country, it is generally found impregnated with carbonate of lime; and in this state it tends, in many instances, to ameliorate the soil. Common river water also generally contains a certain portion of organisable matter, which is much greater after rains than at other times; or which exists in the largest quantity when the stream rises in a cultivated country. Even in cases when the water used for flooding is pure, and free from animal or vegetable substances, it acts by causing a more equable diffusion' of nutritive matter existing in the land; and in very cold seasons it preserves the tender roots and leaves of the grass from being affected by frost. Water is of greater specific gravity at 42° Fahrenheit, than at 32°, the freezing point; and hence, in a meadow irrigated in winter, the water immediately in contact with the grass is rarely below 40°, a degree of temperature not at all prejudicial to the living organs of plants. In 1804, in the month of March, the temperature in a water meadow near Hungerford was examined by a very delicate thermometer. The temperature of the air at seven in the morning was 29°. The water was frozen above the grass. The temperature of the soil below the water in which the roots of the grass were fixed, was 43°." Water may also operate usefully in warm seasons by moderating temperature, and thus retarding the over-rapid progress of vegetation. The consequence of this retardation will be greater magnitude and improved texture of the grosser parts of plants, a more perfect and ample developement of their finer parts, and, above all, an increase in the size of their fruits and seeds. We apprehend this to be one of the principal uses of flooding ricegrounds in the East; for it is ascertained that the rice-plant will perfect its seeds in Europe, and even in this country, without any water beyond what is furnished by the weather, and the natural moisture of a well constituted soil. "In general, those waters which breed the best fish are the best fitted for watering meadows; but most of the benefits of irrigation may be derived from any kind of water. It is, however, a general principle, that waters containing ferruginous impregnation, though possessed of fertilising effects when applied to a calcareous soil, are injurious on soils that do not effervesce with acids; and that calcareous waters, which are known by the earthy deposit they afford when boiled, are of most use on siliceous soils, or other soils containing no remarkable quantity of carbonate of lime." SUBSECT. 6. Changing the Condition of Lands, in respect to Atmospherical Influence. 2150. The influence of the weather on soils may be affected by changing the position of their surface and by sheltering or shading. 2151. Changing the condition of lands, as to solar influence, is but a limited means of improvement; but is capable of being turned to some account in gardening. It is effected by altering the position of their surface, so as that surface may be more or less at right angles to the plane of the sun's rays, according as heat or cold is to be increased or diminished. The influence of the sun's rays upon any plane are demonstrated to be as their number and perpendicularity to that plane, neglecting the effects of the atmosphere. Hence one advantage of ridging lands, provided the ridges run north and south; for on such surfaces the rays of the morning sun will take effect sooner on the east side, and those of the afternoon will remain longer in operation on the west side; whilst at mid-day his elevation will compensate, in some degree, for the obliquity of his rays to both sides of the ridge. In culture, on a small scale, ridges or sloping beds for winter-crops may be made south-east and north-west, with their slope to the south, at an angle of forty degrees, and as steep on the north side as the mass can be got to stand; and on the south slope of such ridge, cæteris paribus, it is evident much earlier crops may be produced than on level ground. The north side, however, will be lost during this early cropping; but as early crops are soon gathered, the whole can be laid level in time for a main crop. Hence all the advantage of grounds sloping to the south southeast, or south-west, in point of precocity, and of those sloping to the north for lateness and diminished evaporation. Another advantage of such surfaces is, that they dry sooner after rains, whether by the operation of natural or artificial drainage; or in the case of sloping to the south, by evaporation. 2152. Shelter, whether by walls, hedges, strips of plantation, or trees scattered over the surface, may be considered generally, as increasing or preserving heat, and lessening evaporation from the soil. But if the current of air should be of a higher temperature than that of the earth, screens against wind will prevent the earth from being so soon heated; and from the increased evaporation arising from so great a multiplication of vegetable surface by the trees, more cold will be produced after rains, and the atmosphere kept in a more moist state, than in grounds perfectly naked. When the temperature of a current of air is lower than that of the earth, screens will prevent its carrying off so much heat; but more especially scattered trees, the tops of which will be chiefly cooled whilst the under surfaces of their lower branches reflect back the rays of heat as they radiate from the surface of the soil. Heat in its transmission from one body to another, follows the same laws as light; and, therefore, the temperature of the surface in a forest will, in winter, be considerably higher than that of a similarly constituted soil exposed to the full influence of the weather. The early flowering of plants, in woods and hedges, is a proof of this: but as such soils cannot be so easily heated in summer, and are cooled like others after the sinking in of rains, or the melting of snows, the effect of the reflection as to the whole year is nearly neutralised, and the average temperature of the year of such soils and situations will probably be found not greater than that of open lands. 2153. Shading the ground, whether by umbrageous trees, spreading plants, or cover. ing it with tiles, slates, moss, litter, &c. has a tendency to exclude atmospherical heat and retain moisture. Shading, dry loose soils, by covering them with litter, or slates, or tiles, laid round the roots of plants, is found very beneficial. SUBSECT. 7. Rotation of Crops. 2154. Growing different crops in succession is a practice which every cultivator knows to be highly advantageous, though its beneficial influence has not yet been fully accounted for by chemists. The most general theory is, that though all plants will live on the same food, as the chemical constituents of their roots and leaves are nearly the same, yet that many species require particular substances to bring their seeds or fruits to perfection, as the analysis of these seeds or fruits often afford substances different from those which constitute the body of the plant. A sort of rotation may be said to take place in nature, for perennial herbaceous plants have a tendency to extend their circumference, and rot and decay at their centre, where others of a different kind spring up and succeed them. This is more especially the case with travelling roots, as in mint, strawberry, creeping crowfoot, &c. 2155. The rationale of rotation, is thus given by Sir H. Davy. "It is a great advantage in the convertible system of cultivation, that the whole of the manure is employed; and that those parts of it which are not fitted for one crop, remain as nourishment for another. Thus, if the turnip is the first in the order of succession, this crop, manured with recent dung, immediately finds sufficient soluble matter for its nourishment; and the heat produced in fermentation assists the germination of the seed and the growth of the plant. If, after turnips, barley with grass-seeds is sown, then the land, having been little exhausted by the turnip crop, affords the soluble parts of the decomposing manure to the grain. The grasses, rye-grass, and clover remain, which derive a small part only of their organised matter from the soil, and probably consume the gypsum in the manure which would be useless to other crops: these plants, likewise, by their large systems of leaves, absorb a considerable quantity of nourishment from the atmosphere; and when ploughed in at the end of two years, the decay of their roots and leaves affords manure for the wheat crop; and at this period of the course, the woody fibre of the farm-yard manure, which contains the phosphate of lime and the other difficultly soluble parts, is broken down and as soon as the most exhausting crop is taken, recent manure is again applied. Peas and beans, in all instances, seem well adapted to prepare ground for wheat; and in some rich lands they are raised in alternate crops for years together. Peas and beans contain a small quantity of a matter analogous to albumen; but it seems that the azote, which forms a constituent part of this matter, is derived from the atmosphere. The dry bean-leaf, when burnt, yields a smell approaching to that of decomposing animal matter; and in its decay in the soil, may furnish principles capable of becoming a part of the gluten in wheat. Though the general composition of plants is very analogous, yet the specific difference in the products of many of them, prove that they must derive different materials from the soil; and though the vegetables having the smallest system of leaves will proportionably most exhaust the soil of common nutritive matter, yet particular vegetables, when their produce is carried off, will require peculiar principles to be supplied to the land in which they grow. Strawberries and potatoes at first produce luxuriantly in virgin mould, recently turned up from pasture; but in a few years they degenerate, and require a fresh soil. Lands, in a course of years, often cease to afford good cultivated grasses; they become (as it is popularly said) tired of them; and one of the probable reasons for this is, the exhaustion of the gypsum contained in the soil." 2156. The powers of vegetables to exhaust the soil of the principles necessary to their growth, is remarkably exemplified in certain funguses. Mushrooms are said never to rise in two successive seasons on the same spot; and the production of the phenomena called fairy rings has been ascribed by Dr. Wollaston to the power of the peculiar fungus which forms it, to exhaust the soil of the nutriment necessary for the growth of the species. The consequence is, that the ring annually extends; for no seeds will grow where their parents grew before them, and the interior part of the circle has been exhausted by preceding crops; but where the fungus has died, nourishment is supplied for grass, which usually rises within the circle, coarse, and of a dark green color. 2157. A rotation is unnecessary, according to Grisenthwaite; and, in a strict chemical sense, what he asserts cannot be denied. His theory is a refinement on the common idea of the uses of a rotation stated above; but by giving some details of the constituent parts of certain grains and certain manures, he has presented it in a more clear and striking point of view than has hitherto been done. To apply the theory in every case, the constituent parts of all manures and of all plants (1st, their roots and leaves, and 2dly, their seeds, fruits, or grains,) must be known. In respect to manures this is the case, and it may be said to be in a great degree the case as to the most useful agricultural plants; but, unfortunately for our purpose, the same cannot be said of garden productions in general, though no branch of culture can show the advantage of a rota tion of crops more than horticulture, in the practice of which it is found that grounds become tired of particular crops, notwithstanding that manures are applied at pleasure. If the precise effects of a rotation were ascertained, and the ingredients peculiarly neces sary to every species pointed out, nothing could be more interesting than the results of experimental trials; and whoever shall point out a simple and economical mode by which the potatoe may be grown successively in the same soil, and produce annually, neglecting the effects of climate, as dry and well-flavored tubers, or nearly so, as they generally produce the first and second years on a new soil, will confer a real benefit on society. That wheat may be grown many years on the same soil by the use of animal manures, or such as contain gluten, Grisenthwaite's theory would justify us in believing chemically; and it ought to be fairly tried by such cultivators as Coke and Curwen. Till this is done in the face of the whole agricultural world, and the produce of every crop, and all the particulars of its culture, accurately reported on annually, the possibility of the thing may be assented to from the premises, but will not be acted on; and, in fact, even the best agricultural chemists do not consider that we are sufficiently advanced in that branch of the science to draw any conclusion, à priori, very much at variance with general opinion and experience. It should always be kept in mind, that it is one thing to produce a crop, and a different thing to grow crops with profit. 2158. The principles of rotations of crops, are thus laid down by Yvart and Ch. Pictet (Cours complet d'Agriculture, articles Assolement, and Succession de Culture; and Traité des Assolemens. Paris, 8vo. The first principle, or fundamental point is, that every plant exhausts the soil. The second, that all plants do not exhaust the soil equally. The third, that plants of different kinds do not exhaust the soil in the same manner. The fourth, that all plants do not restore to the soil the same quantity, nor the same quality of manure. The fifth, that all plants are not equally favorable to the growth of weeds, 2159. The following consequences are drawn, from these fundamental principles : First. However well a soil may be prepared, it cannot long nourish crops of the same kind in succession, without becoming exhausted. Second. Every crop impoverishes a soil more or less, according as more or less is restored to the soil by the plant cultivated. Third. Perpendicular rooting plants, and such as root horizontally, ought to succeed each other. Fifth. Two plants favorable to the growth of weeds, ought not to succeed each other. Sirth. Such plants as eminently exhaust the soil, as the grains and oil plants, should only be sown when the land is in good heart. Seventh. In proportion as a soil is found to exhaust itself by successive crops, plants which are least exhausting ought to be cultivated. 2160. Influence of rotations in destroying insects. Olivier, member of the Institute of France, has described all the insects, chiefly tipulæ and muscæ, which live upon the collar or crown of the roots of the cereal grasses, and he has shewn that they multiply themselves without end, when the same soil presents the same crop for several years in succession, or even crops of analogous species. But when a crop intervenes on which these insects cannot live, as beans or turnips, after wheat or oats, then the whole race of these insects perish from the field, for want of proper nourishment for their larva. (Mem. de la Societé Royal et Centrale d'Agr. de Paris, vol. vii.) CHAP. II. 2161. Every species of matter capable of promoting the growth of vegetables may be considered as manure. On examining the constituents of vegetables, we shall find that they are composed of oxygen, hydrogen, carbon, and nitrogen, or azote, with a small proportion of saline bodies. It is evident, therefore, that the substances employed as manure should also be composed of these elements, for unless they are, there will be a deficiency in some of the elements in the vegetable itself; and it is probable that such deficiency may prevent the formation of those substances within it, for which its peculiar organisation is contrived, and upon which its healthy existence depends. The elementary bodies above enumerated are all contained in animal, and the three first in vegetable matters. Sometimes vegetables, though very seldom, contain a small quantity of nitrogen. As certain salts are also constantly found to be present in healthy living vegetables, manures or vegetable food may, consequently, be distinguished into animal, vegetable, and saline. The authors whom we have already mentioned (2065.) as producing the first chemical treatises on soils, were also the first to treat chemically of manures. Of these, the latest in the order of time is Sir H. Davy, from whose highly satisfactory work we shall extract the greater part of this chapter. SECT. I. Of Manures of Animal and Vegetable Origin. 2162. Decaying animal and vegetable substances constitute by far the most important class of manures, or vegetable food, and may be considered as to the theory of their operation, their specific kinds, and their preservation and application in practice. SUBSECT. 1. The Theory of the Operation of Manures of Animal and Vegetable Origin. 2163. The rationale of organic manures is very satisfactorily given by Sir H. Davy, who, after having proved that no solid substances can enter in that state into the plant, explains the manner in which nourishment is derived from vegetable and animal sub stances. 2164. Vegetable and animal substances deposited in the soil, as is shown by universal experience, are consumed during the process of vegetation; and they can only nourish the plant by affording solid matters capable of being dissolved by water, or gaseous substances capable of being absorbed by the fluids in the leaves of vegetables; but such parts of them as are rendered gaseous, and pass into the atmosphere, must produce a comparatively small effect, for gases soon become diffused through the mass of the surrounding air. The great object, therefore, in the application of manure should be to make it afford as much soluble matter as possible to the roots of the plant; and that in a slow and gradual manner, so that it may be entirely consumed in forming its sap and organised parts. 2165. Mucilaginous, gelatinous, saccharine, oily, and extractive fluids, carbonic acid, and water, are substances that in their unchanged states contain almost all the principles necessary for the life of plants; but there are few cases in which they can be applied as manures in their pure forms; and vegetable manures, in general, contain a great excess of fibrous and insoluble matter, which must undergo chemical changes before they can become the food of plants. 2166. The nature of the changes on these substances; of the causes which occasion them, and which accelerate or retard them; and of the products they afford, have been scientifically stated and explained by our great agricultural chemist. If any fresh vegetable matter which contains sugar, mucilage, starch, or other of the vegetable compounds soluble in water, be moistened, and exposed to air, at a temperature from 55° to 80°, oxygen will soon be absorbed, and carbonic acid formed; heat will be produced, and elastic fluids, principally carbonic acid, gaseous oxide of carbon, and hydro-carbonate will be evolved; a dark-colored liquid, of a slightly sour or bitter taste, will likewise be formed; and if the process be suffered to continue for a time sufficiently long, nothing solid will remain, except earthy and saline matter, colored black by charcoal. The dark-colored fluid formed in the fermentation always contains acetic acid; and when albumen or gluten exists in the vegetable substance, it likewise contains volatile alkali. In proportion as there is more gluten, albumen, or matters soluble in water, in the vegetable substances exposed to fermentation, so in proportion, all other circumstances being equal, will the process be more rapid. Pure woody fibre alone undergoes a change very slowly; but its texture is broken down, and it is easily resolved into new aliments, when mixed with substances more liable to change, containing more oxygen and hydrogen. Volatile and fixed oils, resins, and wax, are more susceptible of change than woody fibre, when exposed to air and water; but much less liable than the other vegetable compounds; and even the most inflammable substances, by the absorption of oxygen, become gradually soluble in water. Animal matters in general are more liable to decompose than vegetable substances; oxygen is absorbed and carbonic acid and ammonia formed in the process of their putrefaction. They produce fetid, compound, elastic fluids and likewise azote: they afford dark-colored acid and oily fluids, and leave a residuum of salts and earths mixed with carbonaceous matter. 2167. The principal animal substances which constitute their different parts, or which are found in their blood, their secretions, or their excrements, are gelatine, fibrine, mucus, fatty, or oily matter, albumen, urea, uric acid, and different other acid, saline, and earthy matters. 2168. General treatment of organic manures. Whenever manures consist principally of matter soluble in water, it is evident that their fermentation or putrefaction should be prevented as much as possible; and the only cases in which these processes can be useful, are when the manure consists principally of vegetable or animal fibre. The circumstances necessary for the putrefaction of animal substances are similar to those required for the fermentation of vegetable substances; a temperature above the freezing point, the presence of water, and the presence of oxygen, at least in the first stage of the process. To prevent manures from decomposing, they should be preserved dry, defended from the contact of air, and kept as cool as possible. Salt and alcohol appear to owe their powers of preserving animal and vegetable substances to their attraction for water, by which they prevent its decomposing action, and likewise to their excluding air. SUBSECT. 2. Of the different Species of Manures of Animal and Vegetable Origin. 2169. The properties and nature of the manures in common use should be known to every cultivator: for as different manures contain different proportions of the elements necessary to vegetation, so they require a different treatment to enable them to produce their full effects in culture. 2170. All green succulent plants contain saccharine or mucilaginous matter, with woody fibre, and readily ferment. They cannot, therefore, if intended for manure, be used too soon after their death. Hence the advantage of digging or ploughing in green crops, whether natural, of weeds, or sown on purpose; they must not, however, be turned in too deep, otherwise, as Mrs. Ibbetson has shown (Philos. Mag. 1816), fermentation will be prevented by compression and exclusion of air. Green crops should be ploughed in, if it be possible, when in flower, or at the time the flower is beginning to appear, for it is at this period that they contain the largest quantity of easily soluble matter, and that their leaves are most active in forming nutritive matter. Green crops, pond-weeds, the paring of hedges or ditches, or any kind of fresh vegetable matter, require no preparation to fit them for manure. The decomposition slowly proceeds beneath the soil; the soluble matters are gradually dissolved, and the slight fermentation that goes on, checked by the want of a free communication of air, tends to render the woody fibre soluble without occasioning the rapid dissipation of elastic matter. When old pastures are broken up and made arable, not only has the soil been enriched by the death and slow decay of the plants which have left soluble matters in the soil, but the leaves and roots of the grasses, living at the time, and occupying so large a part of the surface, afford saccharine, mucilaginous, and extractive matters, which become immediately the food of the crop, and the gradual decomposition affords a supply for successive years. 2171. Rape-cake, which is used with great success as manure, contains a large quantity of mucilage, some albuminous matter, and a small quantity of oil. This manure should be used recent, and kept as dry as possible before it is applied. It forms an excellent dressing for turnip crops; and is most economically applied by being thrown into the soil at the same time with the seed. Sir 2172. Malt-dust consists chiefly of the infant radicle separated from the grain. H. Davy never made any experiment upon this manure; but has great reason to suppose it must contain saccharine matter, and this will account for its powerful effects. Like rape-cake, it should be used as dry as possible, and its fermentation prevented. 2173. Linseed-cake is too valuable as a food for cattle to be much employed as a manure. The water in which flax and hemp are steeped, for the purpose of obtaining the pure vegetable fibre, has considerable fertilising powers. It appears to contain a substance analogous to albumen, and likewise much vegetable extractive matter. It putrifies very readily. By the watering process, a certain degree of fermentation is absolutely necessary to obtain the flax and hemp in a proper state; the water to which they have been exposed should therefore be used as a manure as soon as the vegetable fibre is removed from it. Washing with soap has been successfully substituted for watering by lie. 2174. Sea-weeds, consisting of different species of fuci, algæ, and confervæ, are much used as a manure on the sea-coasts of Britain and Ireland. By digesting the common fucus, which is the sea-weed usually most abundant on the coast, in boiling water, oneeighth of a gelatinous substance will be obtained, with characters similar to mucilage. A quantity distilled gave nearly four fifths of its weight of water, but no ammonia; the water had an empyreumatic and slightly sour taste; the ashes contained sea-salt, carbonate of soda, and carbonaceous matter. The gaseous matter afforded was small in quantity, principally carbonic acid, and gaseous oxide of carbon, with a little hydro-carbonate. This manure is transient in its effects, and does not last for more than a single crop; which is easily accounted for from the large quantity of water, or the elements of water, it contains. It decays without producing heat when exposed to the atmosphere, and seems, as it were, to melt down and dissolve away. A large heap has been entirely destroyed in less than two years, nothing remaining but a little black fibrous matter. Some of the firmest part of a fucus were suffered to remain in a close jar, containing atmospheric air for a fortnight: in this time it had become very much shrivelled; the sides |