CHEMICAL MANURES. 67 



turns are impossible from manure alone, because the sum of its dis- 

 posable assimilable agents is not great enough. And now, if I remind 

 you that azotic matter is the dominant of wheat, colza and the beet; 

 potash of the legumes ; phosphate of lime of the turnip ; that the 

 mineral without the azote gives the largest return of lucerne; that the 

 minerals with the addition of a little azote are best for flax and Irish 

 potatoes, you will not only perceive the rules which guided me in the 

 preceding demonstrations, but you will be able by their aid to form ro- 

 tations most appropriate to the circumstances in which you are placed. 

 This is not all. That the solution of the problem of agriculture 

 may be complete, we must not only "know the agents which are the 

 source of fertility, but must be also certain that their use is not a 

 cause of decay .-of soil, and that they do not take more from it than 

 they return to it. 



So, to give the examination of this subject a character of severity, 

 precision, and at the same time a generality which makes my conclu- 

 sions without appeal and applicable in all possible cases, I embody 

 them in these terms : Can we indefinitely cultivate the same land with 

 chemical fertilizers, and with the same success f My reply is absolute : 

 Yes, that is possible, but always under two conditions: 



1st. Give the land, through fertilizers, more phosphate of lime, 

 more potash and more lime than the harvests have taken fijom it. 

 2d. Give it about 50 per cent, of azote to the harvest. 

 I say about, because there are some plants requiring less, and others 

 can do without it entirely. 



Here the first question presents itself : Why more minerals and less 

 or no azote ? Why ? But you have already answered. Because a 

 part of the azote of plants comes from the air, and there are even some 

 which draw it entirely from that source. The quantity of azote given 

 the soil varies from 6 to 50 per cent., according to the plant. If we 

 have to do with the legumes, it is 6 ; if we pass to wheat, it is 50 per cent. 

 We must return an excess of phosphate of lime, potash and lime 

 over what the land loses, because plants draw them exclusively from the 

 soil, and we must not only compensate the soil for the loss determined 

 by each harvest, but repair that resulting from the action of the rain. 

 Let us examine if the formula of fertilizers I have prescribed will 

 fill the two conditions I have just pointed out. 



I told you in my last lecture that wheat may be cultivated upon the 

 same land indefinitely, provided it is furnished in four years with the 

 following quantities of fertilizers, thus divided : 



A Succession of Four Years in Wheat. 



First Year Wheat. 

 Complete fertilizer No. 1, 1066 Ibs. 



Composition: Quantity. U Price. 



Acid phosphate of lime 355 Ibs. $5.40 



Nitrate of potash 177 " 10.47 



Sulphate of ammonia 222 " '9.50 



Sulphate of lime 311 " .64 



Cost... . $26.01 



