THE SOIL. 67 



The precise amount necessary cannot be fixed at 

 any particular proportion ; probably five parts in a 

 hundred is better than a smaller amount. 



The soil obtains its atmospheric matter in two 

 ways. First, by the decay of roots and dead plants, 

 also of leaves, which have been brought to it by 

 wind, etc. Second, by the application of animal or 

 vegetable manures. 



When a crop of clover is raised, it obtains its car- 

 bon from the atmosphere ; and, if it be ploAved 

 under, and allowed to decay, a portion of this carbon 

 is deposited in the soil. Carbon constitutes nearly 

 the whole of the dry weight of the clover, aside from 

 the constituents of water ; and when we calculate 

 the immense quantity of hay and roots grown on 

 an acre of soil in a single season, we shall find that 

 the amount of carbon thus deposited is immense. 

 If the clover be removed, and the roots only left to 

 decay, the amount of carbon deposited would still be 

 very great. The same is true in all cases where the 

 crop is removed, and the roots remain to add to the 

 organic or vegetable part of the soil. While under- 

 going decomposition, a portion of this matter escapes 

 in tlie form of gas, and the remainder chiefly assumes 

 the form of carbon (or charcoal), in which form it 

 will always remain, without loss, unless driven out by 

 fire. If a bushel of charcoal be mixed with the soil 

 now, it M'ill be the same bushel of charcoal, neither 

 more nor less, a thousand years hence, unless some 

 influence is brought to bear on it aside from the 

 growth of plants. It is true that, i i the case of the 



