LIEBIG'S PRINCIPLES OF AGRICULTURAL CKBMISTRL • WHEN Radcliffe was offended with

the conduct of his brethren, he used to threaten that he would leave behind him the whole art of physic written upon half a sheet of paper. Experiments by Mr. Lewes, with comments thereupon by Mr. Pusey and others, in opposition to the mineral theory—that is, the necessity of applying mineral constituents to the soil—have induced M. Liebig, not indeed to expound the art of agriculture on half a sheet of paper, but to exhibit the principles in a small compass. In fifty numbered propositions, contained in less than twenty pages, he lays down the laws which govern the growth of plants. In a cer- tain sense, however, the German chemist may be said to have outdone the English physician; for the whole fifty propositions are contained in and may be deduced from one propositicn, which is thus expressed—" The nutrition, the growth, and the develop- ment of a plant, depend on the assimilation of certain bodies, which act by virtue of their mass or substance." Of these, water is indispensable, both as a nutritive substance and as a solvent to enable the "mineral food" of plants to be received; as this can only be effected in a solvent state. The "atmospheric food" of plants, received through the leaves, consists of carbonic acid and ammonia. These two substances can also be drawn from the soil, of course if the soil contains them. The dispute between Liebig and his English and German impugners turns upon the questions of "ammonia" and "mineral food."

The most important physiological discovery of modern times is Liebig's principle that the nutritive functions cannot create, but only assimilate. The stomach of animals, and the roots of plants, which are a stomach turned inside out, can separate from the food those elements which are essential to life and growth ; but if the elements are not in the food, neither stomach nor roots nor the other nutritive organs can create them. And the truth of this view is generally received, though there are, we believe, dissentients. It follows as a logical conclusion, that if a succession of the same crops continually carries off from the soil the needful elements of nutrition without those elements being replaced, the soil must eventually become exhausted; the time in which this exhaustion takes place depends upon several circumstances, of which the rich- ness of the soil is a main thing. It is a theory of Liebig, that by annually replacing the elements annually removed, the same crops could be continued year after year. Experiments were tried in this country with artificial manures manufactured from his re- cipes; but the result was not suceessfuL Mr. Lawes does not seem to deny the principle of assimilation, or the general conclu- sions drawn from it ; but he conceives his experiments have set- tled that the theory of Liebig on "mineral manures" is of little value and have established the great value of ammonia. On wheat, for instance, he draws these conclusions-1. That the mineral constituents of wheat cannot by themselves increase the fertility of land ; 2. That the produce in grain and straw is rather proportional to the supply of ammonia.

The experiments made by Mr. Lawes extended over seven years. Their nature and general results may be shortly stated. He di- vided fourteen acres into a number of plots. One plot he did not manure at all; another he manured annually with stable manure ; to the other plots he applied different kinds and quantities of arti- ficial manures. The result of the seven years' experiments was, that the land manured with stable manure yielded a predate one half greater than that of the unmanured land; but there was little difference in the produce between the artificially manured plots and the plot which was unmanured. Liebig's mineral manure alone was in some degree superior to the rest. The reply to these ex- periments is perfectly clear and intelligible in statement; perhaps it is too much an affirmation to be satisfactory to opponents, though it may be true. The soil of Mr. Lewes, says Liebig, was already so rioh in mineral constituents that it could not beneficially re- ceive more under existing circumstances. For proof of this, he points to the power of the unmanured plot to produce large crops for so many years. The effect of the ammoniacal experiments, he explains thus. Ammonia is a stimulant enabling a greater pro- duce to be raised from the actual constituents of the soil, but ex- • Principles of Agricultural Chemistry. with special Reference to the late Re- searches made in England. By Justus von Liebig. Published by Walton and liaberly.

hausting the land. For example, you raise half as much again by doses of ammonia ; your soil will be exhausted in eight years in- stead of twelve years. Pure ammonia is besides too expensive for agricultural purposes in reference to profit.

" To seek to ascertain the effect of ammoniacal salts in the way Mr. Lawes has done, and to recommend the use of these salts for the cultivation of wheat, seems to me almost a mockery in the present state of agriculture ; for all the ammoniacal salts manufactured in Europe are not sufficient to supply the lands of even the kingdom of Saxony with these salts, in the quantities recommended by Mr. Lewes. It has been known for centuries, that nitro- geuized manures are useful for certain crops ; that the active mineral sub- stances become more efficacious by the addition of ammoniacal salts than without them, is a conclusion, as is proved by the quotations from my work, simply deduced from theory, to test which no experiments are necessary. But so to prepare the soil as to enable it to extract from the air, and the other sources offered to plants by nature, and to condense in its products a maximum of nitrogen,—this, indeed, is a problem worthy of scientific agriculture. " The results of Mr. Lewes have no value for his next-door neighbour ; nay, they have no value for himself ; for the recipe to which he CollIt's only applies to his own lands, and to them only in so far as experimented on, and only for a very limited number of years."

The arguments on Mr. Lawes's experiments and conclusions am carried on at considerable length, occupying indeed a large portion of the volume. They are mingled with remarks and expositions connected with the controversy ; some of them of much interest and utility, but the controversy itself is not admirable in its tone. M. Liebig seems sore with Messrs. Lewes and Pusey, and Dr. Gilbert, who chemically assisted Mr. Lewes, as well as with Wolff and other Germans, who pronounce the pure mineral theory " not confirmed by the practical experience of agriculturists." This feeling may not affect the cogency of the arguments, but it gives a touch of asperity to the manner. M. Liebig evidently likes to catch his antagonists tripping, even if the advantage to the argu- ment is not perfectly obvious.

Independently of the fifty propositions, there is a good deal of useful exposition connected with agricultural chemistry before the controversy begins. If we put aside the obvious causes of failure that may overtake agricultural operations,—as weather, insects, and the less perceptible causes that escape observation ; and if we assume that the land is brought into a proper physical condition by breaking up and draining,— since to have the food of vegetables in the soil is useless, if the soil be so hard that the roots cannot penetrate, or if stagnant water poisons the plants ; then it would seem from Liebig's principles, that good crops can be grown any- where, if the land is only supplied with sufficient " food " or ele- ments, according to the nature of the crop desired. This, in fact, was a main object of the various experiments made by farmers in England : but the failure of a new experiment undertaken by men who probably had not a discoverer's interest in the matter, and who might want the perception and dexterity necessary for the undertaking, does net prova much against a theory. There are always unforeseen difficulties in the practical introduction of a new principle, even when the speculator is a master of his invention and when the conditions are more under human control than agricul- tural operations ever can be. With a rather important qualifi- cation, which we will come to presently, Liebig made the experi- ment himself, and succeeded.

"During the years 1845 to 1849, I made a series of experiments on the action of the different mineral manures, on a considerable scale, on a piece of land of about ten English acres, which I purchased with this object from the town of Giessen. Previous experiments, which I had made in my garden in the town, had yielded no result. Whatever I did, or whatever I might add to the soil, I was unable to trace any perceptible effect from any of my mix- tures. The only cause which I could discover for this apparent want of effi- cacy was the composition of the soil of my garden, which, by previous culti- vation and manuring, had become in itself so rich in available mineral con- stituents, that the addition of a relatively insignificant quantity of these substances became, when compared with the amount already present in the soil, quite inappreciable. This induced me to purchase the land alluded to, a sand-pit to the East of the town, which I found to surpass all others in the whole surrounding district in its nearly complete barrenness for the ordinary cultivated crops. I do not believe that, in a whole year, there grew naturally on the whole ten acres as much grass or other fodder as would have sufficed for a single sheep. The soil is in part a light sand, in part it consists of more or less coarse quartz pebbles and thin strata of sand with some loam.

"I filled with the natural soil a number of flower-pots, in which I sowed wheat, barley, and red clover, and manured each with some single mineral manure. In none of these did the plants get beyond flowering. The land therefore was of the quality adapted to the object I had in view. "Messrs. Schwarzenberg and Co. of Ringkuhl, near Cassel, were so ob- liging as to prepare for me, in their soda-works, according to the prescrip- tions I gave them, a quantity of mineral manure, which was spread uni- formly over the land, except a portion used as a vineyard, on which there were about two thousand vine-stocks, each of which, on being planted, had a quarter of a pound of the manure mixed with the earth about its roots. On the different subdivisions of the land there were sown wheat, rye, bar- ley, clover, potatoes, turnips, maize, topinambour; some small lots had saw- dust added to the mineral manure, one had only stable manure, and another equal parts of stable manure and mineral manure. With the exception of the stable manure used for these two lots, no ammoniacal manure, and no animal substance, was applied to any part of the field. One lot had several cart-loads of forest Boil from a neighbouring wood; another had a mixture of forest soil and mineral manure.

"Several of the meet distinguished agriculturists of the district, and among them Herr von Fernhaber, thought that I could not succeed in grow- ing wheat or clover on this soil ; and the opinions of these gentlemen with regard to my enterprise are still fresh in my remembrance. I had calculated only on a very small produce in the first year, as the soil had never before been under cultivation : but however moderate, nay poor, the harvest was, it yet surpassed that which I had anticipated. It was indispensable that some years should elapse before the constituents of the manure could be rendered soluble, and thus diffused throughout the soil. The barley was better on the lot manured with forest soil and mineral manure than on the other : on the lot which had been manured with sawdust and mine7.1 ma- nure the plants were also larger and stronger; the lot with stable manure and mineral manure yielded a crop of wheat as rich as that on any of the

best of the neighbouring fields. It was the effect of the sawdust, and of the organic matter (humus) in the forest soil, and in the stable manure, which first opened my eyes to the true action of humus and decaying organic matter in the soil; and my previous notions on the subject were thus cor- rected and enlarged. • • • "It was only after the lapse of four years that the mineral constituents added to the soil gradually came into action ; and the land will, as may easily be foreseen, retain its present fertility, if a quantity of these mineral constituents equal to that contained in the crops sold off the land be an- nually restored to it.

" The action of the several ingredients of the manure showed itself in a most striking manner, in many cases so as to excite astonishment. The de- ficiency or excess of phosphate of lime and of the alkalies for root crops, of the alkaline earths for clover, and of silicate of potash for the cereal crops, could be distinctly traced in their growth. The experimental lots were as the writing on the pages of a book—intelligible even to the uninitiated.

"I have every reason to believe that by means of the organic refuse left on the land from the crops removed, (stubble, roots, leaves, bto.,) in conse- quence of their decay, and of the action of the carbonic acid formed from their carbonaceous constituents, mineral food -for plants was extracted from the original soil, and rendered available, which had formerly been utterly without effect."

After the lapse of the four years the land was sold; and now comes the practical qualification.

"My experiments, which cost me an outlay of 8000 florins, (about 670/.,) that being the difference between the whole expenditure and the price received for the land, prove, no doubt, that the fertilizing of barren land, if its barrenness arise from a deficiency of the necessary constituents, and not merely from a bad physical condition, renders necessary an expenditure which exceeds the price of an equal extent of the most fertile land.'

Some years since, Boussingault laid down the axiom that at- tempts to improve soils by changing their nature, by carting sand to clay or clay to sand, involves an expense greater than the value of the improvement. He holds that the only mode of profitably improving is by the best cultivation which the nature of the soil admits : this method always pays, and permanently improves. If M. Liebig's experiments were not made too lavishly and hurriedly, it would seem that land beyond a certain degree of barrenness, or, in his language, with "a deficiency of the necessary constituents," must altogether be excluded from the category of practical im- provements. Where the barrenness arises from the presence of noxious substances or the want of water, as at certain places of the Crimea mentioned by Koch, attempts at improvement are hope- less. When it is mere "deficiency," it is probable that time and homely cultivation,•may render the improvement profitable.