March, 1842. 



THE FARMER'S MONTHLY VISITOR. 



43 



hydrogen, produces nrninonia. It is in the form 

 of ammonia, tiiat plants receive their nitro),'en. — 

 This ammonia is fm-iiished to the roots of the 

 plants by the decomposition of animal matter in 

 tlie soil,"and to their leaves by the effluvia arising 

 from decayed and decaying animal and vewtable 

 substances. This decay is continually going on, 

 and, together with the excrements of animals, 

 su|)plies the ammonia contained in the atmo- 

 sphere. Tliere are, indeed, some natural subter- 

 ranean sources of ammonia, connected with vol- 

 canic action ; and ammonia is found in many 

 springs, which, Liebig supposes, derive it wholly 

 from the atmosphere. The principal part of the 

 nitrogen, which is found in plants, is, in his opin- 

 ion, obtained in the form of ammonia in rain wa 

 ter. Though it appears, that it as been discover- 

 ed by others, that rain water contains ammonia, 

 yet it is believed that Liebig has been the first to 

 annoimce the fact. He goes on to show, by the 

 elements made use of in a former calculation, that 

 by means of the rain falling annually upon 40,- 

 000 square feet of soil, the field must receive 80 

 lbs. of ammonia, or 6.5 lbs. of nitrogen, which is 

 more nitrogen than is contained in the amount of 

 crops usually produced upon such a surface. — 

 The experiments made to ascertain the presence 

 ofammonia in rain water, are decisive, and this 

 interesting (act may be considered as now estab- 

 lished. He likewise detected ammonia in the 

 juices of the maple and the birch tree; this being 

 obtained remote from any house, was evidently 

 derived from tlie atmosphere. 



There are facts connected with cultivation, and 

 allowing the effect of different manures upon the 

 quality of the products, which are extremely cu- 

 rious. Different wheats are found to contain very 

 different proportions of gluten, of which nitrogen 

 forms an important constituent. Some French 

 wheat was found to contain 12.5 per cent of glu- 

 ten, while Bavarian (contained 24 per cent. Davy 

 obtained 19 per cent, from winter, and 24 from 

 sununer, wheat. Sicilian wheat afforded 21 per 

 cent.; Barbary vvlieat, 29; Alsace, 17.3; wheat 

 grown in the Jardin des Pinnies 26.7, and winter 

 wheat .3.3-3 per cent. In regard to these differ- 

 ences, Liebig remarks: 



"An increase of animal manure gives rise not 

 only to an increase in the number of seeds, but 

 also to a most remarkable difference in iIk- pro- 

 portion of gluten which they contain. Animal 

 manure acts only by the formation of ammonia. 

 One himdred parts of wheat, grown on a soil ma- 

 nured with cow-dung (a manure containing tli.-^ 

 smallest quantity of nitrogen,) affording only 

 11.95 parts of gluten, and 64.34 partsof amylin or 

 starch ; whilst the same quantity, grown on a soil 

 manured with human urine, yielded the maxi- 

 mum of gluten, namel}', 35.1 per cent. Piitrified 

 urine contains nitrogen in the forms of carbonate, 

 phosphate, and lactate of ammonia ; and in no 

 otlier form ihan that of ammoniacal salts." — p. 

 136. 



As illustrative of the value ofammonia in veg- 

 elation, Liebig refers to guano. This is the ex- 

 crement of sea-birds, and fomid in large quanti- 

 ties on several islands in the South Sea. Tlie el- 

 fect of this manure is understood to he most pow- 

 erful. It renders the soils, which consist of clay 

 and sand, and contain, as is represented, no or- 

 ganic matter, highly fertile. This manure is com- 

 posed principally of suits ofammonia, and a few 

 earthy salts. 



LieVig, if his theory be well founded, has solv- 

 ed the secrets of the operation of gypsum. It has 

 been supposed, that gypsum acteil upon plants as 

 a stimulus, or like ardent spirits upon animals. — 

 •But plants are not animals. They have no nerves, 

 which may be tightly drawn or relaxed ; and such 

 suppositions, which serve only to betray our ig- 

 norance, are without foundation. No siibstance 

 can cause the leaves of plants to appropriate an 

 excess of carbon from the atmos])here, when the 

 other constituents of the plants are wanting. — 

 The influence of gypsum is to fix the ammonia 

 which is brought into the soil, and preventing its 

 evaporation, give it out as the plants may receive 

 it. This efject is produced by the double decom- 

 ])osition of the carbonate ofammonia, and of the 

 gypsum or sulphate of lime, by which sulphate 

 ofammonia and carbonate of lime are tfjrmed. — 

 His notions on this subject, being the first satis- 

 factory attempt' at a solution of the mystery al- 

 ways cnuuected with the application of this ex- 



traordinary substance, are curious and interest 

 ing. 



"In order, (he says,) to form a conception of 

 the effect of gypsum, it may be sufficient to re- 

 mark, that 100 lbs. Hessiati of burned gypsum 

 fixes as much ammonia in the soil as 6,250 lbs. of 

 horses' urine would yield to it, even on the sup- 

 position that all the nitrogen of the urea and hip- 

 puric acid were absorbed by the platus without 

 the smallest loss, in the formof carbonate of am- 

 monia." — p. 143. 



He is equally original in his explanation of sev- 

 eral other facts. 



" The advantage of manuring fields with burn- 

 ed clay and the fertility of ferruginous soils, 

 which have been considered as facts so incom- 

 prehensible, may be e.xplained in any equally 

 simple manner. The oxides of iron and alumina 

 are distinguished from all other metallic oxides 

 by their power of forming solid compounds with 

 ammonia. Minerals containing alumina or oxide 

 of iron also possess in an eminent degree the 

 remarkable property of attracting ammonia from 

 the atmosphere and of retaining it." 



Powdered charcoal is another element which 

 powerfully absorbs ammonia ; and will take up 

 ninety times its volume of ammoniacal gas,which 

 it gives out upon being wet with water. Decay- 

 ed wood resembles charcoal in this property, ab- 

 sorbing seventy-two times its own volume. This 

 explains further the operation »f humus, which 

 supplies not only carbonic acid, but likewise 

 nitrogen, to the growing plants. 



Liebig concludes this chapter with a beautiful 

 reflection : 



" Carbonic acid, water and ammonia contain 

 the elements nece.ssary for the support of ani- 

 mals and vegetables. The same substances are 

 the ultimate products of the chemical process of 

 decay and putrification. All the innumerable 

 products of vitality resume, after death, the ori- 

 ginal form from which they sprang. And thus 

 death, — the complete dissolution of" an existing 

 generation, — becomes the source of life for a new 

 one." 



The next subject of discussion with Liebig re- 

 lates to the inorganic constituents of plants. — 

 These are potash, soda, lime, magnesia, oxide of 

 iron, manganese, silica, and other substances. 

 The plants cannot be perfected without them. 

 Alkalies of one kind may often be substituted for 

 those of another ; but they are always found in 

 equivalent proportions. These inorganic sub- 

 stances are admitted to the plants in combination 

 with some acid. They exist independently of 

 tlie plant, and are not the product of vital action. 

 They are fomul in different soils, and are the re- 

 sult of the decouiposition of various rocks. Pot- 

 ash is an important constituent of most felspars. 

 Some of tlie salts are evaporated in sea-water, 

 and in that way carried far into the interior, and 

 alter being spread upon the e;irth, are carried 

 down by the rains. They are returned to the soil 

 iu decayed vegetable and animal matter, and in 

 tiie excrements of animals. They are found in 

 the ashes of plants, in the form of carbonates; 

 and by careful analysis their amounts in differ- 

 ent cases have been accurately ascertained. The 

 amomitof alkaline substances required by plants 

 is very minute. But tiiat amount is i-equisite to 

 the perfection of the vegetation. It is easy to 

 conceive how small an amount is required in 

 ths soil, viW.n it is umlerstond that sea-water 

 contains only 1-12400 of its weight of carbonate 

 of lime, and yet that is sufficient for the forma- 

 tion of all the banks of coral in the ocean, and 

 the various shells of the marine animals. 



Having given this account of the constitur'nts 

 of plants', and the sourcos wlience they are de- 

 rived, Liebig proceeds to <liscuss the art of cul- 

 ture and tlie action of manures. I should he 

 glad to quote the whole of this chapter, but must 

 limit myself to a brief sketch. Humus is not 

 soluble in water; if it were, a great piart of it 

 would he carried off the giound by rains. Its 

 office is, by the presence of water to convert the 

 siu-rounding oxygen into carbonic acid, which 

 plants absorb, and then return to the soil a large 

 portion of carbonaceous matter, that thsy alistract 

 from the air, so that the liumus of tlie soil is not 

 diminished. The frequent ploughing of the soil, 

 so as to promote, by admitting the oxygen of the 

 air to the humus, the formation of carbonic acid, 

 the application of alkaline substances, and what- 

 ever tend-i, as T.ir^big (expresses it. to put the or- 



ganic matters of the soil into a state of oxidation, 

 increase the fertility of the soil. The oxygen 

 then assists in the formation of carbonic acid to 

 go to the nourishment of plants. 



Knowing the substances which go to form the 

 plants, the object of a wise agriculture will be to 

 supply thent, and to render them accessible to 

 the plants. Potash, the most common and im- 

 portant of the inorganic constituents of plants is 

 more universally and abundantly diffused over 

 the earth than any other alkaline substance. But 

 the alkalies, by continued cultivation, may be ex- 

 hausted, and the soil cease to be produclive 



This indicates the necessity of a fallow or rest' to 

 the soil, by which, under the operation of air and 

 moisture, a further disintegration of the rocks 

 may take place so as to furnish the necessary al- 

 kalies to the soil, or, without resting, they may 

 be artificially supplied. Plants themselves in 

 their decay return alkaline substances to the 

 earth ; and it is well ascertained that plants 

 themselves act powerfully in the disintegration of 

 rocks. 



Some crops may be repeated on the same soil 

 more frequently than others, because some con- 

 sume more of the alkalies than others. One 

 hundred parts of the stalks of wheat yield 15.5 

 parts of ashes. The same quantity of barley, 8.54 

 parts ; and of oats, only 4.42. The ashes of these 

 different plants are of the same description, but 

 it is obvious that the demands which they make 

 upon the soil must be difterent. 



The interchange of rotation crops and the ap- 

 plication of manures are materially connected 

 with this fact, and with another in "the habits of 

 plants, to which we shall refer. Plants of <|jfl%r- 

 ent kinds absorb or take up different substances, 

 from the soil ; and one kind therefore may flour- 

 ish, where another would fiiil. The same kinds 

 of plants cannot be cultivated in succession on 

 the same soil for any length of time without de- 

 clining iu productiveness. Some plants, as flax 

 for example, will not bear a repetition on the 

 same soil oftener than once in five years. It has 

 been supposed that plants themselves assimilate, 

 and consume in their growth, certain ingredients 

 in the soil necessary to the perfection of the plant, 

 which should not be repeated on the same ground 

 until this material is again supplied. But this is 

 not all. No artificial supply of any a.«certainable 

 ingredient can control this general law of the ne- 

 cessity of a change in the rotation, growing out 

 of other circumstances. Decandolle suggested, 

 and may be said to have established, anot7ier the- 

 ory, namely, that plants excrete from the loots 

 certain substances, which are innutritions or hurt- 

 ful to the same khid of plant in succession, but 

 which may serve us the food of other plants. But 

 there are difliculties, in respect to this subject, 

 upon which we cannot dwell, which Liebig's the- 

 ory solves with remarkable ability and ecpial rea- 

 sonableness. The exudations or excretions of 

 plants may be considered of two kinds. Plants, 

 as we have before said, have no selection in their 

 food, but take up with little discrimination what 

 is accessible to their organs of nutrition, and in a 

 condition to be absorbed. Tliey consequently 

 may take up many things, which "they can assim- 

 ilate but in part, or not ai all. These are exuded, 

 anrl inay serve as the food of other plants of a 

 difieieiu cliaracter. But there is another class 

 of excretions, or properly speaking, excrements, 

 which are purely the result of the vital action of 

 the [ilants, and which, in the form of gum or 

 otherwise, after having' served the purpose de- 

 signed in tlie iiutritiuii of tin; plants, pass off by 

 the afipioprialc oiirans into the soil. These, o"f 

 cours.', cannot serve as the food of the same 

 kind of plants, or oi' any other in their present 

 conilition ; and these fro to nssi-t in fliniiing the 

 liiimus of the soil. In Iht-ir iiiicIkuijciI condiiion, 

 these excrements ara |i."riiicioiis to the kind of 

 plants from which thi'V ucre discliargL'd, and, it 

 may be, to others; and after buconiing converted 

 into humus, under the operaiioii of air and 

 , the effects are the .same as those of 



After all, wirore tlie crops are ri'mnvrd finin 

 the soil in the iiirms of .■seeds, mors, .-un! ,'eaves, 

 the soil is of course deprived of nrwy of the 

 constituents requisite to a healthful and |iroduc- 

 tive vegeUition. The substances removed are 

 then to be supp!i<nl by maijiire. The seed of the 

 plant contains within itself the food, which it first 

 reqtiii-.'= hi order to the protru-iion of it-J radicles.- 



