THEORETICAL VALUE OF VEGETABLE MANURES. 441 



^n&y severally contain, { Annates de Ckemieet de Phys.^ 3d series, III., 

 D. 76. ) And taking farm-yard manure — consisting of the mixed drop- 

 ings and litter of cattle — as a standard, they arrange vegetable sub- 

 dances, as manures, in the following order of value : — 



Equal effects are produced by 



Farm-yard manure '. 1000 lbs. 



Potatoe and turnip (?) tops 750 " 



Carrot tops 470 « 



Natural grass 760 " 



Clover roots 250 " 



Fresh sea-weed 450 to 750 " 



Sea-weed dried in the air 300 " 



Pea straw 220 " 



Wheat straw 750 to 1700 « 



Oat straw • . . 1400 " 



Barley straw 1750 " 



Rye straw 1000 to 2400 <' 



Buck-wheat straw 850 " 



Wheatchaff 470 " 



Fir saw-duyt 1700 to 2500 « 



Oak do 750 « 



Soot, from coal 300 " 



Lint and rape-dust 80 " 



The numbers in this table agree with the results of experiment in 

 so far as they indicate that green substances generally, when ploughed 

 in as manures, should enrich the soil more tnan an equal weight of 

 farm-yard manure — that the roots of clover should be more enriching 

 still — and that sea-weed is likewise a very valuable manure. They 

 agree also with practical observation in placing pea, and probably 

 bean straw, far above the straws of wheat, oats, &c., in fertilizing 

 power, and in representing soot and rape-dust as more powerful than 

 any of the other substances in the table. ' So far, therefore, a certain 

 general reliance may be placed upon the fertilizing value of a sub- 

 stance as represented by the proportion of nitrogen it contains. 



But if we bear in mind that plants, as we have frequently had occa- 

 sion to mention, require inorganic as well as organic /oo(Z, it is quite 

 clear that the mere presence of nitrogen in a substance is not sufficient 

 to render it highly nutritive to growing plants. Otherwise the salts 

 of ammonia would be the richest manures of all, and would best nourish 

 and bring to perfection every crop and in all circumstances — which ex- 

 perience has proved to be by no means the case. Hence 



2°. The value of vegetable substances as manures must depend in 

 some degree wpon the quantity and kind of inorganic matter they 

 contain. In reference to the quantity of inorganic matter which they 

 respectively impart to the soil, their relative values are represented 

 by the following numbers : — 



