6 VOELCKER on the Value of Artificial Manures. 



and vegetable matters -without doubt is the most valuable of all 

 fertilizing substances, and ought therefore to be present in every 

 good artificial general manure. 



Ammonia, nitric acid, and more or less decomposed nitro- 

 genized organic . matters, closely resemble each other in their 

 action. They all exercise a peculiar forcing effect, especially 

 when supplied to the plant at an early stage of its growth : at a 

 later period they appear much less effective. For this reason 

 nitrogenized manures, such as guano or soot, ought to be applied 

 to wheat, either in autumn or early in spring, immediately after 

 the young blade has made its appearance above ground. 



The effects of ammonia have been so well ascertained by 

 numerous experiments in which it has been applied, with the 

 exclusion of all other substances, that few practical men at the 

 present time will hesitate to ascribe the rapid forcing effects 

 of guano, soot, sulphate of ammonia, ammoniacal liquor of 

 gas-works, &c., to the ammonia which they contain. These 

 manures, as well as nitrate of soda and nitrates in general, in- 

 duce a luxuriant development of leaves, and may therefore be 

 called leaf-producing manures. Grass-land, wheat, and other 

 grain-crops are benefited by them in a striking manner ; but on 

 account of their special action they ought to be used with caution 

 in the case of corn-crops, and always more sparingly on light 

 than' on heavy land ; otherwise, splendid straw, but little and 

 an inferior sample of grain, will be obtained. 



As yet the question, whether nitrogen is more useful to plants 

 in the form of ammonia or nitric acid, has not been decided. 

 As the solution of this question is of considerable practical im- 

 portance, it is very desirable that the relative effects of nitrates 

 and ammoniacal salts should be ascertained by a series of well- 

 conducted comparative field experiments. 



Animal and vegetable organic substances containing nitrogen 

 in an unfermented state scarcely exhibit any fertilizing effects on 

 vegetation ; and it is only after their nitrogen has become 

 changed into ammonia or nitric acid that they become powerful 

 fertilizers. As the value of a manure depends in some degree 

 on the rapidity of its effects, the nitrogen in fresh animal or 

 vegetable substances is not quite so valuable as in the form of 

 ammonia or nitric acid. Nitrogenized manures likewise appear 

 to facilitate the assimilation of the mineral matters found in the 

 ashes of plants. As our fields are generally deficient in ammo- 

 nia or nitric acid, their presence in an artificial manure is of 

 great importance. Nitrogen, moreover, in either of the stated 

 combinations, is very expensive, and is therefore justly regarded 

 as the most valuable ingredient of artificial manures. 



2. Phosphoric Acid. Next in value follows phosphoric acid. 

 In artificial manures it generally exists in the form of bone- 



