LIEBIG'S LETTERS ON MODERN AGRICULTURE.*

Tux subject of these letters has been a matter of controversy for some years between Liebig and many experimental agriculturists and writers on agriculture. The real point at issue lies in a nut- shell. Plants are composed of two elements, one of which is capa- ble of being thrown off by combustion, and consists fundamentally of carbon and nitrogen. The other is only reducible to an ash and consists of mineral constituents ; the word mineral not being used in the popular sense, but meaning phosphoric acid, potash, glide acid, &c. Liebig affirms that it is not sufficient to apply carbonaceous or nitrogenous elements to the soil ; you must re- store the mineral substances you remove. This last the practical agriculturists deny. They maintain that the soil itself contains sufficient of the mineral constituents to answer all demands ; you need only furnish the carbonaceous and nitrogenous elements. The great chemist does not altogether neglect experiment. In fact, as the readers of his " Principles " f may remember, he im- proved some land, and in his own opinion established his theory by practical proof ; but at a loss of nearly 7001., that being the difference between the costs of his experiment and the increased value of his ten acres. Strictly speaking his argu- ments in these Letters are mainly logical. They are cogent enough, if facts do not impugn them ; for it is self evident that if we remove an ingredient, essential to an effect, and do not restore it, the effect cannot be reproduced, or not so completely. And though his arguments are numerous and various they substantially rest upon that proposition. There are also reasonings from expe- riments, but as these have mostly been made upon a very limited scale, and cannot in any way be said to meet the infinite variety of soils, much less the mysteries connected with natural opera- tions both in the earth or the atmosphere, they can hardly be held so conclusive as those of the practical men. The most remarkable of these are by Mr. Lawes, who during a seven years' course on ap- portioned plots, without manure, with farm yard manure, and with various artificial manures, found very little difference between the produce from no manure and the artificial manures, while the farm yard manure produced a crop about one half greater than the others. Agriculturists likewise adduce numerous experiments and " general experience," all pointing in the same direction. Liebig's reply or rather objection that special circumstances of soil, &c. operated in these cases, would invalidate all agricultural experi- • Letters au Modern Agriculture. By Baron Von Liebig. Edited by John

Bluth, M.D., Professor of Chemistry Queen's College, Cork. Published by Walton and 31 aberley.

t Spectator for 1835, page 473. ments ; for no man can ever be certain but that special or occult causes may be operative in earth or air. His argument that farm- yard manure does contain mineral constituents, and may restore all that the crop has removed, is valid to the extent of the amount of the minerals, whatever that may be. The assertion that the soil may be so rich in mineral constituents, that it may go on producing for years without exhaustion, but will finally reach a state of utter barrenness, rather assumes the point at issue. If true, it is important in the last degree ; and that it is true the Baron fre- quently affirms. He looks upon high farming with apprehensive eyes. Improved implements that open the soil to the sun and air, and facilitate the free percolation of the water, and stimu- lating manures, as ammonia, which enable the earth to yield up its nutritive qualities to plants with greater readiness, as the roots can extend through a greater space, yield, he admits, muoh larger orops, and furnish a greater profit to individual cultiva- tors ; but at what a future loss ! Nay, the Baron maintains that in Germany the day of exhaustion has arrived, if it has not, as he seems to think, in England ; while in America much land in the older States has been abandoned, as we knew before. "It is asserted that the present system of husbandry yields greater crops, and produces more corn and meat, with more profit, on the same area than formerly. I will not, at present, contest this point, and therefore it is not now my object to attack this system, but rather to discuss the question, whether or not it is a rational one. If the large crops are a consequence of a mode of management by which the ground must gradually lose the condi- tions of its fertility, by which it must be impoverished and exhausted, then such a system is not rational, though it enrich the individual who obtains

these high returns. • • •

"In the seventeenth and the beginning of the eighteenth century, the culture of the vine was still flourishing in countless places in Germany; fields upon fields were then occupied by vineyards where the grape now no longer grows ; the large tithe-cellars alone, which still continue to exist in many places, give evidence of the immense extent of the vine culture in bygone days. With the vineyards the spoliation system of cultivation sooner produced its results; for vineyards produce no manure, and as the corn-growers found that the cultivation of their own fields stood in the ut- most need of all their manure, the culture of the vine necessarily died out,

like the flame of a lamp for want of a supply of oil. • • •

" All the ways and means which so marvellously tended towards the end of last century to increase the productiveness of the land, are at present re- sorted to in vain ; they fail to produce their former effect. The application of gypsum to the soil now makes the clover only more watery, without in- creasing the crop; land treated with marl is more unproductive than before. Were it not for the manure which the trees of the forest yield in many countries, the culture of the cereals would, in many former fertile districts, long since have come to an end, like that of the vine. The agriculturist in these parts now despoils the woods, as he formerly despoiled his fields, and he will continue this new system of depredation as long as it will answer. If you will grow clover, and will strictly follow my directions,' said the good Schubert to the peasants of his time, you will have ample cause for rejoicing and for praising the Lord out of the fulness of your heart for his rich blessing'. But bear in mind one rule, which I charge you now once for all to follow ; never grow clover it the'expense of corn, but grow it only in fallow, that it may cost you nothing—in other words, give up the prac- tice of letting a field lie fallow.' At that time there was no other system of husbandry known but the so-called three-fields-system,' or system of trien- nial rotation. In twelve years cereals were grown eight times in a field, and clover four times. Where are those glorious days when the same field yielded in three years two crops of corn and one of clover into the bargain ? Nowadays high farming produces in twelve years only six corn crops. In Mecklenburg good land produces only fo•ur oorn crops in nine• years.

• •

"A distinguished American economist, Carey, assures me that accurate statistical inquiries instituted in 1860 by the Times Commissioner have shown that England at that time produced actually 2,000,000 quarters of corn less than in 1774, according to Arthur Young. I will not venture to guarantee this fact, which if true, would certainly look very significant.

• • " In the United States, distances of hundreds and thousands of miles se- parate the places where the corn is grown from the markets ; the conse- quence of this may be seen in the fact that the soil is almost everywhere exhausted, and that the prosperity of the country is declining, instead of increasing.

" The rate at which this decline is progressing has lately been shown by a distinguished agriculturist, from whom we learn, ' That the phosphoric acid and the potash taken annually away from the fields, without any com- pensation worth mentioning being made to them, are at the current price of the market worth twenty million dollars ; that the ash-constituent of 600,000,000 bushels of corn are annually carried away from the land with- out any material restoration of them; that the entire annual waste of the mineral constituents of corn is equal to 1,520,000,000.bushels of corn.

• • •

" In New York, where the average yield of wheat was from 25 to 30 bushels eighty years ago, it is now only 12 bushels ; Indian corn gives only 25 bushels. In Ohio, a State which eighty years ago was still a wilderness, the average yield of wheat is under 12 bushels, and is decreasing instead of increasing. In Virginia, there is an extensive tract of land, once the rich- est in the State, which now produces only an average yield of wheat of less than 7 bushels; whilst in North Carolina land is cultivated which produces little more than the same yield of Indian corn. " In Virginia and Kentucky, tobacco was grown until the soil was com- pletely exhausted, and had to be abandoned ; and in the cotton districts we meet with a state of exhaustion unexampled in the world, for the shortness of the time in which it has been brought about."

Nor is this exhaustion confined to the modern world. It was one of the causes which conduced to ruin the Roman Empire; the writers of that epoch, Cato, Colnmella, and others, giving the same kind of advice as that of the practical agriculturists of our day, only better expressed. " All these rules [quoted from the classics] had, as history tells us, only a temporary effect ; they hastened the decay of Roman agriculture; and the small farmer ultimately found that he had exhausted all his expedients to keep his fields fruitful, and reap remunerative crops from them. Even in Columella's time, the produce of' the land was only fourfold. The fields fell into the hands of the large landed proprietors, who, by employing a multi- tude of slaves, were for a time enabled to obtain ' the largest crops at the

least expenditure of manure.' • •

" The sewers of the immense metropolis of the Ancient World, rguwhifeeed in the course of centuries, the prosperity of the Roman peasant : a d the.fields of the latter woldtfnelonger yield the means of feeding her popu- lation, these same sewers devoured the wealth: f Sicily, Sardinia, and the fertile lands on the coast of Africa."

• The remedy for all this the author considers to lie in fully re- storing to the fields, iu the form of manure, the constituents taken

from them, in the shape ' ape of grain and flesh especially. In earlier states of society when people were scattered over a country and small farmers were more numerous, this was done with less diffi- culty than now, when people [increased in number] are gathered into large towns, to which a few great agriculturists sendtheir corn, cattle, and other beasts, but do not, and indeed under existing circumstances cannot bring it back. Guano has been a wonderful aid ; but guano is exhaustible ; already it has doubled in price ; America, which at first slighted it, is now using it.: and political circumstances might impede its free importation. Sewerage is the resource to which Liebig looks, though he admits there seems a difficulty in converting it to use in London, and some English ex- periments have not confirmed its theoretical value.

" The annual fluid and solid, excrements of a million inhabitants of large

cities (men, women, and children,) weigh in the dry pulverulent state forty- five million pounds ; in which are contained 10,300,000 pounds of mineral anbstances, mostly ash-constituents of bread and meat, (not including five million pounds weight of bones of the slaughtered cattle, &c., nor the mine- ral substances in the evacuation of borsea, &c.) These human excrements alone contain 4,680,000. pounds of phosphates.

" This enormous dram of these matters from the land to towns has been going on for centuries, and is still going on year after year, without any part of the mineral elements thus removed from the land ever being restored to it; a very small proportion only is turned to account in the garden and fields in the more immediate vicinity of towns. " It is perfectly absurd to supposeothat the loss of these matters which are so essential to the productiveness of a soil should have had no influence upon the amount of its produce."

In point of consistent logic and scientific views, the Baron has the advantage over his opponents, at least over those whom he quotes to covertly ridicule ; but there is throughout a tinge of angry animus, not quite appropriate to scientific discussion ; and we do not see that he has established his case, though he shows it to be highly probable. He has, however, called the attention of the world to one of the most important questions that can con- cern it ; and even should his theory remain torpid till a sad ex- perience confirms it, the knowledge of the remedy will be present to men's minds. The " Letters," it may be added, are not wholly controversial, but contain many observations on subjects con- nected with agriculture ; and a most capital exposition of the laws of vegetation.