462 



THE FARMERS REGISTER. 



culture and the continued srowlli of plants, the 

 humus in the soil may even increase. 



" It is certain that the f;iimniy and resinous excre- 

 ments observed by Maaiire-Fiincep cou\d not have 

 been contained in the soil; and as we know that the 

 carbon of a soil is not diminished by culture, but, on 

 the contrary, increased, we must conclude, that all 

 excreirients which contain carbon must be formed 

 from the food obtained by plants from tlie atmosphere." 



" Both views [of the excreting; action of the 

 roots of plants] explain how it happens that after 

 corn, corn cannot be raised with advanfaj^e, nor alter 

 peas, peiis ; but they do not explain how a tield is 

 improved by lying fallow, and this in proportion to 

 the care iviih which it is tilled and kept free from veeds ; 

 nor do they show how a soil gains carbonaceous mat- 

 ter by the cultivation of certain plants, such as lucerne 

 and esparsette. 



" Theoretical considerations on the process of nutri- 

 tion, as well as the experience of all agriculturists, so 

 beautifully illustrated by the experiments oi' Ma caire- 

 Princep, leave no doubt that substances are excreted 

 from the roots ot plants, and that these matters form 

 the means by which the carbon received from humus 

 in The early period of their growth, is restored to the 

 soil."— (pp. 210, 211.) 



"Each of these [successive crops of] plants, during its 

 growth, returns to the soil a certain quantity of sub- 

 stances containing carbon, which are gradually con- 

 verted into humus, and are for the most part equivalent 

 to as much carbon as the plants had formerly extracted 

 from the soil in the state of carbonic acid." — (p. 216.) 



The author endeavor?: to prove his position, 

 that humus turnishes no Ibod to plants directly, 

 or oiherwise than by evoiviiig carbonic acid, by 

 several infrenious iirithnietical calculations, Ibund- 

 ed on the chemical proportions of the diderent sub- 

 stances in question. 'Mius. taking as data the 

 slight solubiiuy ol humic acid, (us ariifii'ially pro"- 

 duced by chemists,) he infers thai all the known 

 quaniity of rain, that lalls on an acre, could not 

 possibly dissolve enouiih humic acid to furnish 

 the carbon contained in the vegetable growth. 

 He shows, by the like kmd ofcalculation, Ibiind- 

 ed on the iime am) o'her substances lound in the 

 ashes of plants, wi:h which humic acid migHt 

 have (brnied humates and thus entered ihe plants, 

 that such sup[)lies are necessarily so small as to 

 make good his f)osiMon. But this mode of calcu- 

 lation, or reasoning, is altcgether in.idmissible — 

 and if admitted, would lead to the rncsi absurd 

 conse(]uences. For exan)ple- ii has been calcu- 

 lated (by Dundonald) that all the lime taken up 

 by the growth of an acre i[i a year does not ex- 

 ceed 80 pounds in the l()rm of caibonate. Now 

 it would be as legitimate a d duciion Irom this 

 (act, as are the arithmetical deductions of Liel)ig, 

 that 80 pounds of carbonate of lime, equally and 

 thoroughly diffused, would be enough to manure 

 an acre lor one crop, and that any increase ol" 

 quantity would be in excess. Yet we know that 

 10 times 80 pounds would scarcely be perceptible 

 in effect, and that 50 or 100 times as rpuch would 

 give no excess. 



Again — by using ihe like data and mode of 

 calculation, it might be shown by the chemical 

 analysis of the products, that all the Ibod of 

 plains derivable from a ceriain soil in one year, 

 upon any particular theory of nutrition, did not 

 exceed the quaniity that 20 loads (lor example) 

 of putrescent manure would supply. Yet the 

 vegetable matters, decomposed or in the course of 

 decomposition, previously in the soil, might have 



amounted to 40 loads; and yet not only would 

 the 20 loads applied be not in excess, and there- 

 lore useless, but twice or thrice as much would 

 have been siill n)ore beneficial. According lo the 

 calculation, the addition of manure, in any quan- 

 'iiy, ought *o be superfluous, and therefore useless. 



'I'he author also endeavors to maintain his 

 ground by the assumed lact, that culiivated 

 lands, from which crops are taken oil, and no mi(- 

 ficient return made, still increase in their siock of 

 carbon, notwithstanding the removal of it in the 

 crops. It is thus he sjieaks : 



" Let us now inquire whence the grass in a meadow, 

 or the wood in a forest, receives its carbon, since there 

 no manure, — no carbon, — has been given to it as 

 nourishment.' and how it happens, that the soil, thus 

 exhausted, instead of becoming poorer, becomes every 

 year richei in this element? 



" A ceitain quantity of carbon is taken every year 

 from the forest or meadow, in the form of wood or 

 hay, and, in spite of this, the quantity of carbon in the 

 soil augments; it becomes richer in humus. 



" It is said, tint in fields and orchards all the carbon 

 which may hdve been taken away, as herbs, as straw, 

 as seeds, or as fruit, is replaceci by means of manure ; 

 and yei; this soil produces no more carbon than that of 

 the tbrest or meadow where it is never replaced. It 

 cannot be conceived that the laws for the nutrition of 

 plants are changed by culture, — that the sources of 

 carbon for fruit or grain, and tor grass or trees, are 

 diiferent. 



" It is not denied that manure exercises an influence 

 upon the developement of plants; but it may be 

 affirmed with positive certainty, that it neither serves 

 lor the production of the carbon, nor has any influ- 

 ence upon it, because we find that the quantity of 

 carbon produced by manuied lands is not greater 

 than that yielded by lands which are not manured. 

 The discussion as to the manner in which manure 

 acts has nothing to do witli the present question, which 

 is the origin of the carbon. The carbon must be de- 

 rived from other sources ; and as the soil does not 

 yield it, it can only be extracted from the atmosphere." 

 — (pp. 68, C9.) 



Now, in the first place, it is not correct to say 

 that land receives " no manure," because foreign 

 manure is not brought and applied to it. A forest 

 or a meadoiv, though yielding lor removal part of 

 the produce yearly, yet, lioni the [)oriion left lo 

 lall and roi, may receive more carbon than is taken 

 away. For so much carl.'on is certainly derived 

 Irom the aimospiiere throui_'h the leaves of grow- 

 ing plan's, (according lo 'every different theory,) 

 that mere than half ihe whole products may be 

 taken away, and the other half may supply as 

 much humus and carhon, or perhaps even cause 

 an increase oi both. But if 'he draught upon the 

 land he carried beyond the amount of the sup[ilv, 

 the stock of humus (and of productive power) 

 will be reiluced in proportion. Ol this result, how- 

 ever rare in Germany, and on all well-regulated 

 farms, Prolessor Liebig could have thousands ol" 

 prools ou the severely cropped lands ol this coun- 

 try. We have also known (orest land to be much 

 reduced in productive power, even belbre being 

 cleared for cultivation, by its being partially and 

 continually robbed of its wood lor fuel, during 

 many years previously. 



But however we may differ as to the immediate 

 source, or mode of supply of carbon to plants, 

 eitl'.er theory will teach that the supply is un- 

 bounded. The atmosphere contains about one 

 per cent, ol" carbonic acid gas, which offers an 



