Man inhales air, composed principally of nitrogen and 

 oxygen, and exhales nitrogen and carbonic gas, the latter of 

 which contains carbon. Plants absorb the carbonic acid gas 

 from the air, retain the carbon and exhale oxygen, but 

 they have no power of appropriating through the leaves 

 any part of the abundant supply of nitrogen which surrounds 

 them in the atmosphere. The nitrogen which they require 

 must be obtained, except in the clover family, from decayed 

 or decaying organic matter in the soil — which contains nitro- 

 gen, as we have seen, — the accumulation of decayed roots and 

 leaves in virgin soils for ages and which is often designated as 

 humus. When the available nitrogen from these virgin or 

 natural sources is exhausted, it must be obtained from artificial 

 sources or by plowing in green crops. 



The inorganic matter, or ash group, we find to consist of a 

 number of minerals, all of which are present in available forms in 

 most soils, excepting phosphorus (phosphate of lime), potassium 

 (potash), and calcium (lime). Experience shows that if we supply 

 the phosphorus in the shape of phosphate of Hme, the character- 

 istic and predominating element of bone, and potash in the form 

 of ashes or in the form of potash salts fovmd in nature, and some- 

 times a little lime to sweeten the soil and occasionally some sand 

 in the case of peat soils, we are supplying the important constitu- 

 ents, or the "Httle balance," that is necessary for successful crop 

 production. Therefore, to sum up the problem, through analyses 

 of crops, analyses of soils, and experiments, also through prac- 

 tical farm operations conducted for more than half a century, 

 it has been observed that the three essential things to be 

 supplied in all commercial manures are nitrogen, phosphoric acid 

 and potash. 



Carbon 



and 



Oxygen 



The 



Little 

 Balance 



