24 CHEMICAL MANURES. 



Excess of azote in crop 

 over amount contained 

 in fertilizer. 



Wheat 53.33 Ibs. 



Peas 62.22 " 



Colza 115.55 



Beets 115.55 " 



Lucerne 266.66 " 



In the preceding examples the fertilizer contains from 44 to 53.33 

 pounds of azote per acre. As to lucerne, I have taken the excess 

 from a purely mineral fertilizer, and from a yield fixed at 7111 

 pounds. 



You see, then, by these examples, that though all vegetables show 

 an excess of azote, this excess is far from being of the same import- 

 ance to each. 



There is still a distinction to be made with regard to the conditions 

 under which it is produced. 



There are plants which contain a great deal of azote, though we do 

 not furnish them by manures : peas, beans, clover and lucerne come 

 under this head. There are others which show a considerable excess 

 of azote, but which must have it given them by fertilizers containing 

 azote ; such are in particular beets and colza. Lastly, there is a third 

 list of plants which require a great deal of azote in the soil, and 

 whose crops yield relatively but a small excess, such as wheat. 



These clifFerences have a practical signification, which it is of the 

 last importance we should not misunderstand. Who cannot see im- 

 mediately, and from these simple general facts, that there is an advan- 

 tage to be gained under the double relation of returns and improve- 

 ment of soil, by alternating wheat with beets, and above all with 

 1 c mimes ; that is to say, the plants which draw their azote from the 

 soil with those which draw it from the air ? 



Experience confirms, this anticipation on all points. 



You all know that wheat succeeding clover yields more than when 

 preceding it. Who does not know how favorable it is to the culture 

 of wheat to turn under the leaves of the beet ? There is still an im- 

 portant remark to be made concerning those plants (like the beet) 

 which demand large quantities of azote in the soil ; that is, that the 

 excess of azote in the crop is somewhat proportional to the quantity 

 the soil has received. It results, then, that those plants are not most 

 beneficial to the soil which require the least azote in their fertilizers, 

 but those which exhibit the greatest excess of azote at the expense 

 of the atmosphere. This relation, this correspondence between the 

 richness of the fertilizer and the benefit to the plant receiving it, of 

 which science now gives us- the explanation, has long been confirmed 

 by practice, as the words of Matthew de Dombasle testify. It is a fact 

 generally observed, says he, that the functions by which plants appro- 

 priate the nutritive elements contained in the soil and air are corre- 

 sponding functions, so that an increase in the quantity of the principles 

 which they draw from the soil can alone fit them to appropriate a 

 greater quantity of atmospheric food. For this reason plants are 



