AgricuUwal Chemistry. SOT 



In 1843 I formulated in the following manner these natural 

 laws of the manuring of soils. (' Agr. Chem.,' see Appendix, 

 where they are printed in full connexion, pp. 211 to 214.) 



" We cannot au2,-mcnt the fertility of our fields, or their power of produc- 

 tion, by supplying them with manure rich in nitrogen, or with ammoniacal 

 salts alone. The crops of a field diminish or increase in exact proportion to 

 the diminution or increase of the mineral substances conveyed to it in the 

 manure."' — p. 211.* 



For the illustration of this sentence, and that the meaning 

 conveyed by it might not be doubtful, I added the following 

 sentences, in reading which, it must be borne in mind, that I had 

 m view three kinds of manure, ammoniacal salts alone, am- 

 moniacal salts loith mineral constituents, and mineral constituents 

 ulone. 



In these sentences I said — 



1. " If the mineral constituents are wanting in the maniire, and if we give 

 ammonia alone, no nitrogen is assimilated, and no crop is obtained." — p. 211. 



2. " The ammonia in animal excreta only exerts so favourable an influence, 

 because it is accompanied by mineral constituents." — p. 212. 



3. " It follows from this, that ammonia is assimilated when it is accom- 

 panied by these mineral constituents." 



4. " When ammonia is wanting in the manure — that is, when it con- 

 tains only the mineral constituents — the nitrogen, is obtained from the 

 atmosphere." 



In order to remove any doubt as to the meaning of this pro- 

 position, the following one is subjoined in my book : — 



" Ammonia accelerates and favours the growth of plants on all kinds of 

 soil, in which exist the conditions for its assimilation ; but it is quite without 

 action where these conditions do not exist." 



Fearing that these propositions might nevertheless be mis- 

 understood, and that the false doctrine might be ascribed to me, 

 that the produce of the soil was dependant solely on the supply 

 of mineral constituents, the following sentence was added in the 

 English edition (p. 213) : — 



" In order to obviate any misunderstanding, we must again draw attention 

 to the fact that this explanation is not in any way contradicted by the effect 

 produced by the application of artificial ammonia or its salts. Ammonia 

 was, and is still, considered as the source of all the nitrogen of plants ; its 

 supply is never injurious ; on the contrary, it is always useful, and, for certain 

 purposes, indispensable. lUit, at the same time, it is of great imj^ortancc for 

 agriculture to know, that the supply of ammonia is unnecessary for most of 

 our cultivated plants, and that it may be even superfluous, if only the soil 

 contain a sufEcieut supjily of the mineral food of plants, when the ammonia 



* In the German edition, of which the English is a translation, this sentence 

 stands thus : " instead of " the crops of a field " it is " the power of production of 

 a field " (in German, " seine Produktionsvermogen). — Author. 



This error is liere of little moment, because in the preceding sentence, as above 

 quoted, the terms "fertility" and "power of production," both accurately repre- 

 senting the German, are used. — Tkanslator. 



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