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soils, the matters removed are very small; and even if the phosphoric acid of the soil does not exceed a quarter per cent., it could maintain such crops for 276 years; and the same remark applies to the other elements, so that the prospect of exhaustion is, at all events, not immediate. If, continues the Professor, we next endeavor to ascertain the quantities of the elements of plants restored to the soil by farm-yard manures, we are met by the difficulty of estimating its ordinary application, and also by our still imperfect knowledge of its average composition. The number of good analyses of farm-yard manure is still small, and owing to the great difficulty of obtaining a fair sample, considerable discrepancies are found in those which have been published. By selecting, however, those results which are most trustworthy, the following table has been calculated so as to show the quantities of mineral matters and nitrogen in different quan: tities of the manure. Twelve tons have here been selected as an average application; the others, 16 and 20 tons, as quantities not unfrequently applied. The following results are expressed in pounds avoirdupois :
It thus appears that an application of 20 tons per acre is able to supply the elements of an ordinary rotation, some of them in just sufficient quantity, others in considerable excess. Such are the demands made upon the soil by the crops we cultivate; such are the supplies offered in return by our farm-yards. But after all these valuable organic matters are returned to the soil, another great supply of the elements of vegetable substances are of necessity derived from the air we breathe, and it was to render these gases available to the farmer to the greater extent that the Norfolk, or four-course husbandry was introduced.
DEEP STIRRING OF THE SOIL. Deep stirring proves beneficial to certain soils, but not to all. Indeed, it is questionable if uniform deep stirring can be profitably practiced on the greater portion of the cultivated soils in the United Kingdom. To a clearer understanding of the term "stirring," it may be necessary to state that it is used for the inversion or turning over of the soil by the plow, and is not intended to include the stirring of the soil or subsoil by any form of subsoil plow. It has been frequenlty asserted of late that all soils may be stirred to a greater depth than formerly, with an increase of their productive capabilities. Such statements should, however, be received with considerable distrust. Doubtless there are conditions which, if present, are favorable to deep stirring, but these conditions are rather exceptional than general. For instance, soils resting upon subsoils containing the constituents of plant life in higher proportions than they are present in the cultivated soil, can be profitably stirred to a greater depth, bringing a portion of the subsoil to the surface, to be incorporated with the soil. Also, where certain conditions are to be secured, deeper stirring may be advantageously followed out. For example, by increasing the amount of manurial applications, conjoined with the deeper stirring, heavier crops can be grown; the increased outlay being met by the increased produce. As a rule, it is by securing both conditions-deep stirring with frequent and liberal manuring—that the greater portions of the soils can with advantage be stirred to a greater depth than has hitherto been practiced. Whatever is the depth of soil stirred, that soil should be rendered highly fertile, and maintained in that condition by the application of manures.
Continued cropping, with the removal of a portion of the crops, will in time render most soils comparatively unproductive, however deep they are stirred. There are soils which cannot be stirred to a greater depth than formerly, without impairing their productiveness, even with an increase of manurial application. Soils of a friable, or of a retentive texture, resting upon open, porous subsoils, such as chalk, gravel, sand, &c., and soils, the texture of which has been improved by the application of clay, marl, shell-sand, &c., cannot be stirred to a greater depth without interfering in part with the improvement effected. Deeper stirring necessarily de"creases the percentage in the soil of the material which had been applied to alter its texture. An additional application of the material will doubtless correct this, but the increased outlay may not always be covered by the increased produce. There are other descriptions of soils which it is not advisable to stir to a greater depth than formerly-light, sandy, and peaty soils, resting upon subsoils of the same character as the surface soil. Compression rather than deep stirring is the best method to follow in cultivating these soils. We include in this category not only those sands or vegetable soils which drift during gales, but soils of a texture which do not move with winds. It is generally maintained that by deep stirring a greater surface is exposed to the action of the atmosphere, and consequently that the constituents of plants are present in the soil, in a state
available for plants, in an increased proportion. The removal of the crops carries away part of the organic and inorganic constituents of plants, which are not returned in the farm-yard manure. If the cultivated plants confined their rootlets to the soil which has been stirred, this argument would have some weight, but when it is considered that nearly all of the cultivated plants send rootlets into the subsoil, the necessity for deep stirring is less apparent. If it is considered that the action of the carbonie acid conveyed to the soil is to decompose the mineral constituents of the soil, and that these, when rendered soluble, are liable to be washed out of the soil by rain-water, the question of deep stirring assumes a new phase. It is quite possible that certain soils, particularly in wet localities, are deprived of the constituents of plant life in a greater degree by the annual rain-fall, than by the annual cropping. Any one studying the actions of arterial, surface, and underground drainage, particularly during a continued rain. fall, will better understand what an amount of fertilizing matter is removed by the rain-water. Rapid running streams and drains remove soluble and insoluble constituents, besides the debris of the soil in a state of suspension. Also, slow-running rivers and estuaries in many parts of the United Kingdon, contain in a state of solution and suspension, the elements of plant life apart from finely comminuted portions of the soil, to an extent which few who have not considered the question, would imagine. In some cases they have been advantageously used to increase the fertility of the soil, by warping and irrigation. Egyp: is the most notable example of fertility being maintained by the elements of plants and soils conveyed in the water. The soil of the cultivated portions of Egypt, to which irrigation is applied, has been gradually raised by the somewhat slow process of the Nile. The alluvial deposits on the banks of such outlets of rain-falls, as the Forth and Tay, show what steady causes are in operation, removing from the soil the elements of fertility. Liebig appears not to take this cause into account in his recent work on Modern Agriculture. It is a question which is open to discussion, whether or not the rain-fall conveys soluble and floating elements of vegetable life from the land to the sea in a greater extent than the whole sewerage of towns. Of course, the amount conveyed by the rain-fall depends, not alone on the quantity of rain, nor upon the depth to which the soil is stirred, but mainly on the texture of the soil, and the elevation and incline of the lands. We have little doubt that on the great proportion of the cultivated soils in wet districts in Scotland, the amount of fertilizing elements removed by the rain-water is much greater than that removed by the system of cropping pursued—that is, by a portion of the crop being sold off the farm, and the straw and turnip converted into manure and returned to the soil. It may therefore be held
that the deeper the land is stirred, the application of the elenfents of fer tility must be increased. There is no doubt that the principle of garden culture applied to the great portion of the cultivated fields, must rest on this basis. There are soils so rich in the elements of fertility, that the comparatively exhausted surface soil can be advantageously replaced by the subsoil; but such soils are very exceptional, and may be safely dismissed as not interfering with the principle we have indicted. The farmer will be most successful who expends capital in improving the manurial condition, rather than by increasing the depth of the soil stirred. With both conditions secured, heavier crops, and of a more uniform character, will be raised; but as his object is mainly profit, it is by obtaining the largest return for his capital employed, and not by raising the heaviest crops, that his object is secured.
In carrying out all operations connected with the cultivation of the soil, the question of profit and loss is the proper standard by which to test every suggestion. At present there is almost a passion in favor of deeper cultivation of the soil. It is therefore wise for farmers to weigh deliberately the pros and cons of the question.
The following enumeration may include a division of soils which, with certain directions observed, it may be found profitable to stir to a greater depth than previously:-Soils naturally deep, whether friable or retentive, which rest on a comparatively retentive subsoil. Perfect drainage is, however, one of the conditions which must be first secured. When deeper stirring is carried out, the amount of manure applied requires to be increased; the increase depending upon the natural fertility of the soil, and the mode of cropping followed. Soils which should not be deeply stirred :-light sandy, gravelly, calcareous, peaty, and vegetable soils generally, resting on subsoils of a character similar to the soil. Such soils should only be stirred deeper when substances are applied to improve their texture, such as clay, marl, lime, &c., but the depth to be stirred of the previously undisturbed soil should be inconsiderable at first, and, if deemed necessary, gradually increased. Where the subsoil is very porous, great caution should be used.
Increased manurial application is even more necessary for the profitable cultivation of such soils than those of an argillaceous nature. We may afterwards consider the question of stirring the subsoil, with the view of rendering the cultivation of certain soils more profitable.
EXHAUSTION OF THE SOIL. I wish to bring before this meeting a few facts which have come under my own observation, which tend to show the necessity of bringing the
light of science to bear upon agriculture, and prove the correctness of the theory, which Dr. Hodges has' long sought to impress upon this society, namely, that the soil cannot produce, or build up plants, unless it contains the ingredients of which such plants are composed. The soundness of this opinion is strikingly exemplified in the neighborhood of Loughgall, county Armagh, where the soil belongs to the class of sandy loams, and rests upon a limestone formation. This land was formerly considered by many to be the best in Ireland; indeed, so celebrated was it for fertility, that it was denominated “The Garden of Ireland," and a portion of the district towards Kilmore is still called "The Honey Pot,” to indicate its extreme richness. Latterly, however, this once fertile soil has been becoming less productive, and the year 1859, the wheat, in many instances, was comparatively worthless. In 1860 it was a little better, but still info rior to that in the surrounding districts, which were formerly considered unfit for the production of that valuable cereal.
Having been engaged in the wheat trade myself for more than twenty years, I observed this gradual deterioration in the quality of the grain sent to market from the district in question, and latterly tried to avoid buying any from the neighborhood, believing that the quality could not be good. Observing these things, I became convinced that the soil was being exhausted of some elements necessary for the proper development of plants, and to test the correctness of this conclusion, I procured a sample of the soil upon which inferior wheat had grown, and had it analyzed by Professor Hollges, and the result will show that this once fertile soil—this garden of Ireland—is fast approaching to barrenness, and unless a more skillful mode of husbandry be adopted, it will soon be unfit for profitable cultivation.