain that they will be rewarded by solid replies to the questions which they thus ask—answers on which they may safely rely, on many important and practical occasions.