hand, that the soil does not contain any excess of them, since if this were the case, an increase of the quantity of them in the soil would be a matter of indifference to the plants growing upon this, and would produce no effect.

d. Lastly, I will mention one more fact, which is to me especially convincing, because it rests on the experience of ages, namely the fact, that the manures by which the fertility of cultivated soil has been maintained for centuries, almost all agree in containing nitrogen and phosphoric acid as their principal constituents (with only smaller quantities of potash, lime, &c.). The solid excrements of domestic animals formed the sole manure of the farming of earlier times, and make up the greatest part now; these two most important constituents are-nitrogen and phosphoric acid. Guano, which the Peruvians have used for 300 years and more as the sole manure of their fields, without diminution of the productiveness of them, likewise contains as powerful ingredients,--nitrogen and phosphoric acid. A traveller, Prof. Pöppig, who lived a long time in South America, speaks of guano, in regard to this fact, to the following effect :- "The results of this manure in Peru are undoubtedly great; we may even assume that there, where the manure of cows and horses is not collected at all, and the method of agriculture in this country does not even permit the latter to be done, all sandy and exclusively artificially irrigated land of the coast district would be as sterile, without guano, as that renowned desert, surpassing Sahara in uninhabitableness, which spreads out in the south of Peru, under the name of the Desierto de Atacama." What is true of guano, applies also to bone-dust and rape-cake. The soil of the Saxon farms, where stockkeeping has been done away and the fields have been from eight to fourteen years manured either with bone-dust alone, or with guano and bone-dust, is at present in no way exhausted or otherwise deteriorated, but rather, as I lately have seen to my great satisfaction, in all cases where it is well-tilled and manured, has annually become more powerful and richer.

The following summary will show what preponderating quantities of these two substances, nitrogen and phosphoric acid exist in the manures in question :-

One morgen of land receives in one manuring, about

If, as experience proves, we can work permanently with these manures against impoverishment of the soil, and even bring it into a higher condition, it will not be doubted that this effect is to be ascribed to the nitrogen and phosphoric acid. If, further, it is wished to decide between these two, nitrogen is to be placed unhesitatingly in the first line, phosphoric acid in the second, and potash in the third, &c. The fact that lime is given to the soil to some extent in the said manures, is of quite subordinate importance, seeing the facility with which lime may be added directly to it.

XVIII. IMPOVERISHMENT OR EXHAUSTION OF SOIL.

ALWAYS paying and never receiving leads at last to bankruptcy, and of course the more rapidly in proportion to the amount of the payments. Our soil is in the same case: if it must always give out without obtaining a return, it will gradually grow poorer and at length completely bankrupt. The growth of plants and their full development, require certain ingredients in the soil and certain quantities of them, just as we ourselves also absolutely require particular food and particular quantities of it to support our bodies. If these are diminished in quantity in the soil, the pro

ductiveness of this decreases; if they all go, its productiveness ceases entirely. To restore this, only one means exists; we must re-convey to the soil, from other sources, those ma

terials in which it is deficient.

Most frequently, however, it is not a total deficiency of one or more ingredients which renders a soil unproductive, but a want of the proper form and consistence of them. They must be soluble and digestible by the plants, to be of any service to them. Continued cultivation may readily lead to the exhaustion of the store of soluble materials in the soil; and when this is the case, the growth of the plants must likewise halt, or even cease, although perhaps a larger store of the same food may still exist, but in an insoluble form, in the soil. Such soil may be restored to productiveness, not only by the direct addition of the deficient soluble ingredients, but by a second, much slower method, namely by "rest" or "fallow," as during this repose the weathering and decomposition produce a fresh quantity of soluble food, which suffices sometimes for one, sometimes for several crops.

When nature is left to herself we see no decrease in the power of the soil, rather a gradual increase. We even perceive such an increase in the soil of forests, although we remove at intervals of 50 or 100 years what has grown up out of it. But we observe a distinct impoverishment of soil wherever man comes with his troubles, removing the refuse, felling timber without planting, sowing and reaping without manuring, &c., in every case, indeed, where the soil is compelled to give up more than it receives.

We have a frightful example of the last kind in the Agriculture of North America, as is most distinctly proved by an official report recently published by the Senate at Washington. Although I doubt not that we could find examples of the same kind nearer home, I shall be content with this, and draw out a few particulars from it, which I think will speak more plainly and convincingly than the most exact theoretiIcal evidence could.

The State of New York possesses about 30 millions of acres of cultivated land, which is farmed as field, meadow and pasture. The number of agricultural labourers amounts to about 500,000 persons, so that there is an average of but one labourer to 60 acres of land. It may be regarded as

abundantly proved, that 300,000 of these farmers practise an exhaustive agriculture, a kind of robbing-cultivation, by which the soil annually becomes poorer,-120,000 a system which tolerably maintains the productiveness of the soil,and therefore that only about 80,000 so farm that they can expect a gradual enrichment of their soil. Looking at the superficies, it may be assumed that of the 30 millions of acres of cultivated land, the productiveness diminishes in ths, remains even in ths, and increases only in th.

The

The last, that is only 1th part of the whole, is in the possession of farmers who read agricultural journals and frequent agricultural meetings, who manure their fields and cultivate according to a rational succession of crops. intermediate section comprehends those farmers who do not read, study, reflect and test themselves, but endeavour empirically to imitate what appears to them good and ascertained in the hands of their more intelligent neighbours. The first section, including two-thirds, lastly, is in the hands of agricultural freebooters and extortioners, who treat the virgin soil in the manner of an inexhaustible gold mine; that is, cultivate and use it up, without dreaming of a return in the shape of manure, as long as the crop will repay the outlay. When this epoch is past, they leave it and turn to another district, to recommence this vampire-work there.

The following figures will show how greatly this prevailing exhaustive mode of culture has diminished the general product. The same soil of good districts of New York, which 75 or 80 years ago yielded a produce of wheat of 12 to 15 bushels per acre, now yields in Ransselaer only 4 or 5, in Albany and West Chester 3 to 4, in Columbia 3, and in Duchess County only 2 bushels. A similar diminution of the fertility is likewise observed in the grass-land prairies, the hay-crops of which become smaller every year.

The prospect is not much better in the other States of North America. In the thirteen old States, especially in Virginia, Maryland, Carolina and Georgia, which have mostly a light, sandy soil, immeasurable tracts now lie unproductive and deserted, which yielded good crops forty or fifty years ago.*

The causes of the impoverishment of the soil named in the Report are,-a, in the grass-lands, the constant mowing for hay which is removed, without any return being made

to the soil, either by manuring or irrigation; b, in the arable land, by the uninterrupted cultivation of tobacco, cotton, sugar-cane, maize and wheat, without alternation and without manure. In a few districts only is fallowing practised, or occasionally variation with a leafy fodder-plant, mostly however without manuring. Here the productive power of the soil diminishes certainly more slowly, but nevertheless it does become smaller, and the final result of this mode of farming will and must in like manner be sterility, although this does not supervene until a later period.

The proposals for improvement may be passed over here, since they are self-evident. But I must quote the conclusion of the Report, because it shows how correctly the root of the evil has been perceived. It says,-" Before however the soil will be improved, the farmer must be improved, and this can only be effected solidly and quickly by science. A radical and universal amelioration of the melancholy condition can only be hoped for, when the farmer has acquired a clear insight into the natural laws and forces, that is, when he adds rational theory' to his practical routine."

In this theme too, to run less danger of falling into error, I set up the experience of practice once more as text, and subjoin the theoretical conjectures as explanations and illustrations of this.

Experience of Impoverishment of Soil in Forestry.

The facts of experience in this field appear to me of especial importance for the theory of the exhaustion of soils, in the first place, because there are here many more simple conditions than in agriculture, since they are free from the complex influences exercised by the tillage of the soil, the manuring, the diversity of the plants cultivated, and of the methods and systems of cultivation followed; secondly, because the experience extends over longer periods of time; and lastly, because these exhibit a far greater internal agreement than agricultural experience. The conclusions to be drawn from this experience for the explanation of the impoverishment of soil, will be brought together further on. The facts themselves are somewhat as follows:

1. The soil of forests becomes waste and impoverished if it remains uncultivated after it has been completely stripped