1835.] 



FARMERS' REGISTER. 



387 



intimate composition of these substances is not 

 jet perfectly known, their elements may exist in 

 the atmosphere, or even in the soil, among the 

 substances which compose them. 



Neither can it be said that these salts may be 

 derived from the atomic dust, which floats in the 

 air; for this dust is composed of fragments organic 

 and inorganic, carried especially to the plants 

 themselves, and then, in estimating this atomic 

 matter at the most, we will scarcely find in it the 

 hundredth part of the saline substances contained 

 in the vegetable mass produced. We ought then 

 to conclude that the saline substances of plants 

 are formed by the powers of vegetation, or of the 

 soil. 



31. In like manner as with the saline principles, 

 the lime and the phosphates of ashes ought to be 

 due to the same ibrees, whether that the roots 

 take up their unperceived elements in the soil, or 

 that the leaves gather them in the atmosphere. 

 This consequence results evidently from this fact 

 — that plants grown in soils, of which the analy- 

 sis shows neither lime nor phosphate, contain 

 them notwithstanding in large proportion in their 

 fixed principles — of which [or of the ashes] they 

 often compose half the mass.* 



Absorption of plants, in vegetation on cultivated 

 soils. 



32. Vegetation on uncultivated soils operates 

 under conditions altogether different, from those of 

 the cultivated, so that the results receive modifica- 

 tions which ii is important to examine. 



Nature produces, and continues to produce, all 

 the vegetable mass in spontaneous growth, with- 

 out any other condition than the alternation and 

 succession of (hi 1 species. In vegetation on culti- 

 vated land, by bringing together the same indi- 

 vidual plants which are to grow abundantly on a 

 soil and in a climate which, in most cases, are not 

 those which nature had designed, there are re- 

 quired, besides the general condition of alternation 

 of the species, frequent tillage, of the soil, and 

 means to repair its losses, that the culture may be 

 productive, and be continued. However, with these 

 new conditions, the force of absorption of plants 

 on the atmosphere still furnishes the greater part 

 of the vegetable principles in soils not limed — and 

 still more in limed soils. 



To form a precise idea, we will take it in the 

 land of the writer, its culture and its biennial ro- 

 tation. As the same qualities of soil are found 

 elsewhere, as no particular circumstance increases 

 or impairs its products, there would be found simi- 

 lar results, tor the same qualities of soil, with a 

 different culture. The inferences which we will 

 draw from ours, will apply then to all others. 



On our soil of the third class, [or worst quality] 

 fallow returns every two years, with a biennial 

 manuring of 120 quintals to the hectare. This 

 mass contains more than four-fifths of water, 

 which should not be counted as manure, and con- 

 sequently, the substance which serves for the repa- 

 ration of the soil is reduced to 24 quintals. We 

 reap, in rye, straw, and buckwheat, after the year 



* This fact is explained very differently by the Es- 

 say on Calcareous Manures (Ch. VII) where it is 

 used to sustain the doctrine of neutral soils. Ed. 



of fallow, a dry weight of 40 to 50 quintals on an 

 average. If it is supposed that all the manure is 

 consumed, or employed in forming vegetable sub- 

 stance, still the soil would have furnished IS to 20 

 quintals more than it received, and which excess 

 would be due to the power of absorption, whether 

 of the soil, or of the plants, on the atmosphere. 



On lands of middle quality, which yield a crop 

 every year, with a double manuring, that is to say, 

 of 48 quintals of dry manure, in two years there 

 is a product in wheat, maize, or potatoes, which 

 amounts to from 12 to 15,000 weight, 120 to 150 

 quintals, of which two-thirds, or 80 quintals at 

 least are derived from absorption. 



On soils of good quality, with a manuring of 

 one-third more than the last, which is equal to 64 

 quintals of the dry substance to the hectare, there 

 are obtained of dry products, ingrain, straw, roots, 

 or hay, double of the last, or nearly so, of which 

 three-fourths, or 180 quintals are due to the power 

 of absorption. 



Lastly — upon the most fertile soils, (sols (Pex- 

 ception,) where manures are useless, the product, 

 often double, or at least half as much more than 

 the last mentioned, will amount to 3G0 quintals to 

 the hectare in two years. This product would be, 

 as in spontaneous vegetation, entirely due to ab- 

 sorption. 



We would have then, to represent the products 

 of two years, in quintals, in the four classes of soil 

 under consideration, the progressive amounts of 

 42,130,240,360: or, by deducting from these pro- 

 ducts the weight of the manure, we would have, 

 to represent the power of absorption, the progres- 

 sion IS, 82, 176, 360 quintals. From this is de- 

 duced, as the first conclusion, that, supposing the 

 plants have consumed and annihilated all the sub- 

 stance of the manure given, (which is beyond the 

 truth,) plants receive a much greater part of their 

 substance from the atmosphere, than from the 

 soil; and that this power of drawing food from the 

 atmosphere increases with the goodness of quality 

 in soils. 



33. The proportion of fixed substances, or ashes, 

 in agricultural products, is 43 pounds to the 1000, 

 and consequently, in our four classes of land, the 

 quantity amounts to 180, 559, 1032, 1548 pounds. 

 But the soluble saline substances form at least half 

 of these ashes: they are then produced in the two 

 years of the rotation, in the quantities of 90, 279, 

 516, 774 pounds. But, according to Kirwan, barn 

 yard manure yields 2 per cent, of soluble salts: then 

 the manure given to these soils contained 48, 96, 

 lbs. 128 of saline substances, which being deducted 

 from the preceding quantities, leave the four 

 classes of soils stated, 42,183,3S8,774 lbs. of pro- 

 ducts in soluble salts, in two years of the rota- 

 tion, gained solely by the absorbing forces of the 

 soil and of plants.* 



*The proportions of ashes of different plants, and 

 of their saline matters, vary greatly — and the uniform 

 proportions assumed above, are far from correct, even 

 as averages of unequal proportions. This will suffi- 

 ciently appear from the following examples extracted 

 from Saussure's table of the products of various vege- 

 table substances. (See Davy's Agr. Chem. Lee. III.) 



