442 INFLUENCE OF THE CARBCNACEOUS MATTER. 



One ton contains of inorganic 

 mafier about 



Potato tops, green 26 lbs. 



Turnip tops, do 48 " 



Carrot tops, do 45 " 



Rye-grass, do 30 " 



Vetch, -do 38 " 



Green sea-weed, do 22 " 



Hay 90 to 180 " 



Pea straw 100 " 



Bean straw 60 to 80 « 



Wheat straw 70 to 360 " 



Oatstraw 100 to 180 " 



Barley straw 100 to 120 " 



Rye straw 50 to 70 « 



Fir saw-dust 6 " 



Oak saw-dust 5 ' 



• Soot ^ 500 



Rape-dust 120 



This table places the several vegetable substances in an order of 

 efficacy considerably different from the former, in which they are 

 arranged according to the quantity of nitrogen they respectively con- 

 tain. We know that wood-ashes (p. 353), kelp, and the ashes of straw 

 (p. 356), do promote the fertility of the land, and therefore the abso- 

 lute as well as the relative efficacy of the above vegetable substances 

 must depend in some degree upon the quantity of inorganic matter 

 they contain. But we should be wrong were we to ascribe the total 

 effect of any of them to the inorganic matter alone. 



3°. Even the carbonaceous matter of plants contributes its aid in 

 increasing the produce of the soil, by supplying, either directly or in- 

 directly, a portion of the necessary food of plants. This has already 

 been shown in various parts of the preceding lectures. 



It is the property of substances which contain a larger proportion 

 of nitrogen, to undergo rapid decay in the presence of air and moisture, 

 and thus to produce a more immediate and sensible action upon grow- 

 ing plants. But the carbon changes more slowly, and the inorganic 

 matter also separates slowly from decaying vegetables in the soil — 

 and hence the apparent effects of these constituents are less striking. 

 Thtis the immediate and visible effect of different vegetable substances, 

 in the same state, is measured by the relative quantities of nitrogen 

 they contain — their 'permanent effects by the relative quantities of in- 

 organic and of carbonaceous matters. In the case of rape-dust, for ex- 

 ample, the immediate effect is determined chiefly by its nitrogen — the 

 permanent effects, by the ash it leaves when burned, or when caused 

 to undergo complete decay in the air. 



