IN CEOPS AND MANURE. 



359 



SUMMARY. 



From all that precedes, it is obvious that rotations which include 

 trefoils, red clover, lucern, and sainfoin, are those that afford con- 

 siderably the largest proportion of organic matter ; a fact, indeed, 

 which if not legitimately established, has still been long acted on 

 in that system of cropping which embraces forage plants as an ele- 

 ment. Lucerns, too, when they have taken kindly, yield an extra- 

 ordinary quantity of forage, as every one may see by turning to the 

 produce of the piece under that crop which in the system of M.Crud 

 succeeds the quatrennial rotation. At the end of his rotation, M.Crud 

 always lays on manure in the ratio of 18 tons per acre, which lasts 

 for six years, and may be said to suffice for the succession of crops 

 in the appended table : 



Crops. 



Lucern dry, 



Wheat, 

 Straw .. 



Produce per acre. 



1st year 3080 lbs. 



2d year 9240 



3d year 114.58 



4th year 9240 



5th year 7333 



6th year 1448 



3645 



Dung employed 40233 



Contents in azote. 

 72 lbs. 

 215 

 269 

 213 

 172 



H 



980 

 205 



Total gain in azote 775 



Gain in azote per annum and per acre 130 



In glancing at these tables, it is obvious that the azote of the crop 

 always exceeds the azote of the manure. Generally speaking, I 

 admit that this excess of azote is derived from the atmosphere : but 

 I do not pretend to say in what precise manner the assimilation takes 

 place. I shall only quote the conclusion of a paper which I published 

 on the subject in the year 1837.* Azote may enter immediately into 

 the constitution of vegetables, provided their green parts have the 

 power of fixing it ; azote may also enter vegetables dissolved in the 

 water which bathes their roots, and which always contains it in a 

 certain proportion. Lastly, it is possible that the air may contain 

 an ii\finitely minute quantity of arnmoniacal vapor, as some natural 



* Annales de Chimie, t. Ixix. p. 3Cb. 



