Some limited portions of the earth, as the plains of Babylon, when under skilful cultivation, the valleys of the Indus and the Nile, and the fields of Sicily, almost since the days of the flood, have produced luxuriantly, without the aid of manure to any extent; but it must be remembered the former have their fertility annually renewed by the rich overflowings of the rivers, which are charged with all the materials necessary to restore exhausted nature; while the soil of the last, being wholly of basaltic origin, is rich in the alkalies, which a year or two of rest, is sufficient to replenish in a soluble state, to be again taken up by the luxuriant crop. Hence, we have witnessed a drainage of nearly all the products from these fertile regions, for thousands of years, with impunity. But they are exceptions which only go to prove the general rule. The farmer must look to it, that all the ingredients that enter into his crops, are supplied by the materials in his soil, or a deficiency, or entire failure, will be the inevitable result.
Although all the constituents entering into the straw and grain, are absolutely essential to their perfection, they are not all equally essential to be contained in the soil. It is indispensable, however, that the earthy or inorganic portion of them be there, for these can not be obtained elsewhere. How shall they be best supplied? Ashes, it is believed, afford the cheapest, as well as one of the most effectual applications that can be made for grain. Of the ten fixed ingredients enumerated as entering into wheat, ashes yield potash, soda, lime, magnesia, sulphuric and phosphoric acids, in large proportions, and silica and iron in smaller. The chemical operation of the potash, and carbonate and sulphate of lime, however, when added to the soil, is to supply the silica, in a soluble state, from its natural condition, (it being found in abundance for this object in every soil, except in such as are formed almost exclusively of peat,) for the demands of the crop.
An increased supply of lime and gypsum, beyond what is found in the ashes, is frequently advantageous; and when the latter is beneficial, as it generally is, it should never be withheld to an extent in the highest degree useful. Of the operation of this last material, beyond yielding a portion of its sulphur to the gluten, we have as yet no satisfactory explanation. In respect to the theory of its concentrating ammonia in the soil from the atmosphere, we have very contradictory authority. Liebig asserts it, Johnstone questions it, and Dana denies it; yet the increasing fertility its application produces, would seem to give the weight of experience in favor of Liebig's views.
The chlorine and soda, if not furnished by the ashes in proportions sufficiently large, may be procured by the application of common salt, which yields both. The phosphoric acid may be obtained in any required quantity, by the addition of bones, which, dry or calcined, yield both that acid and lime, phosphate of lime constituting 86 per cent. of bones. Most soils contain alumina in abundance to furnish the food requisite for wheat; yet as it is one of the most valuable soils for this grain, both as seizing upon and retaining ammonia, and furnishing a firm foothold for the roots of the plants, it is important that lands intended for this purpose, should be adequately supplied with alumina as a top-dressing, if naturally deficient in it.
We have, then, above, all the inorganic materials for the purpose required. But there is about 97 per cent. of the crop yet to be made up of the organic constituents, carbon, oxygen, nitrogen, and hydrogen. How shall they be provided for?
First, by the selection of a calcareous or clay soil, which will furnish a proper bed for the roots of the plant, and by their peculiar mechanical texture and chemical composition, will not only hold the manures incorporated with them, but also draw some of the requisite constituents largely from the air; the former absorbing carbonic acid, and the latter ammonia.
Second, by the liberal application of common farm-yard manure, to a crop preceding that of wheat, which will leave a rich mould highly conducive to an abundant yield of perfect grain. An instance has been recently given, of a Maryland farmer raising large successive crops of wheat, by the application of putrescent manure directly upon the grain, and all injurious effects were obviated by the use of a moderate quantity of lime. This is a practice, however, which has not been found generally to be successful, causing either blight, or such rapid and luxuriant growth, as to crinkle and lodge. This effect is also produced in peaty and rich alluvial soils, where the silicate of potash, so essential to the formation of a strong, upright stalk, is not furnished in a quantity large enough for the object.
Third, the liberal use of charcoal scattered through the soil. It is claimed from its use, that the wheat crop of France has been largely augmented within the few past years. Several instances of its greatly beneficial effects, have been noticed in this country; though its influence has not hitherto been felt on wheat, by an extensive Virginia planter, in two or three recent experiments. The great power of condensing gases peculiar to charcoal, was noticed by some of the early chemists. Murray mentions it, and Saussure gives a table of results, in which he shows that perfectly dry charcoal from boxwood, will absorb 90 volumes of ammonia; 85 of muriatic acid; 65 of sulphurous acid; 55 of sulphuretted hydrogen; 35 of carbonic acid, &c. This condensation takes place in its pores, and does not produce any alteration, or new chemical compounds of the gases thus stored up; but their use in an agricultural point of view, is invaluable; for while the coal yields no fertilizing matter from its own substance, being nearly indestructible, it takes from the atmosphere in great abundance, and hoards up for the future use of the plants, one of the most evanescent, as well as most useful materials for their perfection, viz., the nitrogen contained in the ammonia.
A fourth means for procuring a good yield of wheat, is by alternating with clover, and turning in a liberal share of it as a preparation for the wheat. This is practised extensively throughout the wheat districts of the United States, and has resulted in great benefit; for besides yielding a portion of food to the grain, it keeps the ground in the best possible mechanical condition.
A fifth means, is to return all the straw and chaff to the soil, as they contain a large quantity of the identical materials required for a succeeding crop.