146 PROPORTIO> OF CARBON DRAWN FROM THE AIR. 



If we were to examine the soil of a field on which we are about to 

 raise a crop of corn — and should find it to contain a certain per-centage, 

 say 10 per cent, of vegetable matter (or 5 per cent, of carbon) ; — and 

 after the crop is raised and reaped should, on a second examination, 

 find it to contain exactly the same quantity of carbon as before, we 

 could not resist the conviction, that, with the excejjtion of what was 

 originally in the seed, the plant during its growth had drawn from the 

 air all the carbon it contained. The soil having lost none, the air must 

 have yielded the whole supply. 



Or if after examining the soil of our field we mLx whh it a supply of 

 farm-yard manure, containing a known weight, say one ton of carbon, 

 and when the crop is reaped find as before that the per-centage of vege- 

 table matter in the soil has suffered no diminution,* we are justified in 

 concluding that the crop cannot, at the utmost, have derived from the 

 soil any greater weight of its carbon than the ton contained in the ma- 

 nure which had been added to it. 



Such was the principle on which Boussingault's experiments were 

 conducted. He determined the per-centage of carbon in the soil before 

 the experiment was begun — the weight added in the form of manure — 

 the quantity contained in the series of crops raised during an entire rota- 

 tion or course of cropping, until in the mode of culture adopted it was 

 usual to add manure again — and lastly, the ])roporiion of carbon re- 

 maining in the soil. By this method he obtained the following results 

 in pounds per English acre, in three different courses of cropping, and 

 on the same land : — 



Carbon Carbon Difference, or 



in the in Carbon derived Remarks. 



majiure. the crops. from the air. 



f The first was a 5 years' 

 course — of potatoes or 

 red beet with manure, 

 wheat, clover, wheat, 

 oats; the second and 

 most productive rota- 

 tion was abandoned on 

 account of the climate ; 

 the third was a 3 yeans' 

 course. 



The result of the first course indicates that — the land remaining in 

 equal condition at the end of the four years as it was at the beginijing — 

 the crops collected during these years contained three times the quantity 

 of carbon present in the manure, and therefore the plants, during their 

 growth, must on the whole have derived tivo-thirds of their carbon from 

 the air. 



It will be shown in a subsequent section that even when the soil is 

 lying naked the animal and vegetable matter it contains is continually 

 undergoing diminution, owing to decomposition and the escape of vola- 

 tile substances into the air. It is fair, therefore, to assume that a con- 



-* I need scarcely remark that, in the hands of a good farmer, who keeps his land in good 

 heart — the quantity of organic matter in the soil at the end of his course of cropping should 

 be as great, atlea.st, as it was at the beginning of his rotation, before the addition of the 

 manure. 



First Course 2513 7544 5031 



Second do. — — 6839 { 



Third do. — — 3921 



