ORGANIC ELEMENTS OF MANc^ES AND CROPS. 



363 



•UMMARY OF THE FOREGOING RESULTS. 



Nature of the 



residues buried 



in the soil. 



Potatoetops . 

 Beetroot leaves 

 Stubble. . . . 

 Roots dried in 

 the sun . . . 

 Stubble .... 



It therefore appears that the refuse or residue of the several crops 

 of a rotation represent, both in quantity and nature, somewhat 

 less than one half of the manure originally put into the ground ; I 

 say somewhat less, because it must be remembered that in the sum 

 of these residuary matters, the beetroot leaves and potato tops must 

 not be allowed to stand together, the one crop naturally excluding 

 the other, or at all events the two hoed or drilled crops not entering 

 in this proportion into the same rotation. 



The large quantity of organic matter restored to the soil by several 

 of the crops in the series, consequently explains how the rotation 

 may be closed without its being found indispensable to supply any 

 additional manure in its course. It seems indubitable that without 

 this addition of elementary matter, the fertility of the soil would 

 decline much more rapidly than it does ; the residue of each crop is 

 nothing more than a portion of the crop itself restored to the ground ; 

 it is as if we only carried off one portion, the larger portion of the 

 crop, and buried another portion green. 



In the five years' rotation, it may be observed that there are two 

 crops, the hoed crop and the forage crop, which yield substa^ices to 

 the ground that are both abundant in quantity and rich in azotized 

 matter, and it is unquestionable that these crops act favorably on the 

 cereals which succeed them. But data are wanting for the appre- 

 ciation of their specific utility in the general rotation. We see, for 

 instance, that despite the large proportion of residuary matter left by 

 the beet or mangel-wurzel, this plant lessens considerably the pro- 

 duce of the wheat crop that comes after it. The potato, though it 

 leaves much less refuse than the beet, seems nevertheless to act lesa 

 unfavorably than this vegetable. Clover leaves more residue than 

 the potato, and on this ground, alone, ought to favor the cereal that 

 follows it ; but it has a favorable influence out of all proportion with 

 its quantity, contrasting this with the residue of either of the hoed 

 crops ; a fact from which we learn that the visible appreciable influ- 

 ence of the residuary matters of preceding crops, upon the luxuriance 

 of succeeding crops, does not result solely from their mass, even 

 supposing earh to be possessed of equal qualities ; this other, this 



