AGRICULTURAL CHEMISTRY. 



nution of fertility ID a soil is owing to the 

 loss of humus ; it is the mere consequence 

 of the exhaustion of the alkalies. 



Let us consider the condition of the coun- 

 try around Naples, which is famed for its 

 fruitful corn-land ; the farms and villages 

 are situated from eighteen to twenty-four 

 miles distant from one another, and between 

 them there are no- roads, and consequently 

 no transportation of manure. Now corn 

 has been cultivated on this land for thousands 

 of years, without any part of that which is 

 annually removed from the soil being artifi- 

 cially restored to it. How can any influ- 

 ence" be ascribed to humus under such cir- 

 cumstances, when it is not even known 

 whether humus was ever contained in the 

 soil? 



The method of culture in that district 

 completely explains the permanent fertility. 

 It appears very bad in the eyes of our agri- 

 culturists, but there it is the best plan which 

 could be adopted. A field is cultivated once 

 every three years, and is in the intervals 

 allowed to serve as a sparing pasture for 

 cattle. The soil experiences no change in 

 the two years during which it there lies fal- 

 low, farther than that it is exposed to the 

 influence of the weather, by which a fresh 

 portion of the alkalies contained in it are 

 again set free or rendered soluble. The ani- 

 mals fed on these fields yield nothing to 

 these soils which they did not formerly pos- 

 sess. The weeds upon which they live 

 spring from the soil, and that which they 

 return to it as excrement must always be less 

 than that which they extract. The fields, 

 therefore, can have gained nothing from the 

 mere feeding of cattle upon them ; on the 

 contrary, the soil must have lost some of its 

 constituents. 



Experience has shown in agriculture 

 that wheat should not be cultivated after 

 wheat on the same soil, for it belongs with 

 tobacco to the plants which exhaust a soil. 

 But if the humus of a soil gives it the power 

 of producing corn, how happens it that 

 wheat does not thrive in many parts of 

 Brazil, where the soils are particularly rich 

 m this substance, or in our own climate, in 

 soils formed of mouldered wood ; that its 

 stalk under these circumstances attains no 

 strength, and droops prematurely ? The 

 cause is this, that the strength of the stalk is 

 due to silicate of potash, and that the corn 

 requires phosphate of magnesia, neither of 

 which substances a soil of humus can afford, 

 since it does not contain them; the plant 

 may, indeed, under such circumstances, be- 

 come an herb, but will not bear fruit. 



Again, how does it happen that wheat 

 does not flourish on a sandy soil, and that a 

 calcareous soil is also unsuitable for its 

 growth, unless it be mixed with a consider- 

 able quantity of clay ?* It is because these 



* In consequence of these remarks in the former 

 edition of this work, Professor Wohler of Gottin- 

 gen has made several accurate analyses of diffe- 



soils do not contain alkalies in sufficient 

 quantity, the growth of wheat being arrested 

 by this circumstance, even should all othei 

 substances be presented in abundance. 



It is not mere accident that only trees ot 

 the fir tribe grow on the sandstone and lime- 

 stone of the Carpathian mountains and the 

 Jura, whilst we find on soils of gneiss, mica- 

 slate, and granite in Bavaria, of clinkstone 

 on the Rhone, of basalt in Vogelsberge, and 

 of clay-slate on the Rhine and Eifel, the 

 finest forests of other trees, which cannot be 

 produced on the sandy or calcareous soils 

 upon which pines thrive. It is explained 

 by the fact that trees, the leaves of which 

 are renewed annually, require for their 

 leaves six to ten times more alkalies than the 

 iir-tree or pine, and hence when they are 

 placed in soils in which alkalies are con- 

 tained in very small quantity, do not attain 

 maturity.* When we see such trees grow- 

 ing on a sandy or calcareous soil the red- 

 beech, the service-tree, and the wild-cherry 

 for example, thriving luxuriantly on lime 

 stone, we may be assured that alkalies are 

 present in the soil, for they are necessary to 

 their existence. Can we, then, regard it a? 

 remarkable that such trees should thrive in 

 America, on those spots on which forests 

 of pines which have grown and collected 

 alkalies for centuries, have been burnt, and 

 to which the alkalies are thus at once re- 

 stored ; or that the Spartium scoparium, 

 Erysimum latifolium, Blitum capital um, *Se- 

 necio viscosus, plants remarkable for the 

 quantity of alkalies contained in thf : ashes, 

 should grow with the greatest luxuriance on 

 the localities of conflagrations ?f 



Wheat will not grow on a soil which has 

 produced wormwood, and vice versa, worm- 

 wood does not thrive where wheat has 

 grown, because they are mutually preju- 

 dicial by appropriating the alkalies of the 

 soil. 



One hundred parts of the stalks of wheat 

 yield 15-5 parts of ashes (H. Davy;) the 

 same quantity of the dry stalks of barley, 



rent kinds of limestone belonging to the secondary 

 and tertiary formations. He obtained the remark- 

 able result, that all those limestones, by the dis- 

 integration of which soils adapted for the culture 

 of wheat are formed, invariably contain a certain 

 quantity of potash. The same observation has 

 also recently been made by M. Kuhlman of Lille. 

 The latter observed that the efflorescence on the 

 mortar of walls consists of the carbonates of soda 

 and potash. 



* One thousand parts of the dry leaves of oaks 

 yielded 55 parts of ashes, of which 24 parts con- 

 sisted of alkalies soluble in water ; the same 

 quantity of pine-leaves gave only 29 parts of ashes, 

 which contain 4.6 parts of soluble salts. (De 

 Saussure.) 



t After the great fire in London, large quanti- 

 ties of the Erysimum latifolium where observed 

 growing on the spots where a fire had taken place. 

 On a similar occasion the Blitum capitalum was 

 seen at Copenhagen, the Senecio viscosus in Nas- 

 sau, and the Spartium scoparium in Languedoc. 

 After the burnings of forests of pines in North 

 America, poplars grew on the same soil. 



