Although I have considered it of great importance to fix attention on the facilities which this country presents for prosecuting the various departments of mechanical and chemical manufacture, of which the essential circumstances and materials have been described in the preceding chapters, I am far from being forgetful of the fact, that the support of the great body of the people is, and must continue to be, derived from the soil; that the manufacture most extensive and most indispensable, is the production of food, and that agriculture, in its proper sense, is the most important of the various sources of industry which the country contains, and which it is my duty to describe. There is no country in which a very large proportion of the people is not supported by, and occupied with, agricultural pursuits. In Great Britain alone they do
p.237not constitute the majority of the population, and even there it appears, from the Census returns of 1831, that of 100 families, there were
In this country a very large majority of the people depend on the produce of the land for subsistence. Thus in 1831 it was found, that of every 100 males above 20 years of age, there were supported:
By agriculture . . . 65.7
By trade or manufacture . . . 17.4
Otherwise . . . 16.9
The more accurate, as well as more recent classification of the Census of 1841, gives for the occupations of the people of Ireland:
In agriculture . . . 5,406,743 or 66.1 per cent.
In trade and manufactures . . . 1,953,688 or 24.0 per cent.
In other pursuits . . . 813,535 or 9.9 per cent.per cent.
Total population . . . 8,173,966 100.0 per cent.
From the cultivation of the soil, therefore, there are at present means of subsistence to be sought for two-thirds of the entire population, and it may well be conceived, that the inquiry as to the actual nature of the soil, its productiveness and its extent, the means of increasing its fertility, and of economizing its produce, so as to give the greatest possible amount of employment and support, presents topics for discussion, important, not merely in relation to chemical or botanical philosophy, but to the gravest problems that can occupy the minds of the philanthropist or legislator.
The point of view under which the subjects of this chapter are to be considered, is different from that in which the preceding topics have been placed. Dazzled by the wondrous facilities for industrial activity which the structure of the sister kingdom presents, we had gradually sunk under a stupifying
p.238impression, that Ireland was not suited for any manufactures; and the phrase currently ran: We are an agricultural population, the English a manufacturing people; our soil and climate fit us for producing corn and cattle, whilst her mines of coal and iron, the sources of her machine power, make her the workshop of the world. The position of the two islands is, therefore, correlative, and mutually advantageous; she sends us clothing, and we send her food; from her crowded factories we receive all the products of complex manufacture, and in return she takes our corn and cattle, the raw productions of our soil. These ideas, every way prejudicial to the true interests of the people, it was necessary to oppose. That we are not destitute of the means of considerable manufacturing industry has been, I trust, already shewn, and the propriety of availing ourselves of such resources, of passing, where it is possible, from occupations yielding little employment, to those which create most demand for labour, needs, as I believe, no argument, in a country of which the heaviest calamities arise from a population able and willing to work, for which the land does not afford employment, and to which no other industrial occupation has been as yet presented.
The distinction which is drawn between an agricultural and a manufacturing population, is, indeed, much more one of social condition and of civilization, than of geographical character. Man, in his first escape from barbarism, attaches himself to the soil, becomes a shepherd, and next a farmer: as his wants become more numerous, his agricultural operations become more complex, his ingenuity increases, and the assistance he derives from the machines for abridging labour is more important. From watching cattle he passes to manufacturing food, the earth becomes a portion of his machinery, he cleans, prepares, and sets it into action, restores the worn out portions, adds such as are deficient under the form of manures, and in all the general characters of his operations resembles a manufacturing chemist, except that his product is a palateable food instead of soap or oil of vitriol. So far from there being aught antagonistic between agriculture and manufacture, the former can only be carried on, with its best effect, where the industrial
p.239arts are in a flourishing condition. The farmer requires for his clothing the produce of various manufactures, and for his protection a house made comfortable by the labours of various artizans. His plough, his machines for winnowing and threshing, have been invented for him by ingenious mechanists. On the other hand, the manufacturer must be fed. The produce of the farm finds its quickest and readiest sale in the neighbouring manufacturing town. The risk of transport to a distance, of sales to strangers, of change of markets, are all avoided where domestic industry provides for the farmer purchasers in his own country. Moreover, besides food, the manufacturer takes from the agriculturist various materials, as flax and hemp, wool and hides, which form a large part of the value of his farm produce, and yet derive their greatest value from the subsequent processes of manufacture to which they are submitted.
The two great branches of human occupation, manufacturing and agricultural, so far from being opposed or inconsistent, are thus really bound together by the strongest ties. The same principles of science regulate the operations of both, and afford similar means of amelioration. The products of both are equally necessary for the subsistence of a civilized people, and each depends for the disposal of his stock on the capabilities of the other to purchase and to pay for it. No population that is exclusively devoted to the one or to the other mode of existence, can have a healthy organization, or be considered as in a natural state. It is, therefore, important to seek for the means of advancing both together, and as I have already described the relations of this country to manufacture, I shall now pass to the circumstances under which agriculture exists in Ireland.
It will, I trust, be understood, that I do not contemplate entering into any detailed description, either of the actual condition of agriculture in Ireland, or of the various methods and systems of cultivation and improvement which have been proposed, and are now in many cases being actively discussed. Such a task would be totally foreign to my immediate object, as well as inconsistent with the necessary limits of this work.
p.240I shall only endeavour to fix attention on the general circumstances of this department of industry, the relations which it bears to other sources of employment of the people; the great features of those applications of chemical science to agriculture, which promise to benefit so materially its condition; and finally, endeavour to direct the notice of those engaged in such pursuits, to certain branches of agricultural manufacture.
Ireland has been considered as peculiarly adapted to agriculture, from the fertility of the soil, to which all travellers or writers, who were competent to judge, have borne testimony. It may, however, be useful to adduce some such evidence, and, without referring to any of older or more dubious authority, I shall briefly notice the statements of M'Culloch, of Arthur Young, and of Wakefield. In the Statistical Account of the British Empire, Mr. M'Culloch says: A large proportion of the surface of Ireland is covered with bogs and mountains, but notwithstanding this deduction it contains a great deal of most excellent land. The luxuriance of the pastures, and the heavy crops of oats that are every where raised, even with the most wretched cultivation, attest its extraordinary fertility. This is the more singular, since, as has been already observed, the soil is generally thin. Mr. Wakefield, who was himself an agriculturist of long experience, and on a great scale in England, notices, in his elaborate account of Ireland, published in 1812, the soils of Ireland as follows: A great portion of the soil of Ireland throws out a luxuriant herbage, springing from a calcareous subsoil without any considerable depth. This is one species of the rich soil of Ireland, and is found throughout Roscommon, in some parts of Galway, Clare, and other districts. Some places exhibit the richest loam I ever saw turned up with a plough; this is the case throughout Meath in particular. Where such soil occurs, its fertility is so conspicuous, that it appears as if nature had determined to counteract the bad effects produced by the clumsy system of its cultivators. On the banks of the Fergus and Shannon, the land is of a different kind, but equally productive, though the surface presents the appearance of marsh. These districts are called caucasses: the substratum is a blue silt deposited by the sea,
p.241which seems to partake of the qualities of the upper stratum, for this land can be injured by no depth of ploughing.
In the counties of Limerick and Tipperary there is another kind of rich land, consisting of a dark, friable, dry, sandy loam, which, if preserved in a clean state, would throw out corn for several years in succession. It is equally well adapted for grazing and tillage, and I will venture to say, seldom experiences a season too wet, or a summer too dry. The richness of the land in some of the vales may be accounted for by the deposition of soil carried thither from the upper grounds by the rains. The subsoil is calcareous, so that the very richest manure is thus spread over the land below, without subjecting the farmer to any labour.
Again, he says: In the north the quantity of rich soil is not very considerable, yet valleys of extraordinary fertility are found in every county, and I was not a little astonished, amidst the rocky and dreary mountains of Donegal, where there was hardly a vestige of cultivation, to find myself drop all at once into a district where the soil was exceedingly fertile. Independently of the caucasses, the richest soil in Ireland is to be found in the counties of Tipperary, Limerick, Longford and Meath. Some parts of the county of Cork are uncommonly fertile, and upon the whole, Ireland may be considered as affording land of excellent quality, although I am by no means prepared to go the length of many writers, who assert, that it is decidedly, acre for acre, richer than England.
Arthur Young, by whose exertions as Secretary to the Board of Agriculture, and his publications, the extension of agricultural knowledge in England had been so powerfully aided, says of Limerick and Tipperary: It is the richest soil I ever saw, and such as is applicable to every wish. It will fatten the largest bullock, and at the same time do equally well for sheep, for tillage, for turnips, for wheat, for beans, and, in a word, for every crop and circumstance of profitable husbandry. You must examine into the soil before you can believe that a country, which has so beggarly an appearance, can be so rich and fertile.
Besides these general statements, we are enabled to form more definite ideas of the actual amount of produce from the soil of Ireland, by means of a very elaborate inquiry instituted by Mr. Wakefield into the usual weights of the more important crops in the various parts of Ireland. He divides the country into nine agricultural districts, but as these divisions were not founded on any geological or other natural principle, having regard only to the circumstances of his tour, they need not be specially described. The averages of the numbers of all nine, shewing the average crops of the cultivated land of Ireland generally, are given in the following table, per statute acre:
|Of Wheat||from 142½lb of seed||1300lb of corn|
|Of Bere||from 132½lb of seed||2148lb of corn|
|Of Barley||from 145lb of seed||1820 of corn|
|Of Oats||from 196lb of seed||1734 of corn|
|Potatoes||from 1404lb of seed||13669lb produce|
The largest amount of produce for each kind of crop, as given by Mr. Wakefield, and which may be taken as shewing the capability of the best land, is as follows:
|Wheat, in Waterford||4200lb|
|Bere, in Limerick||4480lb|
|Barley, in Kildare, Carlow, and Meath||4480lb|
|Oats, in the East of Derry||4032lb|
|Potatoes, at Athboy, in Meath||72100lb|
In order to render our ideas more distinct, I shall here annex the statements made by some of the most eminent authorities in British and Scotch agriculture, as to the average and maximum produce of the various crops noticed above. In his valuable Treatise on Agriculture, Professor Low estimates the weight of the various kinds of crops to be, for Great Britain generally, per statute acre:
Professor Johnstone, in his excellent Lectures on Agricultural Chemistry and Geology, estimates the average crops, and the greatest recorded crops to be:
It hence appears, that the quantities which Mr. Wakefield concluded, from very extensive inquiry, to be the usual produce of the cultivated land of Ireland, and also the quantities which were the greatest obtained in the localities where the circumstances were most favourable, are almost absolutely the same as those given by the best and most recent authorities, as the usual, and as the most abundant produce of Great Britain. Yet Mr. Wakefield's work was printed in 1812, and Messrs. Johnstone and Low's in 1843. The mode of farming was, in Ireland in 1812, such as made it a matter of wonder that any crop at all should be obtained. It must, therefore, be concluded, that the naturally higher fertility of the soil compensated for the ignorance of the farmer, and brought the final result of Ireland in 1812, and Great Britain in 1843, to the equality of production which has been just illustrated.
Further confirmation of this superior fertility of the soil of Ireland, may be derived from the results to which M. Moreau de Jonnes has arrived, after an elaborate examination of the agricultural condition of the British Islands, and has published in his Statistique de la Grande Bretagne et de l'lrlande. He considers the average crops for a Hectare (2.47 statute acres), measured in Hectolitres (2.8 bushels), to be:
I have move than once stated the area of Ireland to be 20,808,271 statute acres. The precise mode of distribution of this surface requires to be now noticed. It appears from the Census inquiries of 1841, that there are:
|Of arable land||13,464,300|
|Under water (lakes and rivers)||630,825|
The uncultivated land includes bogs and mountains. It has been already shewn, that the area of bog is 2,833,000 acres, of which almost all is capable of reclamation, and of being adapted to productive husbandry, if not required as repositories of fuel. Of the mountainy land also, comparatively little is beyond the domain of agricultural enterprize. The average elevation of Ireland above the sea is not more than 450 feet, as shewn in a former chapter; very little ground indeed lies above the elevation of 600 feet. In fact, there is no district in Ireland sufficiently elevated as to thereby present serious impediments to cultivation, and scarcely an acre to which the name of incapable of cultivation can be applied. It has been calculated that of the land at present waste, 4,600,000 acres are really available for agriculture, and from my own investigations, I am inclined to consider that estimate as certainly not exaggerated.
Such being the circumstances of the soil, it would be desirable to possess an estimate of the quantity of food which the island generally affords for the support of its inhabitants and for exportation. This, however, can scarcely be at present effected. Mr. M'Culloch states, that no documents exist from which a satisfactory estimate can be formed of the total agricultural produce of Ireland, but the eminent French statistician already quoted, M. De Jonnes, has endeavoured, by a discussion of all the available results to solve the question, and he concludes, that for each of the three kingdoms, in the years 1832 and 1834, the amount of produce was as follows. I have calculated the hectolitre, which he uses, as 2.8 bushels, in reducing his numbers to the British standard of measure.
|Country||Wheat||Rye||Barley||Oats, Potatoes, and Beans|
In the case of Ireland at least, it is probable, that M. De Jonnes includes bere and bigg under the head of rye, for otherwise it is not easy to understand how the number for rye becomes so great. It may afford some additional interest to mark the quantity of different kinds of corn exported to Great Britain. Three decennial periods are taken for comparison. The quantities expressed are quarters.
|Years||Wheat and Wheatflour||Barley and Bere||Oats and Oatmeal||Beans and Peas|
Among other interesting inquiries as to the social physics of Ireland, which are included in the census of 1841, is the estimate of the numbers and value of live stock. The numbers are given in the following table, the values are not of interest here, but the total money value may be mentioned as somewhat above twenty millions sterling.
|Horses and Mules||168,753||160,378||155,425||68,013||552,569|
The horses kept for luxury are here included amongst those employed in agricultural and other labour.
In connecting with this notice of the actual circumstances and fertility of the soil, the important question of how its powers may be augmented, or at least protected from that deterioration to which the experience of ages has proved cultivated land to be exposed, it becomes necessary to advert to the kind of action which plants exercise upon the soil, by which, in fact, their growth is sustained, and the materials of food and other crops brought into existence. I shall touch upon the subject but succinctly; considered in its proper compass, it embraces at once the principal objects of agricultural chemistry, and of vegetable physiology, departments, upon the extensive and interesting domain of which I shall not enter, but glean from them such characteristic facts and principles, as may best illustrate the immediate objects of this chapter.
The vegetable kingdom is placed in nature intermediate between the mineral kingdom, which is submitted solely to the operation of physical laws, and actuated only by means of mechanical forces, and the animal kingdom, in which vital organization is most complex and most perfect, and where physical and chemical affinities are subordinate in energy to the refined influence of nervous power. Every thing in nature is referrible to one or other of these three divisions, of which the first, the mineral, is distinguished by an absolute fixity of constitution, whilst the materials of which the animal is composed are in a constant state of change. If we consider a piece of marble, it contains carbon, oxygen, and calcium, and as long as it has been a piece of marble, the same portions of these elements have formed it: but if we consider an animal, it is composed of numerous elements which have little permanence of arrangement. By the very act of its living force, the materials of which it consists die, and are thrown off from the remainder, and other new elements of the same kind must be taken in their place, or else the whole animal dies. The living being, therefore, requires food to supply this want of new materials; for this food it must look abroad in nature; it must prey. The more highly organized animals (carnivorous) prey
p.247on those of an inferior vital power (herbivorous): these again on the vegetable kingdom. Thus, ultimately the different kinds of plants must supply the means of sustenance to all animal bodies, for in no case is an animal able to assimilate to its organism, or use as nutritious food, a mineral material.
When, however, the term of existence of the animal has expired, and that vitality ceasing, the physical and chemical forces come into play, its constituents are restored to the mineral kingdom. The various elements which had formed its bones and muscles, its nerves and viscera, pass into simpler forms of combination, diffuse themselves in the atmosphere, or are carried off, dissolved in water; or else, entombed beneath the surface, may reappear after the lapse of many ages, in rock formations, and thus become the indices of animal existence, of which all other trace might long before have vanished from the earth. From this mineral form, the elements of animal existence are rescued by the aid of plants. The vegetable, penetrating with its roots deep below the surface of the ground, stretching with its stem and branches into the atmosphere, and moistened by the showers, takes from these various sources the elements necessary for organic beings, elaborates them into the numerous products which are capable of being used as food, and on which animals are fed. The various departments of nature are thus correlative and mutually compensating. The same elements pass successively from the mineral to the vegetable, and from that to the animal existence, and by the dissolution of the latter, again back to the mineral kingdom, to be the foundation of another and similar series. When we see in Summer the country rich with luxuriant crops, gay with foliage and flowers, where in Winter all had appeared dead and desert-looking; when we find new generations of animals replacing those that die, and that the number of living beings does not diminish, it is important for us to recollect, that there is still no new elements added to those already existing on the globe, that the condition of the materials of our earth is of unceasing change: assuming many forms, they pass from mineral to plant, from plant to animal, and hence the growth and sustenance of an animal depends on the nature of the plants on which it is fed, and the growth and development of a plant upon the nature
p.248of the soil and the atmosphere, by which the mineral elements may be supplied to it.
The number of elements which are found existing in animals and plants amount to sixteen, of these the atmosphere and water may be considered as capable of supplying four, carbon, hydrogen, nitrogen, and oxygen, and these are they which constitute by far the greatest proportion of every organic substance. The remaining elements, though usually present in much smaller quantity, are not less essential to the healthy existence of the plant, and must be obtained from the soil on which the plant is cultivated. The soil must, therefore, be highly complex in constitution, in order that it may yield those elements. If it do not naturally contain them, they must be artificially supplied, in order that the plants may grow. Each crop removing from the soil quantities of those materials, diminishes its power of producing future crops, and hence to sustain the fertility of any soil, the exhausting tendency of its vegetation must be compensated for by suitable additions. In these few and simple propositions is contained the clue to the most refined and successful systems of agriculture, and the objects of the philosophical agriculturist, as well as the most effective means of practically advancing husbandry, consist in:
1st. Studying the composition of the soil.
2nd. Studying the action of plants upon it.
In neither point of view has the agriculture of this country been as yet considered, and hence I shall rather endeavour to indicate the route to be pursued in such inquiries, than be able to describe what has been accomplished.
The soil is formed by the decomposition of the minerals, of which the crust of the globe consists. The water which flows over the surface is absorbed into the pores and fissures of the rocks; and in winter, on freezing, it expands with such irresistible force, as to crumble down even the materials of the densest and hardest stone. The pulverulent or gravelly material so afforded, is carried down by rains or floods to the lower grounds, and spreading over the more level country forms the cultivatable soil. Independent of the mechanical action of water, the constitution of numerous rocks is such as to cause their
p.249gradual decomposition by its chemical action, as in the case of felspar and other minerals, and by the direct action of the atmosphere, all rocks which contain protoxide of iron very rapidly decompose and crumble down. Such being the origin of the soil, its constitution will be easily understood to depend on that of the rock from which it has been formed; and as on this constitution its fertility, or its power of supplying plants with the materials they require for their growth, mainly depends, it will be seen that the agricultural capabilities of a country are immediately connected with, and dependent on, its geological character. A district, of which the rock is simple in constitution, cannot furnish a fertile soil. A pure quartz rock, or a pure limestone, could only furnish from its soil to plants, lime or silica, and they should hence languish for want of other equally important elements. The edges of a geological district, where various rocks are in contact, will, therefore, always be more fertile as to soil than its interior, and the more numerous are the rocks in the neighbourhood, and the greater the diversity in their mineral character, the more complex will be the soil furnished by their decomposition, and by its power of furnishing the elements of growth to different kinds of plants, the greater will be its range and energy of fertility.
If these principles be applied to the actual condition of fertility of the soils of Ireland, they will be found borne out in a remarkable degree. The districts known to agriculturists, as being of the most remarkable fertility in Ireland, are in Ulster, about the valley of the Lagan, and in Munster, the Golden Vale which stretches from the end of the coal formation at Cashel to near Limerick. On looking to the geological map, these districts are found to contain a greater number of different kinds of rock, than any other locality in Ireland. The Lagan flows on a bed of new red sandstone, on one side of which rises the trap district of Antrim, with its underlying chalk and gypseous marls, whilst the clay-slate of Down bounds it on the south, until it is closed by the old red sandstone and mica-slate, the coal formation and tertiary clays, which occur all at the southern extremity of Lough Neagh. The Munster district lies between the sandstone and clay-slate mountains of the Galtees and Slieve Phelim. The principal
p.250rock of the low country is limestone, through which, however, protrude in various parts, masses of sandstone, and of volcanic trap, itself of complex constitution: the western boundary being the shales and grits of the Munster coalfield.
In the case of a river flowing through a great extent of country, and intersecting various geological formations, the earthy matter which it carries down, and deposits, when by the widening of the stream and the meeting of the tidal water, the force of its current ceases, possesses a similar complexity of composition and equal fertility. Thus the flat lands along a river are, when reclaimed, found to be highly productive, such are the caucasses of the Shannon, so have been formed the low districts of Holland and Belgium, whose agriculture is so worthy of imitation. So also by the overflowing of the Nile, and the deposition of its mud, the debris of the numerous rocks of the upper country, Egypt was rendered the garden of the ancient world.
It is necessary to remark, however, that the source of the soil may be, and perhaps more frequently is, far distant from the rock which actually underlies it; the soil being formed by the decomposition of the mountainous country, and being deposited on the plain. The constitution of the most usual soil of the central portions of Ireland is a remarkable instance of this. The great limestone plain is covered by a soil which contains scarcely a trace of lime, although it may be actually mixed with limestone gravel. I have examined soil which was not many inches deep, and had a subsoil of limestone gravel, resting on bare limestone rock, and yet the soil itself was almost barren for want of lime, which it was necessary to apply to it as a manure. This circumstance is very well illustrated in the remarks of Mr. Murphy, in an agricultural tour, published in the Irish Farmers' Journal: he says, speaking of the limestone country between Dublin and Slane: The surface soil of the extensive level, of which this rock forms the sub-stratum, does not appear to have been formed by the disintegration of the subjacent rock, as between it and the surface a layer of gravel or rounded stones intermixed with earth, occurs very generally; these round stones, being for the most part a limestone of much purer character, and suited for burning:
p.251but rather seems to have been deposited by the waters of immense lake, which probably at some distant period occupied this extensive flat. It has not, so far as we are aware, been analysed, but evidently contains a large portion of alumina (clay); is stiff, retentive of moisture, and if worked or trodden when wet, becomes as hard as a road in dry weather, so that no harrowing or rolling can reduce the clods, but which fall just like roche lime on being wetted.
It is very difficult to trace, in any case, the origin of soils which are mostly due to such complex sources, and especially in Ireland, where analyses are almost absolutely absent, and where the attention of scientific men has been as yet scarcely at all fixed on agricultural problems; yet, it may not be uninteresting to follow up what has been said, by noticing at least a possible source of the heavy clayey soil of the limestone plain. The coal districts of Ireland, as described in a former chapter, are not shut in, as in most other countries, and contained in basins between more elevated formations of older rocks, but stand out insulated, and rising several hundred feet above the general level of the limestone plain on which they rest. Were they always of their present limited dimensions? Were not, for instance, the Leinster and Tipperary coal fields once connected? Were not the places where the lower limestone is now the surface rock, originally covered by an extension of the calp and upper limestone, the tearing off of which laid bare the lower and produced a portion of the present soil?
The great heaps of limestone gravel known as Eskers, which are found over the central plain, and which afford abundant proof of there having been at one time currents of vast force in operation over the surface, render it highly probable, and that certainly in some localities such has occurred is beyond doubt. In the Railway Report, Mr. Griffith, describing the coal strata of Lough Allen, says: The millstone grit forms the surface, not only of Cuilcagh, but of many similar mountains of the neighbouring district. Had they been one hundred feet higher, they would have all contained the main coal of Brahlieve mountain, but unfortunately that valuable coal bed, which no doubt once existed there, has been washed
p.252away by the action of currents, proceeding from the north-west, and deposited in broken fragments, accompanied by sandstone and blue-clay, on the surface of the limestone valley which extends to the south-east, towards Belturbet, Killeshandra, and Mohill. In many instances large pieces of coal have been discovered by well-sinkers, in the diluvium, throughout the district above mentioned, and in some cases the quantity of coal was so considerable, as to induce the belief, that by sinking deeper, a bed of coal might be found. If we contemplate similar, only more extended actions than those just now described, we shall have easily accounted for the coating of clayey soil which covers the limestone country, and which certainly has been produced by the decomposition of slate-clay strata such as exist abundantly in the coal formations and in the calp.
I have mentioned that we are almost totally destitute of analyses of the soils of Ireland. This is a deficiency which it is most important for our scientific chemists, with the assistance of enlightened agriculturists, and of such institutions as the Royal Dublin Society, to endeavour with all energy to supply. In preparing the Geological Memoir for the Ordnance Survey of Londonderry, Captain Portlock had analyses made of several soils from that country, of which the following table presents a summary sufficient for present objects. The soils are arrranged according to the nature of the underlying rock, and the names of the townland of each are given.
|Sand and gravel||104.2||131.7||101.2||112|
|Fine insoluble matter||65.8||37.0||38.7||67.8|
|Oxide of iron||7.1||3.1||0.2||8.0|
|Carbonate of lime||0.2||0.0||0.0||0.0|
Soils on trap rocks.
|Sand and gravel||71.3||68.2||85.6||41.9|
|Fine insoluble matter||54.6||70.8||77.4||88.6|
|Oxide of iron||16.4||10.3||11.7||17.6|
|Carbonate of lime||0.0||3.6||9.3||0.7|
Soils on sandstone rocks.
|Sand and gravel||124.5||105.4||123.8||142.9|
|Fine insoluble matter||53.2||62.3||38.2||38.6|
|Oxide of iron||4.5||5.0||3.9||6.2|
|Carbonate of lime||0.2||0.2||0.2||0.0|
It can be easily understood, that if we were in possession of a series of analyses of the soils of the country, and could exhibit them in the form given above, they would furnish most valuable data and assistance in agricultural operations, but I must say, that really useful analyses should be very differently executed from those above detailed. In none of these are the alcalies, magnesia, the sulphates, nor phosphates, at all noticed as present or absent. Yet, these are highly important elements of a soil, and indispensable to most plants. Moreover, there is a large amount of sand and gravel mentioned, also fine insoluble matter, but no idea of the nature of the sand, gravel, or fine matter; yet the nature of this being unknown, what do we know of the soil? In fact, the analysis of a soil
p.254is an operation requiring the greatest precision. In order that we may be satisfied of its correctness, we must have the security of other and difficult problems in chemistry, successfully solved by the same analyst, whom, therefore, we can trust, but in the case of the Ordnance Survey analyses, the name of the operator is not even given, and hence we have no other authority to rely on for their accuracy, even as far as they go, than that of Captain Portlock, whose eminence in his own departments of science is indeed worthy of praise.
In no case do the above analyses of soils enable us to judge of the relation between the soil and subsoil or underlying rock. The composition of mica has been noticed already (p. 163), that of the trap or basaltic rocks which constitute the north-east of Ireland, and which contain a great variety of minerals in minute division throughout their mass, may be judged from the following analyses. No. 1 is by Kennedy, No. 2 by Berthier, No. 3 and 4 by myself.
|No. 1||No. 2||No. 3||No. 4|
|Oxide of iron||16||9.1||17.82||20.60|
From this complexity of constitution it might be expected, that the soil formed by the decomposition of these basaltic rocks should be well adapted for agriculture, but the manner in which it decomposes has not been properly investigated. The sides of the great trap dyke, which near Croagh in Tyrone cuts through the chalk, are decomposed and soft, disintegrating rapidly on exposure, and a clayey substance, evidently the result of its final change, rests against it in perpendicular beds,
p.255separating it from the chalk. This substance was analyzed by Dr. Apjohn and yielded:
Whether the fine insoluble matter of the soils of the trap district was similar to this decomposed trap, remains for future examination. In the decomposition of the trap rocks, it is certain that the oxide of iron is evolved in such a form, as to be soluble in weak acids. Hence the trap soils appear in the Ordnance Survey analyses to contain so much oxide of iron. This metal is even dissolved out of the disintegrating rock by the carbonic acid of the rain and spring water. Almost every spring in that district is impregnated with iron; of thirty specimens of water which I examined, twenty-three contained iron, and some of them were strongly chalybeate. It is hence probably, that the clayey substance formed by the decomposing trap, and analyzed by Dr. Apjohn as above, contained so little iron.
Before passing from the consideration of the composition of soils, it is necessary to add to this account of their constituents as derived from the rocks by which they are formed, some notice of the peculiar organic matter which all fertile soils contain, and to the functions of which I shall have to recur after some time. After the death of a plant, its elements, yielding to the force of their chemical affinities, enter into new arrangements, and by a series of progressive alterations, are finally converted into a dark brown material, termed popularly vegetable mould, and by chemists, humus or ulmine. When perfectly pure, this substance contains no nitrogen, and consists of, as prepared,
|From Wood||From Sugar|
Such a material is totally destitute of power on vegetation, and the confounding of it with the substances which are produced in the natural rotting of the remains of plants in the soil, has been very prejudicial to the progress of agricultural chemistry.
It is in fact found, that when vegetable matter commences to decompose, it evolves carbonic acid, and absorbs oxygen from the air, but not merely does it unite with that element, but also the nitrogen of the air is absorbed in considerable quantity, and enters into the constitution of the new product, which actually acquires thus, almost the composition of an animal substance. Two equivalents of wood C72 H48 O48 take from the atmosphere five equivalents of nitrogen, and ten of oxygen, and evolving sixteen equivalents of carbonic acid, C16 O32, are converted into a brown substance, which Hermann, whose results I am now quoting, terms nitrolin. The composition of this body, compared with that of animal flesh, is as follows:
If this nitrolin remain in contact with air and moisture, it falls into decomposition precisely as animal bodies do, evolves carbonic acid and ammonia, and produces different brown and black coloured substances, true humine, humic acid, &c, which are gradually less rich in nitrogen. It is by the gradual formation, and decomposition of this body, that the organic matter of the soil becomes so powerful an agent in its fertilization.
The roots and fibres of a crop, left in the soil, gradually rot, and become thereby the means of absorbing from the atmosphere a quantity of nitrogen, which is rendered available for the sustenance of the next generation of plants.
In estimating the fertility of a soil, therefore, it is most important to determine the quantity of these active organic matters, and particularly the amount of nitrogen which they contain. In the Ordnance Survey analyses, the quantity of organic matter is given, but its amount is such, often more than 20 per cent., as to show that there are included all the unaltered roots and fragments of plants, which deprive the number of all absolute value. The mere presence of organic matter indicates nothing; thus a peaty soil may be absolutely barren, if the decomposition of its organic matter has been carried on under water, where the oxygen and nitrogen of the air have not access, and consequently only inert ulmine, destitute of the power of evolving carbonic acid, and ammonia, be produced.
The office of the soil is not merely to afford such chemical elements as the constitution of the plant requires, but also, and what, in an agricultural point of view, is nearly of as great importance, to afford a mechanical support to the plant during its existence. This support must be consonant to the habits and structure of the plant, and hence the special classification of soils as adapted for the cultivation of various kinds of crops, quite independent so far of their chemical composition. Thus if we take a tenacious clay, which, when dry, becomes hard and solid, and when wet, forms an impervious paste, it is evident that plants which either required to extend delicate roots to a distance, or to generate a single root of considerable bulk, could not grow there in a healthy manner, whilst a light and very porous soil would be adapted naturally for such crops. On the other hand, a plant of which but little stretches under ground, the stem and other portions presenting a considerable mass and surface to the air, would find in a tenacious clay, a sure anchorage and support against the effects of the wind and rain. It is thus that wheat and turnip soils are almost synonymous with stiff and adhesive clays on the one
p.258hand, light and friable loams upon the other, and similar instances of the mechanical adaptation of soils to agricultural practices will have occurred in the experience of every practical farmer.
It is not merely, however, in this mechanical point of view, that the physical properties of the soil become important, but also, and indeed specially, as affecting the condition of drainage of the ground. The greater or less dryness of a soil influences powerfully the nature of the vegetation it tends to nourish. The plants of a marsh differ from those of a dry upland, not merely in greater or less abundance or luxuriance, but in nature and in organization. The plant which is naturally formed for dry ground will no more flourish in a wet situation, than an animal, inhabitant of the land or air, can seek its subsistence, and live habitually under water. It is, therefore, of vital importance to agriculture, that all superfluous water should be as rapidly as possible removed. Its presence not merely affects the character of the natural vegetation, and renders the soil unfit for the cultivation of plants which belong to a dry situation, but, what is even more practical in its consequences, it retards the progress of vegetation in a very material degree, by preventing the rays of the sun from warming the substance of the soil. A certain moderate heat is indispensable to vegetation; an increase of heat, provided it do not exceed certain bounds, augments its rapidity and force, in a remarkable degree, and the constitution of ordinary soil, by its dark colour and rugged dull aspect, is precisely such as to absorb the heat of the sun with most effect, so as to advance the vegetation on its surface; but if the soil be sensibly wet, no heating effect can take place, all the warmth will be absorbed in producing evaporation of water from the surface, and rather, as one may verify by holding a wet hand in the air, even before the sun, an impression of greater cold will be produced. Long experience as to the result has even fixed in ordinary language the word cold as expressing the imperfection of such soils. The remedying of this evil, as of the former one, consists in relieving the soil from the excess of water which lies upon it, which is to be effected by attending to the
p.259general drainage of the district, and by lessening the retentive quality of the individual soil where such is economically practicable.
The question of drainage becomes of very considerable importance in relation to the lands of the limestone plain, which, being situated at such moderate altitude, and with so gentle an inclination of surface, the rivers and lakes, on any considerable fall of rain, are apt to overflow their banks, and flooding considerable districts, destroy a serious amount of agricultural produce. Thus the Shannon, above Lough Derg, was used to flood, at ordinary rises, 32,000 acres of land along its banks, which on being relieved by the improvements in the channel of the river, from such a source of loss, will be very materially increased in value. The fall available for drainage in this district may, in a general point of view, be calculated from the fact, that the summit level of the Royal Canal is 322 feet at Mullingar, that of the Grand Canal at the summit level 279 feet above the level of the sea. The discharge of waters into the Shannon occurs where the river is 120 feet, and to the east on the edge of the limestone plain, a few miles from Dublin (about Lucan), 150 feet above that level. The fall on the plain is, therefore, but about 165 feet on each side of the summit, a distance in average of forty miles, which gives little more than four feet per mile. It is hence easily intelligible how with the obstacles of various kinds found in the course of every stream, these flat portions of the country are liable to flooding in the wet seasons. In many districts these accidents became almost truly periodical, occurring once in three or four years to such an extent as to destroy the crops; the property lost in a single year being so great, that it would, if judiciously expended, pay the entire cost of remedying the evil. A great portion of such lands is in wet seasons covered with water for three, six, or even eight months in the year, and the injury extends even to those lands, which lying higher, are not actually flooded, but the corn and other crops of which are deteriorated by the damp fogs and vapours arising from the flooded lands, and the cold and early frost thereby produced.
These evils are often augmented by the position of mills or
p.260factories which, by the injudicious construction of their clams or weirs, throw back the water on the land at one season, though they are left short of water for work at other times. In the majority of cases, the improvement of the water power of the mill and the effectual drainage of the lands are perfectly compatible. Such undertakings, however, cannot be carried out by any individual effort, except in very peculiar localities. This difficulty has, however, been recently removed, and power granted to the Board of Works to carry on drainage operations. From this the greatest benefit may be expected to result, principally to the agriculturist, but also to the manufacturer requiring water power. The land will be brought into a better state for cultivation, the supply of water to mills may be rendered steadier and even increased, as the loss by evaporation from a great flooded surface will be obviated, and by the body of water being confined more strictly to the river channels, the navigation of these will be, in many cases, materially facilitated.
That the advantages derivable from effective drainage are fully appreciated by our agricultural proprietors, is shewn by the fact, that although the powers and regulations of the Board of Works are yet but little understood by the public, there had been between August, 1842, when the Act passed, and January, 1844, applications made and surveys instituted for the drainage of 44,498 acres of land liable to flood. The estimated cost of thoroughly draining these lands amounted to £127,945, or £2 17s. 6d. per acre. The expected increase in the annual setting value of the lands amounted to £16,482 or about 13 per cent. on the capital invested, and this capital is to be derived from the parties benefited by the improvement, to whom indeed the return is rendered somewhat larger by the fact, that certain portions of the operations are carried on at the public cost. Since the commencement of the present year the applications have very much increased in number, and I am informed by Mr. Mulvany, to whom this department of the duties of the Board of Works is more specially assigned, that the total amount is not now (end of March) less than 70,000 acres.
A feature in these drainage operations which deserves notice
p.261is the amount of employment which it affords of the £127,945 estimated above as the expense of the operations, it is calculated that £96,000 would be expended in labour alone. The works are of such a simple nature, cuttings and embankments, as may be performed by the least skilled labourers and with the simplest tools. Not being necessarily limited in time, the operations of each district could be executed by the labourers of that district when agricultural occupation was most deficient, and thus at once relieve for several years the localities from the pressure of an unemployed population, ameliorate the condition of the soil, so that it may furnish additional agricultural occupation, and train the labourers to habits of steady industry.
I have thus endeavoured to trace the general conditions under which the soil of Ireland is placed, as to the circumstances of composition and of drainage, which so powerfully affect its fertile quality. It is necessary to notice also the materials which are at hand for the restoration of its powers, when, by the ordinary course of agriculture, the land becomes more or less exhausted. These materials are manures of various kinds, some mineral, some animal, or vegetable, all acting, however, in supplying to the soil the elements of which it had been originally deficient, or which had been removed from it by the crops previously grown upon the land. In order, however, that the true action of manures and the necessity of them may be understood, it will be necessary to premise some brief observations.
The great object of agriculture is to produce food for man. The agriculturist feeds various other animals, but only with the final object of rendering them also available as food. The plants must thus furnish to man the elements of which his body consists, and although there are certain exceptions arising from some kinds of food being more palatable than others, yet we may consider it as a principle, that the price of any kind of food is proportional to its nourishing quality. A stone of potatoes costs less than a stone of wheat, and this much less than fourteen pounds of beef, but to support the life of an individual it will require much more of potatoes than of wheat,
p.262much more of wheat than of beef, so that ultimately the same quantity of real nutritive material costs about the same money in all. In order that the plant may elaborate the various substances which serve the purposes of food, the plant itself must be sustained in health, and its parts properly formed, for which various substances are necessary, which are not required by the animal, and which, if the plant be eaten, are rejected. All these materials are derived from the inorganic sources described in page 246, from the air, or water, or from the soil, but it is chiefly from the latter. The atmosphere furnishes the carbon of plants, especially after they have passed the first stages of their growth, as has been shewn by Ingenhousz and many other philosophers, and so beautifully popularized by Liebig. From the atmosphere also many kinds of plants derive nitrogen, but it is from the decomposing organic matter of the soil the young plant finds a supply of carbon and of nitrogen: many of the most important plants depend on it alone for the nitrogen they contain, and in all cases the mineral elements of the vegetable are taken from the soil on which it grows. In order that the nature of these elements may be understood, I have drawn up the following tables deduced from very accurate analyses by Boussingault, in the first of which the constitution of some of the most important plants used as food is shewn, and in the last the constitution of the inorganic portion which in the first is marked as ashes.
100 parts of the following substances considered as dry, con sist of:
|Red clover hay||47.4||5.0||37.8||2.1||7.7|
100 parts of these substances in their ordinary state of moisture contain usually:
100 parts of the ashes of the substances in these tables contain:
|Moisture and loss||2.4||3.7||3.0||2.9||0.7||5.5||0.0|
The investigations of Boussingault enable us also to calculate the actual quantities of these various elements which are taken from the soil by the growing crop. Thus reducing his numbers to British standard weights and measures, he found the usual crop of wheat, from his farm in Alsace, per English acre, to weigh:
|As stored||Dried||Containing ash|
The ash consisted of, per acre:
|Grain ash||Straw ash|
|Moisture and loss||0.79||6.59|
The usual crop of oats was:
|As stored||Dried||Containing ash|
The ashes were found composed of:
|Potato ash||Turnip ash||Clover ash|
|Moisture and loss||1.20||1.27|
The other crops, of which the composition per cent. has been given above, yield usually, per statute acre, as follows:
|As stored||Dried||Containing ash|
These ashes consisted of:
|Potato ash (lb)||Turnip ash (lb)||Clover ash (lb)|
|Moisture and loss||0.99||14.02||0.00|
These analytical results show how numerous are the materials which the plants remove from the soil, and also the quantities which in each year are taken from a given area. Most of these, it will be observed, are bodies which exist in ordinary soils, but in comparatively small quantity. Thus it requires very accurate analysis to determine the presence of phosphoric acid, or of magnesia, or of potash, in a soil; and yet these bodies are found in the ashes of the growing crop in abundance. It is, therefore, easily intelligible, that plants removing thus such substances from the soil, should ultimately leave it so far destitute of them, as to be unable to afford material for the healthy growth of similar plants, the soil should become barren, and it would require long repose, indeed time sufficient for the formation of a new soil before a similar cultivation could be renewed with success. This time cannot, however, be given without such interruption of agricultural labour as should ultimately produce serious loss, and hence the necessity of pro-ducing an artificial soil, such as may supply all the materials
p.266necessary to the plants by the application of manures, and render the farmer, to a great extent, independent of the slower process by which natural soil is generated. Of these manures, it falls only within the object of this work to notice such as exist naturally in Ireland.
To the different varieties of cold clayey soils, of which so large a part of the central surface of Ireland consists, there is no manure more suitable than lime. It is also the material most easily accessible, as but one county in Ireland is destitute of it, and in the central districts it forms in general the underlying rock. It is useful first as supplying a necessary constituent of plants, next, that when applied fresh slaked and caustic, it promotes the decomposition of the vegetable remains of former crops, and thus leads to the rapid formation of those azotized organic matters which are so active in promoting the fertility of the soil, and finally by intermixture with lime, the cohesion of the clays is so materially diminished, that they become much less strongly retentive of water. Perfectly pure lime, arising from the calcination of a pure marble, would often give only such advantages to the farmer as I have just decribed, but it is to be recollected, that no limestone is absolutely pure. That class of rocks are formed of the aggregated remains of animals, more or less analogous to the crustacean and molluscous animals of the existing seas, and hence contain traces of other ingredients derived from that origin. In fact if we consider the composition of existing shells, which has been found to be
|Crab Shell||Lobster Shell||Oyster Shell|
|Carbonate of lime||62.8||49.26||98.5|
|Phosphate of lime||6.0||3.22||1.0|
|Salts of soda||1.6||1.50||0.0|
|Phosphate of Magnesia||1.0||1.26||0.0|
p.267similar materials, and such is absolutely the fact. The quantities are very minute, but become not unimportant in agricultural operations from the very large amount of materials that is acted on. The different kinds of limestone also contain frequently silica and alumina, and thereby acquire often the property of setting under water and forming hydraulic limes or cements, although inferior limes for ordinary purposes. Most of the middle limestone or calp is of this quality.
Independent of the true magnesian limestone described already page 234, the beds of ordinary limestone are in various places impregnated with magnesia in small quantities, which might make them desirable for some purposes of agriculture, but injurious in other cases. The composition of such forms of limestone is exemplified in that of the stone of Murloch Bay, and of Donegal marble, the analysis of which by Dr. Apjohn is given in the following table, along with the composition of pure limestone, of that of Brown's Hill, Carlow, which belongs to the lower series, by Mr. Griffith, and of the calp of Dublin, analysed by Knox. The phosphoric acid is not counted in these analyses, as its quantity is too minute, seldom amounting to one thousandth of the entire.
|Pure Limestone||Brown's Hill||Calp||Murloch Bay and Donegal marble|
|Oxide of iron||0.0||0.0||2.0||0.0|
Marl, which under many circumstances is a most useful manure, is found to occur abundantly in Ireland. It supplies to the soil, lime, though but in a mild form; it serves to loosen the more densely aggregated soils, as it would also serve to bind those of too loose a texture. It is, in fact, a mixture of carbonate of lime and clay, and hence participates in the different
p.268properties of each. Almost all of the bogs rest on a marly bottom, intermixed with beds of clay, or of limestone gravel, in such manner that these wastes, where they become unnecessary for fuel, contain underneath the best materials for their own reclaiming. The general constitution of these marls and marly clays, is shewn in the following analyses, given in the Bog Reports by Mr. Griffith and by Mr. Edgeworth.
Strata beneath Timahoe Bog (Griffith).
|Marl||Blue and Yellow Clay|
|Carbonate of lime||64||6|
Strata under Bogs in Westmeath (Edgeworth).
|Blue Lime-Clay||White Marl||Blue Clay|
|Carbonate of lime||44.4||87.3||53.0|
|Carbonate of magnesia||1.4||0.0||0.0|
Elsewhere I shall have occasion to notice the more direct application of these materials.
A manure, of which the practical value is undisputed, although difference of opinion exists as to the mode of its action, is gypsum or sulphate of lime. The localities in which this mineral exists in Ireland have been described. Its composition is:
Sulphuric acid . . . 46.5 per cent
Lime . . . 32.6 per cent
Water . . . 20.9 per cent
Its peculiar value consists in supplying lime for the rapid
p.269growth of clover and other papilionaceous crops, which its moderate solubility in water enables it to effect, better than any other compound of that earth.
The ashes of turf arise partly from the inorganic matter belonging to the plants of which the turf was formed, and partly from intermixture of the earthy matter of the subjacent soil. It is hence that the quantity of ashes varies so considerably, as shewn in page 33, and its composition will, of course, be different as it is affected by its origin. The ashes of pure turf may be supposed nearly similar to that of other plants, except that as the material must be considerably acted upon by water, the more soluble ingredients will be found for the most part absent; thus the quantity of potash present in most ashes of plants is not found in turf ashes. The more compact varieties of turf are frequently intermixed with iron pyrites in considerable quantity, produced by reactions, not as yet thoroughly examined, and which in burning react so upon other ingredients of the plants, as to produce sulphate of soda and sulphate of lime, leaving oxide of iron free, by which the ash becomes coloured red. Hence the general rule, founded on popular experience, that red ashes are more fertilizing than white ashes, the latter being little more than clay mixed with some lime, whilst the former contains generally sulphuric acid and soda.
In a letter to the Commissioners of Irish Bogs, Sir Humphrey Davy states, that he has found a difference between the turf ashes of England and of Ireland to consist in the presence of sulphate of lime in the former, and its absence in the latter. It may be absent in certain localities, but it certainly is present in the majority of cases, as I have satisfied myself by experiment, although hitherto my opportunities have not enabled me to institute absolute analyses of the ashes of the different varieties of Irish turf, in which indeed we are as yet absolutely deficient, for Davy, though making the above remark, did not communicate any numerical results.
The following analyses of turf from various localities, made
p.270by Continental chemists, will suffice to indicate their general composition.
|Carbonic acid, Lime||63.0||2.7, 3.7||22.5, 39.7||30.0||6.0|
|Oxide of iron||9.0||33.0||11.5||305||3.7|
|Potash and Soda||0.5||0.0||0.0||0.0||2.3|
It is hence seen that whilst certain ashes, as that of Framont, could only act as a form of calcined marl, and hence be nearly useless in promoting vegetation; others contain a great number of elements, as magnesia, potash, soda, sulphuric acid, &c, which may prove in the highest degree beneficial. Differences of this kind are probably the origin of the conflicting evidence as to the results of the application of such substances as manures, by which practical agriculturists are so much puzzled, and we thus see that before employing those materials a correct knowledge of their composition should be obtained.
In none of the ashes above analysed was there phosphoric acid found, and as its presence or absence affects very materially some of the most important actions of manure, Boussingault endeavoured to ascertain whether it was at all present. He never could detect it in turf ashes, yet Sprengel names it as a constant constituent of the turf ashes of Holland and Lüneburg, in the proportion of from one to two per cent. I consider Boussingault the higher authority in such a case, which, however, is really one of the most difficult problems of chemical analysis, and, therefore, it is very desirable that special investigations
p.271should bo directed to that point in an examination of the ashes of Irish turfs.
The phosphoric acid so abundantly deposited in those parts of plants employed as food, is destined to the formation of the osseous skeleton of the animal, and on its death returns to the soil to be again absorbed into the composition of plants, and become the material of the bones of a new race of animals. Phosphate of lime and other compounds of phosphoric acid are thus most essential elements of plants, and, under the form of bones, ground or otherwise prepared, hence become one of the most usual manures. It is to be feared that before very long considerable loss will accrue to the corn and other food crops of this country, from the deprivation of the soil of this essential ingredient. The cattle exported from Ireland carry out in their bones a vast quantity of phosphoric acid derived from the soil. Of the cattle whose flesh is eaten in the country, the bones form a considerable article of export, as the attention of our agriculturists has not yet been awakened generally to the importance of restoring them to the soil. Let it be recollected, that in 1 lb. of bone there is the phosphoric acid belonging to 28lbs. of wheat, or of 250lbs. of potatoes; that this phosphoric acid is indispensable to the healthy growth of the plants and of the animals by which they are consumed, and hence will appear the vital importance to agriculture of preserving as far as possible these valuable materials, and returning them to the soil.
The coast of Ireland furnishes vast quantities of valuable manure in the sand which is dredged from a greater or less depth in the various bays, and in the sea weed which is collected at low water. Of the sea sand there are two kinds, one containing intermixed abundance of small shells, univalve and bivalve, which in many cases contain their living tenants, so that this sand used as manure supplies a very appreciable quantity of animal matter. Its general composition may, therefore, be understood, although as the proportions of its elements continually fluctuate, a single analysis of it could have but little authority. The silicious sand usually amounts to from 30 to 60 per cent.; the shells to from 20 to 50, and, beside carbonate,
p.272yield some phosphate of lime and of magnesia; there is generally from 3 to 6 per cent. of animal matter, which yields nitrogen by its decomposition, and, finally, from 5 to 10 per cent. of water, which holds in solution common salt, and the other ingredients of sea water. This manure furnishes actually thus a great variety of substances to the soil, and although its principal action must be analogous to liming, yet the farmers are certainly right in preferring it to ordinary lime.
Another variety of sea sand used as manure is the coral sand, which is found but in certain localities, as Bantry Bay, and some of the inlets of Connemara. It consists of silicious sand, intermixed not merely with ordinary sea shells, but with fragments of a material usually termed coral, but which naturalists now consider to be of vegetable origin. This, however, does not affect its chemical composition, as the organic matter, whether animal or vegetable, is very rich in nitrogen, and exceedingly active as a manure. The usual proportions of sand and coral fragments are each about 40 per cent.; the remainder being organic matter and water. The coral contains some phosphate of lime, and this variety of sand is popularly esteemed as being much preferable to that more commonly found. Boussingault considers the quantity of animal matter in it, as dredged on the French coast, where also it is much used for manure, such as to render it equal in utility to its own weight of farm-yard manure.
That I may give an idea of the extent to which the shell banks on our coasts are available as sources of these manures, I shall extract briefly some estimates of the quantities raised at Derry, and on the southern coast of Cork. The former is taken from Captain Portlock's Report on the Survey of Derry and Tyrone, the latter from a most interesting communication by Mr. Francis Jennings.
The shell banks of Lough Foyle form, when the tide is out, extensive flats, which are firm enough to be walked on without any inconvenience, and they are resorted to by numerous boats for loads of shells, and though this system has been pursued for more than a century, they exhibit no appearance of a failure in the supply. The shells hitherto examined are all of recent
p.273species; and it becomes a question whence they came. There are engaged in raising the shells
There are annually employed about 94 boats, of tonnage from below 8 to 60 tons. The aggregate tonnage of 41 of the largest boats is 1306 tons. The total quantity of shells raised each summer is about 59,496 tons, which on the shore immediately opposite the bank sell for 1s. per ton; but at Derry and Strabane for 1s. 6d. to 2s. per ton. Altogether Captain Portlock considers the shell banks of Lough Foyle to be worth £5,000 per annum to the country. They are particularly useful in bringing bad lands into cultivation, and in ameliorating stiff wet clays, deficient in calcareous matter, being applied at the rate of from 30 to 60 barrels per acre. They are preferred to lime, as warming and brittleing the land. In this the silicious sand is probably most useful in giving porosity to the clay.
Mr. Francis Jennings, to whose union of zeal and scientific knowledge I am indebted for much information regarding the industrial condition of the south of Ireland, has kindly drawn up for me the following account of the use of sea sand as a manure, along the coast of Cork. I present it without alteration, that its value and authenticity may not be lessened.
The harbours and coasts of the south and west of Ireland abound in a calcareous sand, which is employed by the agriculturist for manure in very considerable quantities; that raised in Bantry Bay and the west, is termed coral sand, from the similarity of its appearance to portions of coral, but is in reality a semi-vegetable; that kind is, however, unknown in the harbours of Kinsale, Youghal, and the intermediate districts of the coast, which, from a microscopical examination, is composed of comminuted shells, pulverized rock, portions of the shells of the crustacea, and in many cases no inconsiderable number of minute spiral and bivalve shells, containing the fish, either dead or alive.
To the large proportion of phosphate of lime contained in the crustaceous remains, and the nitrogenized matters of the
p.274fish, much of its importance, doubtless, is due. Its colour varies from a reddish brown to a blue and brownish black, dependent not alone on the remains of the shells, but also on the prevailing rock in the vicinity. The sand raised in the harbours of Cork, Kinsale, Oyster Haven, and Ringabella, is dredged from depths varying from about 10 to 30 feet; that taken in Youghal, and the bays and strands intermediate between it and Kinsale, excepting those already mentioned, is shovelled from the strand into carts and boats, generally at low water, and then taken up the country to its various destinations.
In a few of those places already named, I have been able to ascertain, with tolerable precision, the average amount raised per annum, which from Youghal harbour and strand is about 300,000 tons, 130,000 of which are taken by boats, of various degrees of tonnage, to the different landing places on the Bride and Blackwater, as far as Cappoquin.
In Oyster Haven, an inconsiderable creek west of Cork harbour, there are 32 boats, of about 12 tons burden each, employed in dredging sand, some of which make about 150 boat-loads each, in the year. These principally belong to the farmers, and the men, when paid in money for their work, earn 1s. 4d., per man for each cargo delivered, and a boat-load or two at the end of the season, as a perquisite, there being three men employed in filling and working each boat, which takes about 20 full dredges to complete its cargo; in many cases the men are partly paid by the use of a portion of land for a sufficient length of time to raise a crop of potatoes. The sand can only be raised in calm weather, and the labour is very severe. The annual amount raised in this creek is about 57,000 tons, and a boat-load, when sold, brings, according to the weather, from 6s. 6d. to 7s. 6d. These data, in connexion with the quantity raised in Cork, Kinsale, and Ringabella, which is a very small creek off Cork harbour, are by no means accurate; the amount in those places taken together is, I am confident, considerably underrated at 1,000,000 tons. Much of that raised in Cork harbour is, after a water carriage of ten or twelve miles, taken into the country on one-horse cars by
p.275working farmers a distance often and twelve miles on hilly roads, which affords strong evidence in favour of its value as a manure; and it is placed on limestone ground as well as on the soil resulting from the decomposition of the old red sandstone and carboniferous slates. It is not, however, to be supposed that the raising of sand on the coast is confined to those places already mentioned. Every strand, nook, and bay to which access can be had, by either a horse with panniers, or a cart, is taxed to supply its quota of sand; and in many places of small extent, I have seen over fifty carts taking it at low water; that which is raised then being considered the best, and only inferior to that which is dredged. When it is, therefore, considered the number of places from which sand is raised, an approximation can only be obtained by inquiries requiring no ordinary degree of care and attention.
The amount of carbonate of lime contained in the sand varies considerably; some of a dark blue colour, from Oyster Haven, which I tried a few years ago, contained 65 per cent.
It may be inquired, is the supply inexhaustible? The answer, as far as regards the dredged sand, might probably be given in the affirmative, but in many places the strands, formerly covered to the depth of many feet, at present yield none except after heavy gales, and the inhabitants must either give up its use or resort to the dredge for a supply. The amount of sand to the acre varies according to its price. In those places where it is about 6d. per ton; 800 cwt., or 40 tons, is by no means an unusual quantity to be applied every season, for many years together.
In considering its agricultural value, the quantity of salt water it contains must not be omitted, for the calculations are made not as to the amount of dry sand, but the state it is in after some hours' draining; moist to the touch, but not wet. From its daily increasing consumption, and great value when taken far inland, I believe it would form one of the most, considerable branches of internal traffic, at least in the south of Ireland, if canals existed which would allow of its being forwarded at moderate charges.
From a note furnished by the Duke of Devonshire's agent to
p.276Mr. Jennings, it appears that there are engaged in the procuring of sand at Youghal
Along the coast, large quantities of sea weed are collected for the purpose of being applied as manure, especially for potatoes. It is found that the deeper the water where it is taken up the more powerfully it acts. This is probably owing to its greater luxuriance, and containing in its tissue a greater mass of sea water, which yields valuable saline materials to the soil. Exact analyses of the sea weeds used in Ireland have not yet been made. Boussingault found those used on the coast of France to be the fucus digitatus and the fucus saccharinus. These contain, when fresh, about 40 per cent. of water, and the dry material contained from 1.58 to 2.29 of nitrogen. He considers it when fresh equivalent to about its weight of farm-yard manure. Latterly this material has been transported to considerable distances into the interior, having been first dried by exposure to the sun. Its saline constituents are, of course, those of sea water, muriate and sulphate of soda, and of magnesia, with traces of lime and iodine.
Such are the manures which the existing physical structure of the country places at the disposal of the agriculturist. They are in origin and constitution principally mineral, and are usually poor in one important element necessary to the support of plants, nitrogen. I have already noticed that to certain plants the atmosphere is itself a source of nitrogen, but it is not so to all, not even to the most important; the giving of nitrogen to the soil is, therefore, a most essential office of manures. To effect this a variety of means have latterly been afforded to the farmer, as the nitrates of potash and of soda, the salts of ammonia, the decomposed excrements of sea birds, guano, and numerous other even more complex bodies, all of which serve the purpose,
p.277all of which promote the fertility of the soil and favour the growth of plants, when judiciously applied, but none of which possess any real utility over the manure available on the farm, suitable to every crop, and most ready in its action. To this manure it is, therefore, highly important for the economical farmer to direct attention, in order that correct ideas may be formed as to the care which it deserves, and the relation which it bears to the crops, and feeding operations of the farm.
If we consider the final application of farm produce, it will appear that comparatively little of it is absolutely removed from off the ground, and that by much the larger proportion is consumed within the limits of the farm, in the provisioning and stalling of the various animals. The corn which is sold, or the animals which are sent to market, remove from the farm certain quantities of inorganic materials and of nitrogen, which must be replaced, in order to sustain its fertility, and the cost of replacing which must be considered a necessary and fair deduction from their money price; but the straw of the corn crops, the tops of turnips and potatoes, contain a much larger quantity of those materials which need not be removed from off the farm, but, on the contrary, should be most carefully returned to the soil, to serve for the support of future crops of plants. It is similarly with the produce consumed by the animals as food. Each day's food serves but to replace in its organization the materials which are daily thrown off from its frame. The dejections and excretions of the animal must, therefore, represent the food which it consumes, and thus by returning to the soil all such materials, the sustenance of the animal is really deprived of any power of diminishing the fertility of the soil. I do not here consider the case of fattening animals, but only such as are sustained in an uniform condition and health; but the fattening does not affect the principle in any important degree.
Now these various materials, the straw of the corn crops, the tops of the potatoe and turnip crops, the excretions and dejections of the animals sustained upon the farm, all mixed and subjected to the reaction which soon sets in amongst their chemical ingredients, consitute farm-yard manure. It is made-up
p.278of the remains and products of every kind of crop; it contains, therefore, the elements of every kind of crop. Its state is continually changing, as it is more or less rotted, and hence no two specimens of it would probably agree exactly in constitution, but still as illustrating in a general point of view the nature of its elements, I shall add the results of analyses made by Boussingault of that which, in a half rotted condition, he puts out on his experimental farm.
The manure, in its usual form, contains in average 79.3 per cent. of water, and 20.7 of perfectly dry material.
The dry material contained:
|Salts and earth||25.7||36.3||32.2|
The ashes of this manure contain in 100 parts:
Carbonic acid . . . 2.0
Phosphoric acid . . . 3.0
Sulphuric acid . . . 1.9
Chlorine . . . 6
Silica, sand, and clay . . . 66.4
Lime . . . 8.6
Magnesia . . . 3.6
Oxide of iron, and alumina . . . 6.1
Potash and soda . . . 7.8
On comparing this with the analyses of the ashes of various plants, given in page 263, it will be at once evident, that every constituent which they require is present in the farm yard manure. It is, therefore, of the most vital importance to those whose livelihood depends upon the produce of their farms to economize as completely as possible this valuable material.
p.279A dung-heap formed on the ordinary ground of the farm yard, allows of the escape of the most valuable portions of the manure by drainage through the porous soil. By exposure to the weather during wet seasons the most active of its elements may be washed away. These disadvantags may be removed at very trifling cost by the adoption of such modes of collecting and preserving the manure as are employed in other countries. The dung heap should be formed upon an impervious floor of brick-clay or of cement, this to dip towards the centre, so as to form a shallow tank, towards which the floors of the various stables should have such inclination as would enable the drainings to be conveyed by suitable channels to the central tank. By such an arrangement nothing goes to waste; the liability to loss by rain is obviated, and even the smallest farmer will very soon find the cost and trouble well repaid by the improvement, as well in the quantity as in the quality, of his stock of manure.
I am not disposed to underrate the importance of the various artificial and foreign manures, the effects of which on the fertility of the soil have been in many cases wonderful, often by their activity producing results to which the farm-yard manure would be incompetent, and by their portability presenting in many localities a real advantage. Nevertheless, in the existing state of education in this country, it is, as I conceive, far more useful to point out to the struggling farmer how to take advantage of the materials which now run to waste about his stables, than to send him to lay out ready money, of which he generally has so little, for a fertilizer, of whose special properties and nature he is probably quite ignorant, and which has seldom any great advantage over well prepared farm-yard manure.