once its habitation and its food; therefore the less a soil has to give, the more must the farmer supply, to prevent the plants starving. In very high cultivation, in which of course much is expected from the soil, it may occur in time, indeed must occur at last, that a cart-load of manure or a hundredweight of guano will not give so great an effect as at first; the cause of this however lies, not in the manure but in soil, which can no longer add so much food as before, because its store of soluble mineral substances is consumed, and the annual product of weathering is smaller than what the abundant crop requires. But this phænomenon is not at all alarming; the farmer will obtain rich crops continually from this soil, if he only-manures more richly.

XIX. ENRICHMENT AND AMELIORATION OF THE SOIL.

THE receipt to make and keep a soil continually more fertile and certain, is very simple and short; it runs, in agricultural statics: "make the soil rich and active when it is not so, and keep up this constitution when it already exists." By rich," it means (agricultural statics) the totality of the food for plants contained in a soil; by "active," the totality of powers and circumstances adapting the soil for the growth of plants, and rendering the food applicable to this; and by "yield," the product of these two factors of the produc tiveness. Attributing a determinate value to these two factors, a theory of proportions is set up, which gives in figures, the exhaustion of the soil, the return which must be given to it, the relative valuation of manures in different soils and with different crops, &c.; a balance is struck between "have" and " do," on the whole and in general, without taking note of the separate accounts of payment and receipt.

Agricultural chemistry, on the contrary, has to take into

consideration each separate account, and to trace it in detail. The richness of a soil depends upon material substances; what are these? How much of them does the soil possess? What addition can the atmosphere supply? What kind of manure promises the most perfect replacement? &c. The activity of a soil depends upon determinate chemical and physical changes, which take place in it in various ways; What is the nature of these changes? How will they be modified by composition of the soil, the tillage, the manuring, in relation to the climate of a district, the kind of crop, &c.? These and countless similar questions-work for centuries have to be discussed and answered by chemistry. When answered, the statics of agriculture will spontaneously leave the general ground which they must at present occupy, from the want of certain, special chemical facts, and assume the character of chemical statics.

In this state of the question, the rekindling of the extinguished strife, as the greater or less importance of statics or chemistry to the practical farmer, appears to me vain and unprofitable. Both have the same aim, to be of service to practice, and both have space enough to expand without restraint. If both avoid the region of arbitrary and one-sided speculation, there will be no want of opportunity of mutual support and cooperation. Chemistry furnishes new special material, statics formulate and generalize it, and practice stands in the middle as umpire, to control and to justify the statements and views of both.

The above two requirements or conditions for the increase of the productiveness of a soil, may be translated chemically about as follows. The soil must become richer: means, it must be so treated that it shall contain a good store of all the different chemical substances which plants consume in the development of their roots, stems, leaves, flowers and seeds, and this store in uniform diffusion, so that the plants may meet with plenty of them and in every part of the field. These substances are,-nitrogen, carbon, phosphoric acid, potash, lime, &c. The soil must become more active: means,it must be brought continually more into such a crumbling and soft state, that it may be accessible in the desired way to air, water and heat; that the two processes forming as it were the inner life of the soil, decomposition and

weathering, which alone render the above-mentioned richness available and enjoyable, may go on actively and uninterruptedly in it; that the atmospheric food may be ab sorbed most abundantly; that the roots of the plants may be able to spread freely both downwards and laterally, &c. The great exaltation of productiveness to be attained by the fulfilment of these conditions, is shown most distinctly in every good market-garden. If a farmer closely examines this, and the means by which it has become so rich, he will find that it can give the most eloquent and convincing lectures both in agricultural chemistry and practice. In fact, in proportion as agriculture becomes more perfect and 'higher,' it must certainly approach nearer to horticulture.

I shall try to arrange the details regarding enrichment and amelioration of the soil, according to the three principal kinds of soil; that of forests, of meadows, and arable soil.

Enrichment of the soil of Fruits and Meadows.

We meet with the simplest case of enrichment of the soil in woods and meadows which are left to themselves. H. Cotta commences his excellent 'Introduction to Forestry,' with the words," If Germany were deserted by man for 100 years it would become entirely covered with forests; as no one would make use of the litter, it would manure the earth, and not only would the forests become larger, but the soil would also become more fertile. Then if man returned and made the same demands for wood, forest-litter and cattle-pasture as at present, not only would the forests become smaller, even under the best system of arboriculture, but the soil would become less fertile." The bed of most fertile humous soil, often many feet thick, which has been produced in the course of time in the shades of the primeval forests, shows clearly enough that a dense forest, in which the fallen leaves and branches are left, becomes progressively richer.

A progressive enrichment of soil is only imaginable when it receives more than it gives out.

The case occurs most distinctly in forests and meadows when nothing is abstracted from them. But it also decidedly happens in forests even when the wood alone is removed from time to time, but the fallen litter and overgrowth of the soil left behind. The first conclusion from this is, that the soil necessarily requires

quiet companions to furnish it with the material requisite for the formation of humus, for otherwise the increase of organic substances in the soil would be altogether inexplicable. And it is so. These companions are air and water, as the soil received these in the form of rain, snow and dew. Through the respiration of man and animals, through putrefaction and decomposition and other processes, carbonic acid and ammonia are poured unceasingly into the atmosphere; both are either absorbed by the leaves of plants, or again arrive, through the medium of rain, dew, &c. in the earth, and may be then absorbed by the roots of plants. In either case they serve toward the increase of vegetable growth, as can no longer be doubted.

Recent researches have demonstrated most clearly, that not only the ammonia conveyed into the earth, but that added to the atmosphere in the gaseous form, acts most powerfully as a stimulant and a manure. In an experiment of this kind, with wheat, for example, the growth was so increased by air containing ammonia, that 19 oz. of grain and 22 oz. of straw were gathered; while only 11 oz. of grain and 12 oz. of straw were obtained from an equal quantity of wheatplants grown in ordinary air. Similar differences were met with also in the cultivation of other kinds of plants. Indeed these experiments go to prove that plants possess the power to employ in some degree for their nutrition, even the nitrogen of the atmosphere, which has hitherto been regarded as unassimilable by vegetables.

With regard to the quantity of the said two important articles of food in the atmosphere, it is important to observe that carbonic acid always exists there in such abundance that the plants can never fail of this. On the other hand, nitrogen in the form of ammonia and nitric acid occurs but in limited quantities. At the same time, the most recent researches have shown, that with the rain alone which fell in one year in the neighbourhood of Paris, 18 or 20 lbs. of nitrogen in easily digestible combinations of this kind, were received by 1 acre of land, which would equal the nitrogen of 1 cwt. of guano, and would suffice to provide about 4000 lbs. of dried fir-wood, or 2300 lbs. of dried beech-wood with the requisite amount of nitrogen.

As to the substances to which the enrichment of forest

Y

soil is to be ascribed, the statements already made can leave no doubt that they are those producing humus, and above all nitrogen. With this agrees moreover the experience of the forester, that those timber-trees in particular which have dense foliage and flourish in close proximity, thus especially beeches, firs, pines and the like, improve the soil in ordinary forest-culture; as also the foresters' rules, that the places where wood has been felled, or larger open spaces, must be brought into shade again as soon as possible, by planting; that a wood too openly planted had better be wholly felled and its cultivation recommenced, to oppose its deterioration, and restore a close growth of the trees; that, above all things, the covering of humus must be preserved, &c.

If a forest is well-covered, or if the same is effected by an abundance of underwood, the soil beneath is secured by the overshadowing foliage both from the immediate action of the sun and that of the wind; hence it will be far less heated and dried up it will be likewise incomparably less exposed than unshaded soil to extremes of weather, the circulation of air in its pores, and also the daily alternation between moisture and drought. In consequence of these favourable circumstances of growth, a more vigorous vegetation is produced in it, both in the timber itself and in the covering of herbage, moss, &c. of the soil beneath; thus there are plenty of collectors not only to absorb and keep the substances produced by decomposition, instead of letting them volatilize, but capable of abstracting nourishment in a greater degree from the atmosphere than a poor vegetation. As a result of this more vigorous vegetation, more refuse is produced, which, provided it is kept moist, is converted into fresh humus in the soil.

In meadows, where the grass crop is annually removed, an enrichment can only be expected when they are in damp situation or are manured or irrigated. Meadows in drier localities, and mountain meadows, to which no further addition of food is given either by manuring or irrigation, and where a yearly yield of some 18 to 24 cwt. of hay and aftermath is given per acre, gradually diminish in productiveness, as is testified by numerous complaints from N. America, Belgium, England, France and Switzerland. This amount of annual yield contains at least from 16 to 20 lbs. of ni