140 CHEMICAL MANURES. 



present it is Germany which manufactures the most chemical 

 manures to respond to the increasing demands of agriculture. 



Pkosjjhatic Mannres — Do they become Insoluble in the Soil ? — 

 The benefits of enriching the soil in phosphoric acid has sometimes 

 been questioned on the ground that phosphatic manures become 

 insoluble in the soil, and consequently inactive in a period of time 

 varying from one to three years. This objection has been refuted 

 by Dr. Wagner. If superphosphate or basic slag be buried and the 

 soil be left to itself without tilling it or sowing it, what happens ? 

 The result will be that the rain, filtering through the layer of soil, will 

 insensibly dissolve the phosphoric acid of the superphosphate and 

 the basic slag, and will transport it always a little further into the 

 subsoil, where it comes in contact with oxides of iron, alumina, and 

 lime. It will combine with these salts forming less and less soluble 

 compounds, to pass finally after fifty or a hundred years perhaps, 

 one does not know exactly, to almost the same state of insolubility 

 as the phosphoric acid contained in the minerals in the soil. 



" This transformation will require a very considerable time. It 

 is also certain that in a cultivated soil tilled, laboured, sov/n, and 

 manured, the process of being rendered insoluble is unceasingly op- 

 posed to the tendency to become insoluble ; the cultivated soil 

 opposes the contrary one, that of becoming soluble. The humic 

 acid, the carbonic acid, the nitrate of soda, the roots of plants, 

 fungi, bacteria, the circulation of air and moisture, are constant 

 agents of activity which do not allow the soluble phosphoric acid 

 to come to rest. As soon as precipitated phosphates are formed in 

 the soil with a portion of the phosphoric acid whether from super- 

 phosphates or basic slag, the agents in the soil just enumerated 

 exert their solvent action and bring back the phosphoric acid to the 

 soluble state, the lime, alumina, and oxide of iron reprecipitate it 

 again in part, the agents in the soil bring it back unceasingly to the 

 soluble state, and so on. The phosphoric acid, therefore, is not at 

 rest in the soil ; it passes from one state of combination into 

 another ; it unites to one element for a fleeting union and quits it 

 to unite to another element to form a union quite as ephemeral, 

 for the agents of combination and solution contained in the soil 

 are engaged in an incessant struggle to seize and carry away the 

 phosphoric acid for themselves ; sometimes it is the one, sometimes 

 the other, that remove it in a transitory fashion. But the phos- 

 phoric acid retains its instability. The more intensive the culture, 

 the more the soil is aerated, rich in humus, the more abundant the 

 manuring with nitrate, ammoniacal and potash salts, the deeper the 

 tilth, the heavier the crops, the less chance has the phosphoric acid 

 in excess entrusted to the soil of passing to the soluble state, at 

 least in large enough amount to occasion fears as to its action." 



In support of these arguments Wagner relates the results he 



