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powerful, may be the manures deposited in the soil, if chemical action is not kept up in the soil, the stomach of the plant, both by the free admission and retention of heat and air. have much greater produce from a small quantity of manure under judicious cultivation, than from a great quantity when, by improper cultivation, or by those bafting tids of weather which occur so often to paralyse the efforts of the most skilful, the soil has got out of order. It is difficult to lay down rules stating how much should be ascribed to all these causes ; the skill acquired by practice, and great observation and discrimination, with repeated trials on a large scale, will all be needed to elucidate and harmonise conflicting statements.
There are particular periods in the stages of existence of plants also, when nourishing weather is more requisite, and the reverse does more harm; as in turnips, carrots, &c., newly above ground, when, if they are stunted and set up, no after nourishing weather will altogether remove the defect; or in grain crops at the time of setting the flower, in potatoes at the time of germination, &c. The different kinds of manure, also, differ very much ; some requiring much more chemical action to render them soluble than others.
In experiments, also, conducted on a small scale, on small measured portions of ground and manure, allowance must be given for variations in the state of the soil, at very short distances, in the same field. Where immense level plains or mountainous tracts of great extent occur, the soil is more uniform; but where the land, as in many districts, is undulated through its whole extent, with hill and vale, knoll and hollow, it is found that different portions of a field, within a few yards or even feet of each other, differ much in many respects. piece, having a stratum of gravel running through it, may be parched and burned up with drought in a dry season ; while in a wet season it may retain only its proper quantity. Another piece may be stiff sodden clay, suffering much when the seasons are wet and cold at the time of working, and greatly improved by working dry, and having moist weather afterwards. Another portion may have once been wet and marshy, and accumulated a kind of peaty deposit, which, if drained afterwards, may bear fine crops in ordinary seasons, but will suffer in the extremes both of drought and wet. The field may have had an excellent soil some feet deep deposited on it, but the good soil may have been washed away from some pieces by partial floods, and a stiff obdurate clay exposed: or the reverse may have taken place; the good soil may have been washed from the hills and knolls, and deposited in the hollows. All these varieties occur in the district around this, frequently in the same field. The prevailing rocks are sandstone and greenstone, above the coal measures; and the varieties produced by the mixture of these are immense.
One end of the seedling beds, along a whole quarter of the garden, may be of a loose friable, though loamy, nature, suiting most seasons well; while the other end of the beds may be found of a stiff retentive nature, which hardly any season is found to suit, yielding scarcely any crop in comparison, though covered with double the quantity both of manure and seed; yet at times, by the agency of frost, with dry digging and pulverising, these same ends may, in some seasons, be nearly equal to the other. Many districts also, from the prevalence of moor land, and the want of plantations to shelter, are much colder than others in the neighbourhood more favourably situated. Some hills slope to the south, and others to the north; some abound in inequalities, while in others the slope is regular. Fields, and pieces of fields, and gardens will also differ much, as to the quantity of organic remains left from previous crops, or deposited from the roots, or accumulated by accident. The mechanical state will also differ much, from portions being dug for the previous crop in wet or in dry weather, from trenching, draining, &c.
When so many causes are at work, which may all at times affect the results of experiments, we must not be discouraged though we do not get exact comparative results from measured portions of soils and manures; and be content, if, from a great variety of experiments carefully observed in all their bearings, on various soils, in various pieces of the same field or garden, and in various seasons and circumstances, the truth should after all begin to emerge. If these experiments give rise to theoretical opinions for which the reasons seem well grounded, and if these theoretical opinions are confirmed by future practice, a solid basis may be built, by the united aid of science and practice, which neither the one nor the other could, of itself, have so perfectly attained. The subject must be thoroughly investigated in all its bearings; and, however many deceive themselves or succeed in deceiving others, it can only be for a time. Practice will banish false theories and establish the truth, if properly and unprejudicedly observed. We must not be hasty in our conclusions, and must take proper observation of the soils experimented on, the circumstances they are placed in, the nature of the seasons, and how all these bear on one another, and may be calculated to affect or be affected by the substances deposited as manures. When practical men, generally, get so far versed in ne elements of science as to en them to follow out all these subjects in all their bearings, an immense power of observation will be brought into action, and must ultimately be productive of vast benefit.
It has been attempted to simplify the subject, by selecting some one of the constituents of manure as the most essential. Of the four principal and most abundant elements, hydrogen and oxygen being got from the water absorbed, and carbon partly from the air and partly from the soil, and not yet properly decided how much from each, nitrogen has been selected. Being generally found in combination with carbon and other substances needed as food, being necessary in the transformations carrying on in the circulating sap, assisting greatly in all the fermentations of manures, and being always found in greatest quantity in the spongioles of the roots, and in the young shoots and leaves, wherever vitality is most active, it has, though small in amount as a constituent, been found very important. It has not been found, however, that manures always produce results in proportion to the quantity of nitrogen they contain, nor that crops exhaust the fertility of the soil in the ratio of the quantity of nitrogen they take from it. It has been found, also, that great effects have taken place from an augmentation in the usual quantity of the inorganic saline substances of manures; and hence nitrogen, though perhaps the most essential ingredient taken by itself and with regard to its combinations, yet cannot generally be taken as an exact measure of value for the whole.
Dr. Madden, in his Essay published in the Highland Society's Transactions (Quarterly Journal of Agriculture) for June last, takes a more extended view of the subject, and proposes to compare the value of manures by
1st. The quantity of soluble matter present.
2d. The facility with which those portions at first insoluble can be rendered capable of solution by the process of decay.
3d. The quantity of azote (nitrogen) they contain.
4th. The whole quantity of organic matter possessed by them.
5th. The quantity of inorganic matter which each contains, possessing the same constituents as the ashes of the crop to which it is applied.
Bone dust he finds, by analysis, to contain of
Organic matter, with
some saline materials
soluble in cold water
in hot water
in a strong ditto
11.5 407 5.5 26.0 15.5
6.0 28.0 2.8
Phosphate of lime
Farm-yard manure, the average of several analyses:
45.535 soluble in water
18565 Salts of potass of soda
7.9 of lime
of silica Earthy phosphates
the phosphates in the analysis of bones having been partly contained in the easily dissolved matter.
He next compares them as to the quantities of the respective matters found in each, showing that the total organic matter and soluble matter are nearly alike: but that, as compared with farm-yard manure, there is contained in bones, of
Easily dissolved matter 2.9 times the quantity.
Thus chemical analysis shows, he says, that 1 ton of bone dust is equal to 30 tons of farm-yard manure. The same mode of analysis is also pursued with rape dust, 1 ton of which is made equal to 181 tons of farm-yard manure; and, as this nearly agrees with what is generally considered the ratio in practice, he considers that practice thus confirms scientific results.
In the above analysis, however, the phosphates are made to perform a double part, being compared, as to their action, both as phosphates and saline matter. The soluble matter in farmyard manure, also, should have been 43.565. If these had been properly attended to, the result would have been much less; probably nearer the true amount as regards practice, which he
states himself at 15 to 20. It may also be matter of doubt, that, though a certain quantity of phosphates and other saline matters is needed, we are therefore entitled to affirm that every addition to the quantity of these will produce a corresponding result. Certain quantities are needed as constituents; and, when they are abundant, the plenty of materials may produce more action. Another portion, not so easily estimated, may be needed to act chemically in the soil, in preparing the food, and in the transformations going on in the vital juices to fit them for the assimilating organs. It may be well to provide abundance; waste in these does not take place so readily as in nitrogen and carbon, but there will be a limit. If, however, we had many careful analyses of the different species of manures, conducted in the same way, they would come ultimately to be of great benefit, in enabling practical men to know, when there was a deficiency of ordinary manure, how much of the other substances should be added to make up the deficiency. When manure is required to be carried to great distances, a considerable saving of expense might be found to result from using the more concentrated manures. Peaty soils, or those abounding in brushwood, turf, leaves, branches, &c., producing carbon, are often situated at a distance from towns; and concentrated, nitrogenous, and saline manures might be carried there at much less expense. If tables were once furnished of the quantities of all the different substances drawn off by the different crops usually cultivated, and of the capability of the different manures to supply these, such as those now publishing by Professor Johnson in his Lectures; and if such tables, carefully made out, and corrected by separate analyses of plants grown in different soils and climates and in different seasons, and of manures in different stages of decomposition and in mixtures, were compared and digested; they would furnish data to enable the practical man to know, in all circumstances, how to proceed, how to supply deficiencies in manure, how to make up for exhaustion, and keep his ground properly supplied with food, so that his crops might be duly benefited by the blessings of Providence in sending good weather. To expect exact mathematical results, where so many contingencies are at work, might be Utopian; but something sufficiently near the truth may be hoped to be arrived at, so as to save a vast deal of expense, and greatly increase the value of produce. When substances are deposited as food, without a knowledge of their contents, or the requirements of the plants they are intended to feed, it is going blindly to work, and leaving to hazard what it may be in our power to provide against.
In endeavouring to elucidate the progress made in arriving at correct theoretical views on the action of the different indi