CHAPTER XXI.
ON CLOVER SICKNESS.
In considering the important question involved in the term “Clover sickness,” we would first direct attention to the fact that crop clover is a derivative plant which has been so forced that it is many times larger and more juicy and succulent than the wild plant from which it sprung. This derived nature (the propensity, as it were, for fattening) can only be maintained by a continuance from one generation to another of those luxuries to which the cultivated family has been accustomed; hence, then, if seed be brought from a richer soil to a poorer, or from a warmer to a colder climate, we may expect that its plants grown amid barley and drawn up during the summer would have but a poor constitution to withstand the rigours of winter; but can we in such a case say that the land is clover-sick, that is, sick of growing clover?
Of course the seed here supposed will grow better in one place than in another, as, for example, we have traced some American seed of broad-leaved clover grown by itself in a deep rich soil in the Vale of Gloucester, where the climate is so much milder as to be a fortnight before the elevated land of the Cotteswold Hills and producing an abundant crop; while the same forming part of a mixture of “seeds” with rye-grass and plantain on the hills, the two latter have taken possession of the soil, and the clover made no progress at all; whilst other seed, under precisely the same circumstances, has done remarkably well.
That there is much reason for these conclusions will be found in the fact that the more seed we import from warmer climates the more difficult is it found to make the land produce a plant; still importation is rapidly on the increase, because warmer climates can produce seed more certainly and in greater quantity than we can at home.
The difficulty of growing from foreign seed increases in proportion to the thinness of the soil and the backwardness of the climate, so that the elevated districts on the stony Cotteswolds just adverted to present, perhaps, more of the so-called clover-sick land than any other of like extent.
The seed of clover, then, has become more and more pampered—more the offspring of large crops from deep alluvial soils under the tropical summer heat of the south of France and the United States, where it is grown as a self-crop and not fed merely on what the corn could not carry away; and so while this enervation, or, if preferred, this civilization, of plant has gone on, we expect its seed all at once to withstand the shock of a lower temperature with constant climatal changes and cutting winds; and if it does not succeed, we say that the land is clover-sick, when, in truth, it is the seed that sickens under these new and trying conditions. As well may we say that the Northern States sicken of the negro, because he there dies out so rapidly, or that the warm south sickens of humanity, because those who are unacclimated sicken and die there.
Another circumstance which has contributed to an increased difficulty in growing clover on thin soils will be found in the farmer discarding as antiquated the practice of paring and burning, which was formerly the usual preparation for the turnip crop. In a paper on “Paring and Burning,” in the 18th volume of the Journal of the Royal Agricultural Society, Professor Voelcker remarks:—
The ashes produced by paring and burning are especially useful to turnips, and also to other green crops, because they contain a large proportion of phosphates and potash—constituents which, it is well known, favour in a high degree the luxuriant growth of root-crops.
Further, the learned professor closes a most able paper with the following conclusions:—
Paring and burning, instead of being an antiquated operation, is a practice the advantages of which are fully confirmed and explained by modern chemical science.
Paring and burning, to judge from our own experience, had the effect of converting some of the hard limestone brash into lime, in which case it broke up by the influences of air and rain, and so restored the lime and alumina which mostly exist together in limestone, the former of which is quickly lost in thin soils,—so much so, indeed, that not unfrequently the whole depth of soil, even upon a limestone, will often be curiously devoid of lime, which is a necessary ingredient in the constitution of a clover crop.
Again, we should conclude that the operation under discussion, from its decomposing that dark vegetable matter called humus, which is always found in large quantities on some of the soils which are called “dead,” from their inability to produce crops, and which often cause astonishment that such black, nice-looking earth should be unproductive. Now this soil, though it would favour the growth of some species of peat-loving plants, as Ling, Heath, &c., is not suitable for clover, as the wild plant is curiously absent from peaty positions.
Professor Voelcker remarks that “the excess of undecomposed organic matters in soils is decidedly injurious to vegetation. Roots, stems, and other vegetable matters remain buried in the ground for years without undergoing decomposition, and if we attentively study the subjoined analysis of soil in the neighbourhood of Cirencester, well adapted for burning, we shall see how the lime, alumina, and organic matter might be beneficially affected by the process:—
| ANALYSIS OF SOIL ADAPTED FOR BURNING, BY PROFESSOR VOELCKER. | |||
| Moisture | ·93 | ||
| Organic matter | 10 | ·67 | |
| Oxides of iron and alumina | 13 | ·40 | |
| Carbonate of lime with a little sulphate of lime | 23 | ·90 | |
| Carbonate of magnesia | 1 | ·10 | |
| Phosphoric acid | trace | ||
| Potash | ·38 | ||
| Soda | ·13 | ||
| Insoluble silicious matter | 49 | ·66 | |
| 100 | ·17 | ” | |
The ashes, however, are obtained by burning a thin slice pared from the surface of the land, so that they are derived from surface-soil and vegetable matter, the latter often yielding a sufficient amount of phosphoric acid with which to procure a crop, and, what is all important for us to consider is, that this phosphorus, the alkalies, and lime, are rendered by the burning in a state just fitted for the growth of the plants that are to be grown upon them; whereas, before the process, these ingredients were in a measure locked up, so that plants could not grow for the want of sustenance; not that it was not in the soil, but that it was insoluble. If, then, clover or any other plant had not succeeded, it would have been called “clover-sick.”
The following analysis of vegetable ashes from a field in the neighbourhood of Cirencester will well repay attentive consideration, as illustrating these points:—
| ANALYSIS OF ASHES FROM PARING AND BURNING, BY PROFESSOR VOELCKER. | |||
| Moisture and organic matter | 9 | ·12 | |
| Oxides of iron and alumina | 14 | ·56 | |
| Carbonate of lime | 17 | ·17 | |
| Sulphate of lime | 1 | ·73 | |
| Magnesia | ·40 | ||
| Chloride of sodium | ·08 | ||
| Chloride of potassium | ·32 | ||
| Potash | 1 | ·44 | |
| Phosphoric acid | 1 | ·84 | |
| Equal to bone earth | (3 | ·98 | ) |
| Soluble silica (soluble in potash) | 8 | ·70 | |
| Insoluble silicious matter | 44 | ·64 | |
| 100 | ·00 | ||
Now, that land so burnt and containing such ingredients would, after the process, refuse to grow clovers we cannot at all believe; but we do know that some of the land of a like composition will not grow even a crop of turnips until prepared as described; and though the taking a subsequent barley crop off before the clover would not tend to the improvement of the latter, it will be too often because the barley has taken all the available manurial matter, so that there is little left for the clover to feed upon. In such cases we have seen the clover saved by top dressing. Paring and burning had also a salutary effect upon the clover crop in the destruction which it wrought to various insect pests, and more especially the wire-worm, which now makes such increasing inroads upon our crops of wheat and barley, and so afterwards in the clover; so that bare patches, often of great extent, will be the consequence in every crop in the rotation. Now, these bare patches in the clover crop are often appealed to as evidence of clover-sickness, whilst we do not at the same time say that land is wheat-sick or barley-sick.
Insects, indeed, are yearly becoming more destructive, not only on account of the difference in the mode of farming, but greatly from the determined destruction of birds. The food of birds is in general very mixed, but at one season of the year, when they are breeding, they are most industrious destroyers of insects; but it is just at this time that they are kept from the crops, exactly when insects are working the most mischief: hence, then, as the exigencies of a small growing family become more and more pressing, birds are driven to feed their young upon seeds, fruits, buds, and other vegetable matters, as unsuitable to build up the constitution of the young bird as bread diet for an infant.
Let, however, our grand birds of prey be encouraged, instead of being shot by the keeper as vermin, or knocked over by the prowling bird-stuffer, in order to be perched up in a box for sale to some Cockney, who would fain be considered as fond of sport because his “den,” perchance, contains a stuffed owl, hawk, magpie, or some other specimen.
On a recent visit to Dorsetshire, on our own farm, we saw a man employed to “keep the birds” from a field where several labourers were engaged barley sowing; and it is quite true that, unless he had been there, the rooks would have as industriously followed the drill as they do the plough; but, as we thought, scarcely to pick up barley in the breeding season, when there was metal more attractive in the recently-hatched Elater obscurus, parent of the wireworm, which were thicker than we ever saw them before, and, doubtless, the disturbance of the soil brought these and two or three generations of wireworms to the surface. Now, we do not hesitate to give as our opinion that this birdkeeper would have done more good to the barley and the succeeding clover crop by picking up a hundred or two of these beetles and destroying them than by blazing away at rooks for a twelvemonth, and this certainly might have been done in an hour or two.
Still, that some soils do get incapable of growing a clover crop is pretty certain; and it may, we think, be equally settled that this does not entirely depend upon their having been exhausted of the ingredients which analysis demonstrates clover to contain, for we certainly have seen clover succeed after the burning of so-called clover-sick land; and though there is reason to think that this result was partially due to the setting free of a fresh supply of manurial ingredients, we are still convinced that the burning out of humus or peaty vegetable matter and the destruction of insects had their share in the induced change.
Still, however much we may suppose that the failure of the clover crop is influenced by the alteration of its constitution as the result of cultivation, the presence of choking weeds, or by the presence of prejudicial ingredients, especially in thin soils, there can be no doubt that the principal cause of the difficulty will be found in the fact that the corn crop with which the clover is grown exhausts the soil, in the most unsparing manner, of the very chemical ingredients which the clover requires.
Thus, if sheep are folded on a crop of turnips, the whole of this crop is converted into a manure at once available for the grain crop, by which it is quickly appropriated and then taken away. Here, then, we may suppose at starting that the clover is half starved; and, with a constitution drawn up in the effort of the plants to obtain a glance of sunshine, and weakened for the want of nourishment, it is expected to bear our inclement winters.
This argument will be made all the clearer if we place side by side the result of the analyses of barley and clovers, and especially if we consider what a quantity of mineral matter is taken in a short time, and by a crop ripening its straw and seed.
Now, if we look at these figures we shall see how much of the mineral matter required for the clover has been previously abstracted by the barley, and if at the same time we reflect that this robbery may, and too often does, co-exist with the other causes which we have instanced as tending to clover-sickness, we should no more call land sick of clover because it will not bear this crop under our exhaustive system of cultivation than we should call a barren sand wheat-sick for refusing to grow corn.
| ANALYSES OF BARLEY AND CLOVER. | ||||||
| PLAYFAIR | WAY. | |||||
| Barley Grain. | Barley Straw. | Red Clover. | White Clover. | |||
| Silica | 28·97 | 46·30 | 3·34 | 3·68 | ||
| Phosphoric acid | 35·68 | 3·22 | 6·35 | 11·53 | ||
| Sulphuric acid | 1·22 | 2·61 | 4·18 | 7·21 | ||
| Carbonic acid | 16·93 | 18·03 | ||||
| Lime | 3·06 | 7·59 | 35·39 | 26·41 | ||
| Magnesia | 8·04 | 3·55 | 11·22 | 8·15 | ||
| and loss | and loss | |||||
| Peroxide of iron | 1·94 | ? | 4·35 | ? | 0·97 | 1·96 |
| Potash | 15·61 | 22·17 | 14·85 | 14·33 | ||
| Soda | 5·03 | 0·84 | 1·40 | 3·72 | ||
| Chloride of sodium | 0·45 | 9·37 | 2·36 | 4·94 | ||
| Chloride of potassium | 2·96 | |||||
| 100·00 | 100·00 | 99·95 | 99·96 | |||
We cannot better conclude this chapter than by quoting the following from Baron Liebig’s Letters on Modern Agriculture, so ably translated by Professor Blyth:—
The simplest peasant has sense enough to see, and all agriculturists agree with him, that clover, turnips, hay, &c., cannot be sold off from a farm without most materially damaging the cultivation of the corn. Every one willingly admits that the sale and exportation of clover, turnips, &c., exercise a detrimental influence on the growing of corn. “Above all, let us take care to have plenty of fodder; the corn crop[146] will then take care of itself.” But that the exportation of corn may possibly exercise an injurious influence on the cultivation of clover or turnips; that it is, above all, indispensable to restore to the soil the mineral constituents of the corn, to enable the clover or turnip crop to “take care of itself;” in other words, that in order to grow clover, turnip, &c., we must manure the land—this is a notion utterly incomprehensible, nay absolutely impossible, for most agriculturists. For, is not the clover grown for the sake of manure? What advantage, then, would there be if it were necessary to manure again to produce the clover? This clover the farmer expects to grow for nothing.
The mutual relations existing in the order of nature between the two classes of plants are, however, as clear as daylight. The mineral constituents of the clover, turnips, &c., and of the corn, form the conditions for the production of the clover, turnips, &c., and of the corn, and they are in their elements quite identical. The clovers, &c., require for their growth a certain amount of phosphoric acid, potash, lime, magnesia,—so does the corn. The mineral constituents contained in the clover are the same as those in the corn, plus a certain excess of potash, lime, and sulphuric acid. The clover draws these constituents from the soil; the cereal plant receives them,—we may so represent it from the clover. In selling his clover, therefore, the farmer removes from his land the conditions for the production of corn. If, on the other hand, he sells his corn, there will be no clover crop in the following year; for in his corn he has sold some of the most essential conditions for the production of a clover crop.—pp. 183-5.
This discussion, then, upon the so-called clover-sickness leads us to adopt the following propositions:—
First. That the larger induced plant of our cultivated clovers has not, as a rule, that perennial constitution of the smaller wild species.
Second. Even its induced habit is much deteriorated by transportation under adverse climatal circumstances.
Third. The seed itself is often full of weeds, which, by gaining the mastery, kill out the young clover plant.
Fourth. This effect is enhanced by growing clover with barley, in which, if not smothered, it must become weakened.
Fifth. We ought not to expect to grow clover where we have taken away the necessary substances for its growth in the corn crop.