CHEMICAL MANURES. 23 



substituting carbonate of potash for the nitrates that is to say, alka- 

 line and azotic products by a fertilizer without azote. 



I hasten to arguments drawn more directly from practice. 



Suppose you enrich peas, clover or lucerne with nitrate of soda. 

 The effect is radically nothing, if it is not decidedly injurious. Now, 

 how bring out in behalf , of these plants the good effects of a spon- 

 taneous nitrification in the soil ? 



We may make the argument more general. 



Try two parallel experiments : in one let the soil be enriched by a 

 fertilizer composed of phosphate of lime, of potash and lime without 

 azote ; in the other, add to these three agents some azotic matter. 

 Under these two conditions different effects will be shown according 

 to the nature of the plants. 



The clover, peas and legumes will thrive as well on the ground 

 which has not received the azote as on the other. With the grain, 

 the colza, the beet and tobacco the result will be different. Where 

 the azote is wanting the yield will be more than mediocre, while it 

 will be excellent from the soil supplied with it. 



What must we conclude from this contrast ? That plants form 

 two distinct groups : the first comprising those which draw azote 

 from the soil ; the second, those which take it in preference from the 

 air. 



Do you doubt it ? Here are other facts in support of this distinc- 

 tion. 



Every one knows that culture without fertilizers soon becomes un- 

 certain. The returns are never absolutely nothing, and the quantity 

 of azote corresponds in importance. 



According to Messrs. Lawes and Gilbert it reaches 



To 17.9 Ibs the acre per year for wheat. 

 " 24 " " " barley. 



" 39.1 " " " the meadow. 



" 47.1 " beans. 



We see by thi's table that the meadow and beans fix more azote 

 than barley and wheat. Shall we say that the azote of the beans 

 and the meadow comes from the soil ? We would thus raise a very 

 embarrassing difficulty. If you sow grain after beans, the return is 

 better and the quantity of azote fixed greater. On the other hand, 

 however, we maintain that the beans contain more azote than the 

 wheat. Is it not evident, then, if they had taken it from the earth 

 the yield from the wheat would show it ? 



Conclusions : 



Azote is absorbed under different forms : for legumes the elementary 

 azote, for wheat and colza the ammoniac, and for beets the nitrates, 

 are the most suitable forms. But we again repeat that all vegetables, 

 without distinction, show an excess of azote for which neither fer- 

 tilizers nor soil can account, and which can only be explained by 

 attributing it to the elementary azote of the air. 



Permit me to sum up the question in indisputable figures, to deter- 

 mine the importance of the quantity of azote plants draw from the air : 



